In this work the experimental results on the
thermoelectric properties of the bulk p-type
oxyselenides Bi_1-xPr_xCuSeO (x = 0, 0.04, 0.08) and Bi_0.96La_0.04CuSeO
were presented. Specimens were fabricated by a two-step solid-state reaction
followed by spark plasma sintering. The temperature dependencies of the
thermopower, the electrical resistivity, and the thermal conductivity were
measured from room temperature to 800 K. It was revealed, that Bi to
rare-earth element substitution leads to an enhancement of the charge carriers
concentration, while the charge carriers mobility was not affected by the
substitution level. According to the obtained results of energy dispersive and
X-ray diffraction analyses, it was suggested that the main mechanism of changes
in the electrophysical properties of the BiCuSeO compounds under study was the
formation of bismuth vacancies when bismuth was replaced by rare-earth
elements. Considering that compounds based on BiCuSeO are p-type semiconductors, the formation of such vacancies should lead
to an increase in the concentration of holes,
thus the concentration of the main charge carriers also should be
enhanced. Moreover, a change in the slope of the electrical resistivity
temperature dependencies curves in the region of 350 K was observed, which
apparently corresponds to the α-CuSe → β-CuSe phase transition.
Furthermore, the presence of the CuSe
phase can be an indirect sign of the presence of bismuth deficiencies in the
compound, as was shown in previous works. It was also established that for all
the samples at temperatures above 160 K, charge carrier scattering on acoustic
phonons predominated; the contribution of the magnetic moment of rare-earth
elements to the transport properties was not observed. The obtained results
allow us to conclude that the replacement of bismuth ions with rare-earth
elements can be used to increase the charge carriers concentration due to the
formation of bismuth vacancies while the charge carriers mobility values remain
at the same level, which is impossible for alkali and alkaline-earth metals as
doping element.

Thermoelectric properties of
Sb₂Te₃ nanocomposites

V.A.Kulbachinskii¹, V.G. Kytin¹, D.A. Zinoviev, N.V. Maslov¹, P. Singha², S. Das², A. Banerjee²

¹
M.V. Lomonosov Moscow State University, 119991 GSP-1, Moscow, Russia

²Department of Physics, University of
Calcutta, 92 A P C Road, Kolkata 700009, India

kulb@mig.phys.msu.ru

The thermoelectric figure of
merit can be improved by nanostructuring of material [1] and immersing inside
scattering centers for phonons to reduce thermal conductivity without influence
on electron transport [2]. We synthesized by solid state reaction and
investigated Sb₂Te₃ nanocomposites with graphite. The
structure of samples was investigated by X-ray diffraction. We have performed
Rietveld refinement using atomic positions of all the synthesized Sb₂Te₃+x%(graphite)
(x=0.0, 0.5, 1.0) samples. The estimated grain size is around 15 nm. The XRD
patterns reveal that, samples are single phase in nature without presence of
impurity phases in the detectable limit. All the XRD peaks can be indexed with
rhombohedral crystal structure of Sb₂Te₃ phase having <![if !vml]><![endif]> space group
symmetry. No additional peaks due to graphite are observed in Sb₂Te₃+x%graphite
nanocomposite samples. The reason is that the amount of graphite is quite small
and beyond the detection limit of XRD. Further, XRD results confirm the solid
state insolubility of graphite phases in Sb₂Te₃ as no
shift was observed in the peaks corresponding to Sb₂Te₃
in the composite samples. Raman scattering showed a presence of two phases Sb₂Te₃
and graphite. Adding of graphite in nanocomposite increases resistivity in the
whole temperature range, decreases thermal conductivity and increases thermopower.

[1] Das D., et. al., EPL, 113, 47004-p1–p6
(2016).

[2] V.A. Kulbachinskii,
et.al., J. Sol. St. Chem. 193, 64–70
(2012).

New way of application for
thermoelectric energy converters

Z.M. Dashevsky¹, P.P. Konstantinov², S.Ya.Skipidarov³

¹ Ferrotec Nord Corporation, 109383 Moscow, Russia

² Physicotechnical Institute Russian Academy of
Sciences, 194021 St. Petersburg, Russia

³RusTec
LLC, 109383 Moscow, Russia

dashevsky.45@mail.ru

In south countries, solar collectors are widely used as an additional
water heating system. However, the disadvantage of such systems is that with
increasing water temperature, a significant part of solar energy can’t be used
and dissipated into the environment. It is proposed to use thermal waste heat
at high temperature, which is fed to a thermoelectric generator (TEG),
operating at a temperature difference between hot water in the solar collector
and cold water,
supplied to the radiator on the other side of the TEG. This is a new
application of thermoelectric converters, in which it can act not only as a
source of electrical energy, but also as a source of low-potential heat coming
out from the radiator. In this case, the total conversion in such devices can
reach 90 %. In the work with the goal of optimal efficiency of TEG conversion
it is detected the effect of the thermoelectric efficiency Z increasing for thermoelectric materials based on solid solutions
Bi₂Te₃ – Sb₂Te₃ of p-type conductivity, which are at
operating range temperature 50 – 300 ^oC.

Thermoelectric generators
for small temperature ranges

L.D. Ivanova

Institution of Russian Academy of Sciences A.A. Baikov Institute of
Metallurgy and Materials Science RAS

ivanova@imet.ac.ru

The analysis of the latest achievements of science in the field of creation of thermoelectric generators (TEG) for the direct conversion of thermal energy of the human body into electrical energy has been carried out.

Literature data on hard and flexible types of thermoelectric generators, their designs and methods of production are considered.

To obtain such TEG, electrochemical deposition, photolithography, etching, melt spinning, spark plasma sintering, sputtering, and screen coating are used.

Data on the magnitude of the efficiency (power and voltage) achieved on various TEG with temperature differences of 6 to 70 K are given.

Materials on the basis of
bismuth and antimony tellurides received by rapid melt solidation methods

L.D. Ivanova, Yu.V.Granatkina, A.G. Malchev, I.Yu.Nikhezina, M.V. Emel’yanov

IMET RAS

granat@imet.ac.ru

The materials of p-type conductivity Bi_0.5Sb_1.5Te₃
solid solution obtained by vacuum hot-pressing and extrusion powders
prepared by rapid melt quenching methods: melt spinning and melt
crystallization in liquid are investigated.

The morphology of
powder and sample cleavage surface and their microstructure are analyzed by
optical, scanning electron microscopy and scanning tunneling microscopy.

The mechanical properties of
the samples are investigated by compression tests at room temperatures.

The Seebeck coefficient, electrical
conductivity, and thermal conductivity of the materials were measured in the
temperature range 100–600 K.

The samples
extruded from granules obtained by melt crystallization in a water and crushed in a ball mill
have the highest strength s_B = 100 – 140 MPa at 300 K and the maximum thermoelectric
efficiency amounts to (ZT)_max= 1.2 – 1.3.

Materials on the basis
of bismuth chalcogenides n-type
conductivity received by melt solidification in
liquid

L.D. Ivanova, Yu.V. Granatkina, A.G. Malchev, I.Yu. Nikhezina, M.V. Emel’yanov, D.S. Nikulin

LLC “TERMOINTECH”

msk@termointech.ru

The microstructure, mechanical and thermoelectric properties of n-type
conductivity Bi₂Te₃−Bi₂Se₃
solid solution samples with 6, 8 and 10 mole % Bi₂Se₃
doped with antimony iodide, cadmium chloride and hexabromobenzene are
investigated. The samples were obtained by hot pressing and extrusion of granules
prepared by melt crystallization in a liquid and ground in a mortar, in a
cutting mill and in a ball mill.

The measurements were carried out at room temperature and in the range 100−600 K.

Conditions for obtaining of materials with the ultimate strength s_B~ 250 MPa under compressive
deformation at 300 K (composition with 10 mole % Bi₂Se₃doped with hexabromobenzene) are found.

Maximum
thermoelectric efficiency of investigated materials (ZТ)_max~0.9 in temperature
range 320−430 K.

Thermoelectric properties of n-Mg₂(SiGe)_0.8Sn_0.2solid
solution.

G.N. Isachenko^1,2, A.Yu.Samunin¹, P.P. Konstantinov¹, A.A. Kasyanov², A. Masalimov²

¹Ioffe Institute, St. Petersburg,
Russia

²ITMO University, St. Petersburg,
Russia

g.isachenko@mail.ioffe.ru

A low thermal conductivity and a complex band
structure, which is optimal at a ratio of a solid solution of 40% Mg₂Si
to 60% Mg₂Sn provide high values of the figure of merit (ZT = 1.4)
in Mg₂Si-Mg₂Sn solid solutions. However, the presence of
magnesium stannide in large quantity impairs the mechanical properties and
chemical stability of the material; restrict its use at high temperatures. On
another hand, magnesium silicide has higher stability, but loses in figure of
merit. The figure of merit is much lower in Mg₂Si-rich solid
solutions (ZT = 1). The possibility of increasing ZT in a solid solution Mg₂Si_0.8Sn_0.2
with additional inclusion of a small amount of Mg₂Ge was
investigated in this paper. Samples of the solid solution Mg₂(Si_1‑XGe_X)_0.8Sn_0.2
(X <0.03) were prepared by hot pressing. The temperature dependences in
range of 300-800 K of the Seebeck coefficient, electrical conductivity and
thermal conductivity were measured. An increase in the thermoelectric figure of
merit to ZT = 1.1 is shown at T = 800K in a solid solution Mg₂Si_0.78Ge_0.02Sn_0.2.

Investigation of the
thermoelectric properties Mg₂Si_0.8Sn_0.2 solid
solutions doped with Ca and Sb.

G.N. Isachenko^1,2, A.Yu. Samunin¹, P.P. Konstantinov¹, S.A. Tcupka², K.L. Samusevich^1,2

¹ Ioffe Physical-Technical Institute, Saint Petersburg, Russia,

² ITMO
University, Saint Petersburg, Russia,

g.isachenko@mail.ioffe.ru

The thermoelectric properties of solid solutions Mg₂Si-Mg₂Sn
can be improved by complex doping. Some researches of calcium inclusions in the
solid lattice of magnesium silicide for thermoelectric properties have shown a
decrease in the thermal conductivity of the crystal lattice and an increase in
the ratio of electrical conductivity to thermal conductivity. Therefore, the
Calcium influence at the thermoelectric properties of the solid solution Mg₂Si_0.2Sn_0.8
was investigated. Mg_2-xCa_xSi_0.2Sn_0.8
(X = 0.05, 0.1) samples from nanosized powder were prepared by hot pressing.
The samples were additionally doped with antimony for obtain n-type
conductivity with free carrier concentration of 10^-20cm³.
Their electrical conductivity, thermal conductivity and Seebeck coefficients
were measured. The obtained results were compared with the properties of these
solid solutions without calcium.

Dimensionless mathematical
model of a thermoelectric cooler: dTmax mode

A.A.
Melnikov^1,¶), O.M. Tarasov², A.V. Chekov², M.A.Bashkin³

¹ All-Russian Institute of Aviation
materials 105005 Moscow, Russia

² NUST «MISiS» 119049 Moscow, Russia

³ AO «NPO «Orion» 111538 Moscow,
Russia

q.melnikov@gmail.com

Thermal
resistances on cold an hot sides significantly affect output characteristics of
a thermoelectric device. A dimensionless mathematical model of a thermoelectric
cooler, calculating such parameters as optimal thermal resistance ratio and
optimal current, and taking into account thermal resistances is proposed.
Maximum temperature difference dT_maxmode is described. It is shown that optimal parameters of a cooler for dT_max and Q_max modes are different. For
dT_max mode, thermal
resistance on the hot side is crucial and optimal current is 0,4 – 0,7 relative
to maximum current for most cases when a material with ZT = 1 is used. It is shown that a decrease in thermal
conductivity of a thermoelectric material reduces the influence of thermal
resistance on the hot side and additionally increases dT_max besides an increase in ZT. An increase in length
of thermoelectric pellets has the same positive effect.

Structure and properties of
topological semimetals

D.A. Pshenay-Severin, Y.V. Ivanov, A.T. Burkov

Ioffe Institute, Peter the Great St.Petersburg Polytechnic University

d.pshenay@mail.ru

Invited talk

The talk gives an overview of the transport properties
of semimetallic materials with a topologically nontrivial band structure. In
the introduction, the report discusses the concept of the Berry phase and Berry
curvature and their use for topological invariants calculations. Using the
example of a material containing Dirac or Weyl nodes near the Fermi level, we
discuss the main properties that can be expected for topological semimetals.
These include the spin-momentum locking and topological protection against
backscattering, the effects of weak antilocalization, the chiral anomaly, the
topological charge and the appearance of Fermi arcs on the sample surface, the
anomalous term in the electron velocity. Next, we discuss the possible
implementations of Weyl and Dirac semimetals in materials with the absence of
time-reversal or inversion symmetry. Using cobalt monosilicide as an example,
“new fermions” with multiple linear band crossing and large
topological charges, as well as their surface states are discussed. An overview
of the experimental data on the transport properties of topological semimetals
is given: negative longitudinal magnetoresistance in TaAs; the Seebeck
coefficient in a longitudinal magnetic field in NbP; high mobility,
magnetoresistance, anomalous Nernst effect and high thermoelectric efficiency
in a magnetic field in Dirac semimetal Cd₃As₂.

Thermoelectric power of
Luttinger liquid

Y. V.
Ivanov, O. N. Uryupin

Ioffe Institute, Russian Academy of Sciences, 194021
St. Petersburg, Russia

yu.ivanov@mail.ioffe.ru

The thermopower of a Luttinger liquid with a potential
barrier is calculated. The long-range nature of the electron-electron
interaction is taken into account. It is shown that an increase of the
interaction range qualitatively changes the temperature dependence of the
thermopower. At low temperatures, the Seebeck coefficient of the Luttinger
liquid is significantly less than the corresponding coefficient of a
one-dimensional Fermi gas. With increasing temperature, the thermopower
increases rapidly and may exceed that of the Fermi gas. The results obtained
are in qualitative agreement with experimental data for quasi-one-dimensional
5-nm-thick InSb wires.

Galvanomagnetic properties
of cobalt monosilicide and compounds based on it

A.Yu. Ovchinnikov, P.P.Konstantinov, D.A. Pshenay-Severin, A.T. Burkov

Peter
the Great St.Petersburg Polytechnic University

graff_icheskiy@mail.ru

Recent
studies of the band structure of cobalt monosilicide (CoSi) revealed
differences from the model commonly used for semimetallic compounds, in which
several parabolic electron and hole bands with some energy overlap are
considered. These differences required to reconsider the approach for
describing the transport properties of these materials used earlier. For this
purpose, several CoSi based samples with the replacement of cobalt atoms by
iron or nickel were studied. The samples contained up to 8 at. % iron and up to
5 at. % nickel. The temperature dependences of the Hall coefficient and the
electrical conductivity of these samples were measured in the temperature range
of 77-800 K. The obtained dependences were analyzed using several models of the
electronic spectrum and carrier scattering.

Effect of V
doping on the Thermoelectric Properties of Fe₂Ti_1-xV_xSn Heusler alloys

A.I. Taranova, A.P. Novitskii, A.I. Voronin, S.V. Taskaev, V.V. Khovaylo

National University of
Science and Technology MISIS

ataranovamisis@gmail.com

The main studies of Fe-based Heusler alloys connected
with magnetic properties, however, some of these alloys are narrow band gap semiconductors.
According to theoretical calculations [1], doping of Fe2TiSn with vanadium can
lead to an increase in the Seebeck coefficient and the power factor. In order
to check the assumptions in this work, the thermoelectric properties of a
series of samples of the composition Fe₂Ti_1-xV_xSn
(x = 0; 0.06; 0.15; 0.2) were investigated.

Polycrystalline Samples were prepared by traditional method using arc
melting technique, the process was carried out in an argon atmosphere. For
homogenization the annealing was carried out for a week at 1073 K in vacuum.
Then arc-melted ingots were ground into powders in a mechanical mortar, and
then by spark plasma sintering (SPS) the pills were obtained. The X-ray phase
analysis confirmed that the entire series of samples was single phase, impurity
phases were missing. However, analysis of the elemental composition revealed
the presence of titanium oxide, as well as areas enriched with titanium and
tin. The thermal stability of samples was investigated by thermogravimetric
analysis, structural transformations did not occur. According to the results of measurements, the
electrical conductivity and the Seebeck coefficient decrease with increasing
vanadium concentration. The type of conductivity changes from p- to n-type, which
is associated with the introduction of electrons due to doping with vanadium;
the undoped sample of Fe2TiSn has the best thermoelectric properties.

[1] S.Yabuuchi, et.al. / /Applied Physics Express. –
2013. – V. 6. – №. 2. – P. 025504.

The simulation thermoelectric materials densification within spark plasma
sintering on the example of Ge-Si

A.S. Tukmakova¹,
K.L. Samusevich¹, A.V. Novotelnova¹, I.L.
Tkhorzhevsky¹

¹ITMO University, 197101, St. Petersburg, Russia

astukmakova@corp.ifmo.ru

The densification of thermoelectric material within spark plasma sintering
has been simulated. The simulation was based on finite elements method and
implemented in Comsol Multiphysics. The model of mechanical processes was based
on the simulation results published earlier for metal and ceramic powder
materials. The model included plastic and elastic deformation Аdescription, influence of porosity on
electrical, thermal and mechanical properties. The results obtained for
dwelling period are in the agreement with the experiment.

Influence of the
two-dimensionalization of electron transport on the conductivity and
thermoelectric power of thermoelectrics on the basis of layered dichalcogenides
of transition metals with substitutions in anionic and cation subsystems.

A.I. Romanenko , G.E. Yakovleva, V.E. Fedorov, A.Yu. Ledneva, S.B. Artemkina, V.A. Kuznetsov

Nikolaev Institute of Inorganic Chemistry Siberian
Branch of Russian Academy of Science

air@niic.nsc.ru

At temperatures below room temperature, the
temperature dependences of the electrical conductivity and the Seebeck
coefficient of bulk polycrystalline samples of titanium and tungsten
dichalcogenides with partial replacement of the transition metal on niobium and
selenium on sulfur – M1-xNbxSe2-ySy (M = W, Ti) were studied. To create
effective thermoelectric converters, materials with a positive and negative
Seebeck coefficient are needed. We have established that W1-xNbxSe2-ySy has a
positive Seebeck coefficient and Ti1-xNbxSe2-ySy-negative. The
two-dimensionality of the transport properties of conduction electrons is
observed at concentrations of niobium x> 0.1 for W1-xNbxSe2-ySy and for all
compositions of Ti1-xNbxSe2-ySy samples. At room temperature, the Seebeck
coefficient (with the same electrical conductivity) in samples with
two-dimensional electron transport is several times higher than in samples with
a three-dimensional one. This is because in two-dimensional systems the Fermi
energy is less than in three-dimensional systems with the same values of
carrier concentration. Calculation of the power factor at room temperature
shows its nine times increase in samples with two-dimensional electron
transport.

The work was supported by the Russian Foundation for
Basic Research (Grant No. 18-503-51017)

Bismuth telluride based
radiation thermopiles obtained by pulsed laser deposition method

A.E. Shupenev¹, I.S. Korshunov²,A.S. Osipkov¹, A.G. Grigoryants¹

¹ Bauman Moscow State Technical University, 105005
Moscow, Russia.

² Joint Institute for High Temperatures (JIHT) RAS, 125412, Moscow, Russia.

ash@bmstu.ru

Radiation thermopiles are basic structures for sensors
used for measuring energy parameters of different radiation with wavelength
from 0.1 to 100 mcm. Current work describes features of using p-Bi_0.5Sb_1.5Te₃
and n-Bi₂Te_2.7Se_0.3 thin film thermopiles
obtained with pulsed laser deposition method on different substrates. Thermal
modeling and experimental research reveal the possibility of achieving
responsivity of 1 V/W and time constant of 10 seconds with the use of polyimide
substrates and absorption zone of 16 mm in diameter

Magnetocaloric effect in zero-applied magnetic fields –a solution to
energy supply problems

N.
Bourobina, D.L. Gregor, G.G. Zegrya

Ioffe Institute

nikabour@mail.ioffe.ru

According to the Global Energy Statistics, published
in 2016, world electricity consumption rebounded after plateauing in 2015.
China and non-Organization for Economic Cooperation and Development were the
main drivers of the rebound in electricity consumption. Central air-conditioning
and refrigeration are a significant component of the electricity consumed.
Air-conditioning power consumption trumps that of most appliances.
Refrigeration technologyis an essential part of civilized human life. Retail
electricity prices tend to increase over time. Thus, improved refrigeration
technology is of major importance and a significant part of any solution to the
current energy crisis. We propose our experimental study of an
environmentally-efficient technology as a contribution to the solution of the
modern energy crisis. The advanced magnetic refrigeration based on the
magnetocaloric effect in zero-applied magnetic fields offers the potential for
high energy efficiency. The strength of our work lies in the substantial change
of the magnetic Curie temperature and the degree of magnetic order in the
La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3-PbTiO3(001) two-phase composite material
through pure voltage control in the absence of external magnetic fields. The
mass-specific isothermal entropy change is larger than 2𝐽/(𝑘𝑔𝐾), which
serves as proof of the principle for the improved refrigeration technology.
Fabrication strategies of the two-phase multiferroics ensembles are also
discussed.

The coherence length and the
quantum size effects’ features in transport phenomena in thin films of bismuth
on substrates of mica

E.V. Demidov, V.M.
Grabov, V.A. Komarov, A.N.Krushelnitckii, A.V. Suslov, M.V.Suslov.

Herzen State Pedagogical University of Russia, 191186, St.Petersburg,
Russia

demidov_evg@mail.ru

Bismuth films are the most suitable objects for the
quantum size effects (QSE) realization: small values of the Fermi energy about
tens of meV, small effective masses about 10^-2m_e, large
values of de Broglie wavelength, about 40 nm for electrons and 10 nm for holes.
Because of QSE, depending on the thickness of the film, the density of charge
carriers’ states has oscillations with a period equal to half carriers’ de
Broglie wavelength, whose amplitude decreases with increasing film thickness.
Because of this, one should expect a similar dependence for the all films’
physical properties determined by the charge carriers’ density of the states.
To form charge carriers’ stationary quantum states it is necessary that the
coherence length of de Broglie waves is not less than the film’s thickness. It
is possible if the charge carriers’ mean free path is not less than the film’s
thickness. Due to this, while studying the quantum size effect, it is important
to determine the coherence length of de Broglie waves and the charge carriers’
mean free path in the studying structures.

Galvanomagnetic coefficients (resistivity,
magnetoresistance, and Hall coefficient) were measured in thin bismuth films on
mica with thickness from 15 to 150 nm at the temperature of 77K. Also we
observed oscillation dependences of the galvanomagnetic properties from the
film thickness for samples with the thickness less than 50 nm. The coherence
length of charge carriers’ de Broglie waves is estimated. The reasons for the
deviation of the observed experimental dependences from the simple quantum size
effect theory in semimetallic films are discussed.

This work was supported by the Minobrnauki of Russia
(as part of the state assignment, project № 3.4856.2017/8.9) and Russian
Foundation for Basic Research, grant № 18-32-00242.

Production of thermoelectric
generators by dispenser printing and laser sintering

M.Greifzu, R.Tkachov, J.Leisten, L.Stepien, E.Lopez, F.Brückner, C.Leyens.

Fraunhofer Institute for Material and Beam Technology
IWS

moritz.greifzu@iws.fraunhofer.de

In this contribution we present a new process of
producing thermoelectric generators (TEG) from bismuth telluride by additive
manufacturing (AM) through dispenser printing and thermal post-processing by
laser.

The efficient production of TEGs is a constantly
brought up issue since often a considerable amount of manual work is still
included. We used dispenser printing, which builds up structures using paste
feedstock. In comparison to other AM technologies paste feedstock requires less
advanced metal powders.

A paste for dispenser printing of Bi2Te3, either
containing n- or p-type powder (arbitrarily shaped, broad size distribution)
has been developed.

Samples for analysis of the thermoelectric properties
of Seebeck coefficient and electrical conductivity dependent on thermal
post-processing were produced. Among classic oven processes especially laser
sintering was investigated. Electrical conductivity appeared to be a problem
for the printed layers. Thermal processes have a strong influence on the quality
of the thermoelectric characteristics since insulating binder is removed and
sinter-contacts but also cracks in the layers can appear. Laser sintering here
has shown good performance to overcome these problems.

A thermoelectric generator was produced by printing
silver contacts onto alumina and subsequently several layers of Bi2Te3 paste.

The dispenser printing and laser post processing have
the potential to build thermoelectric generators on various substrates and
tools

Synthesis of processable
n-type polymers with reproducible thermoelectric characteristics and their
deposition on flexible substrates

R.Tkachov, L.Stepien, M.Greifzu, O.Guskova, A.Kiriy, F.Brückner, E.Lopez, C.Leyens.

Fraunhofer Institute for Material and Beam Technology
IWS

roman.tkachov@iws.fraunhofer.de

Wireless sensor networks (WSNs) are a useful
technology for active monitoring in residential, industrial and medical
applications. Its widespread implementation requires not only reliable but also
self-sufficient power sources that are capable of providing power to the device
for its entire lifespan. Using of thermoelectric generators (TEGs) for this
purpose is an attractive option due to the availability of low-grade ambient
waste heat sources.

In the past decade, electrically conducting organic
materials and their composites have shown big potential owing to their low-cost
fabrication, ambient atmosphere processability and inherently low thermal
conductivity. But in contrast to p-type organic thermoelectric materials,
n-type polymers have seen slow progress based on their general propensity to
react and degrade in air.

This work focuses on the synthesis of n-type
coordination polymers, preparing of the printable paste and dispense printing
on different flexible substrates. Particularly important, we have established
that the process of partial oxidation, which is necessary for the synthesis of
coordination polymers, can be done in advance at the stage of the monomer’s
synthesis.

The prototype presented in this work demonstrates the
feasibility of deploying a printable power solution for practical wireless
sensor network applications.

Theoretical Study on the
Fluorine Doping for Layered Thermoelectric Materials with LaOBiS2-type
Structures

N.Hirayama, M.Ochi, K.Kuroki.

Osaka University, Japan,
Osaka, Ikeda-shi, 1-23-2-101 Hachioji-icchoume

hirayama@presto.phys.sci.osaka-u.ac.jp

LaOBiS2, which comprises
blocking LaO layers and conductive BiS2 layers, has attracted renewed attention
as a thermoelectric material owing to its low thermal conductivity and moderate
ZT value around 0.36 at 650 K. A previous theoretical study has predicted that
replacing Bi with Sb or S with Se improves the power factor of this compound.
Therefore, LaOSbSe2 is a promising candidate of a high-performance thermoelectric
material with low thermal conductivity and high power factor. However, the
development of LaOSbSe2-based thermoelectric materials is currently hindered by
the difficulty in tuning the carrier via impurity doping. For instance, the
electrical conductivity of LaOSbSe2 doped with F (a general dopant for LaOBiS2)
remains nearly identical to that of the undoped system. This study
theoretically investigates the structural properties of LaOBiS2-type quaternary
compounds (LaOBiS2, NdOBiSe2, LaOBiSe2 and LaOSbSe2) and their influences on F
doping. Our first-principles calculation shows that although all stable
structures are in the monoclinic phase in the absence of F doping, LaOSbSe2
exhibits a larger monoclinic distortion than LaOBiS2. All the examined
compounds are found to become tetragonal as the doping concentration increases.
We will discuss how the structural properties influence the doping ability by
comparing the formation energy of the above compounds.

Optimizing p-type
Mg2Si1-xSnx: insight on the band structure from transport modelling

H.Kamila, A.Sankhla, M.Yasseri, P.Sahu, N.Farahi, E.Müller, T.Dasgupta, J.de Boor

German Aerospace Center

johannes.deboor@dlr.de

Development of Mg2Si based thermoelectric generators
requires both good n- and p-type materials. While n-type Mg2(Si,Sn) materials
have good thermoelectric properties, the corresponding p-types do not. Therefore,
optimizing p-type is highly desired. To this end, we have systematically varied
the Si:Sn ratio experimentally and analyzed the transport data in the framework
of a single parabolic band model. The maximum achievable carrier concentration,
power factor, and dopant efficiency increase with increasing Sn content. We
furthermore find a pronounced dependence of the carrier mobility on
composition. We can show that the observed dependence can be understood
considering acoustic phonon and alloy scattering as well as the dependence of
the hole effective mass on composition. We find a valence band effective mass
decreasing from 2.2 me to 1.1 me as we move from Mg2Si to Mg2Sn and obtain a
deformation potential of Edef = 9 eV and an alloy scattering potential constant
of EAS = 0.5 eV by analyzing the temperature dependent mobility for samples
with different compositions. Using these parameters we can predict, first, an
optimum material zT for x ≈0.4, second, a maximum power factor achieved
for Sn-rich compositions and third, a significant improvement of the
thermoelectric properties of Si-rich compositions if the carrier concentration
is increased beyond what has been shown experimentally so far.

Rapid determination of local
composition in inhomogeneous material systems from backscattered electron image
contrast

M.Yasseri, N.Farahi, K.Kelm, E.Müller, J.de Boor.

German Aerospace Center

johannes.deboor@dlr.de

Quantification of different phases in multiphase
materials and the determination of compositions in material systems with
extended solubility of the components are crucial for the engineering of
material properties. In the field of thermoelectrics, multiphase materials are
of considerable interest due to the additional scattering caused by different
phases, reducing the lattice thermal conductivity and consequently improving
the thermoelectric performance of the material. Size, shape, amount, and
composition of secondary phases need to be assessed and optimized to be able to
tune the material properties. SEM-EDX is the state-of-the-art method for such
phase analysis. It suffers, however, from a low throughput and a limited
spatial resolution. In this work, we demonstrate a simple relation between the
grey value in backscattered electron images and the chemical composition
allowing for a rapid method for phase quantification (with respect to
composition as well as compositional fraction) in quasi-binary multiphase or
wide solubility material systems. Applying this method to Mg2SixSn1-x, the Si
and Sn content of each individual point on the BSE images can be calculated.
The introduced SEM image analysis is much faster compared to EDX mapping as it
requires only two EDX point measurements for calibration. Moreover, it also
provides a superior spatial resolution.

Development of a
ZT-measurement system for thin films plus additional Hall constant
determination in a temperature range from LN2 up to 280°C

V.Linseis, Hans-W.Marx.

LINSEIS Messgeräte GmbH

h.marx@linseis.de

Due to new research efforts
in the field of thermoelectrics with a focus on size effects, there is a
growing need for measurement setups dedicated to samples with small geometrical
dimensions like thin films and nanowires with considerably different physical
properties than bulk material. The characterization of these samples is
important to learn more about their structure and conduction mechanism but also
important for technical applications e.g. in the semiconductor industry. We
report on the development of a new system to simultaneous measure electrical
and thermal conductivity, Seebeck coefficient and Hall constant of thin films
in the temperature range from LN2 up to 280°C. Due to the nearly simultaneous
measurement at only one sample, errors caused by different sample compositions,
thicknesses and heat profiles can be avoided. The system consists of a
structured Si-wafer and a suitable measurement setup. To measure the el. conductivity
and the Hall constant, the wafer owns a four-electrode-structure to use the
Van-der-Pauw method. For the Seebeck measurement an additional temperature
gradient can be applied on a membrane setup. The thermal conductivity can be
measured in plane using the Völklein Method, doing a steady state or
transient measurement. To get a correct result, the measurement has to be done
under vacuum in a thermal stabilized and controlled chamber. In order to meet
these requirements a suitable vacuum chamber with sample holder has been
designed. The sample holder can be cooled with liquid nitrogen and heated by
Joule heating. To measure the Hall constant, the chamber is put between two
spools of an electromagnet to apply a variable magnetic field with a maximum of
± 1 T. As proof of concept, a showcase study of Bi87Sb13 thin films has been
performed and compared to previously published data as well as results for
metallic and organic samples.

Pseudogap Engineering of
Thermoelectric Materials based on Heusler Compound Fe2Val

Y.Nishino

Nagoya Institute of Technology

nishino@nitech.ac.jp

The Heusler-type Fe2VAl-based compounds can be a
possible candidate for new thermoelectric materials. Since the Seebeck
coefficient varies systematically with the valence electron concentration
(VEC), irrespective of doping elements, the net effect of doping is most likely
to cause a rigid-band-like shift of the Fermi level from the central region in
the pseudogap. Further increase in the Seebeck coefficient can be achieved by
doping to the Fe/V off-stoichiometric alloys, because of a favorable
modification in the electronic structure around the Fermi level. Moreover, V/Al
off-stoichiometry causes a large enhancement in the Seebeck coefficient with
both positive and negative signs, in parallel with an increase in the peak
temperature up to 400-600K. The maximum power factor is 4×10-3 W/mK2 for p-type
and 7×10-3 W/mK2 for n-type, both of which are substantially higher than that
reported for ZrNiSn-based half-Heusler compounds, Sb-based skutterudites and
Sb-doped Mg2Si in the same temperature range. It is also shown that the heavy
element Ta substitution combined with the V/Al off-stoichiometric effect leads
to a large increase in the dimensionless figure of merit ZT. Further,
high-pressure torsion (HPT) processing is effective in reducing the thermal
conductivity to about 5.0 W/mK because of the presence of ultra-fine grained
structure, while retaining the large power factor, so that ZT = 0.30 can be
obtained for Fe2VTa0.05Al0.95 at around 500 K.

Stability Studies of
Magnesium Silicide based Compounds under different heat treatment conditions

E.Symeou, C.Nicolaou, J.Giapintzakis, Th.Kyratsi

University of Cyprus

simeou.elli@ucy.ac.cy

In recent years, researchers and industries are
attempting to find solutions for the escalating energy crisis and the
threatening global warming. Τhe huge amount of waste heat generated from several domestic and
industrial processes can be directly converted to electricity by using
thermoelectric devices. Doped magnesium silicides are very promising materials
for application in thermoelectric generators due to their excellent
thermoelectric properties, their abundance and non-toxicity. For practical
thermoelectric applications, apart from high efficiency, a secondary
requirement is excellent thermal stability. Their thermal stability issue needs
to be addressed before the materials can be used in thermoelectric devices. In
this study, Sb- and Bi-doped Mg2Si0.6Sn0.4Gex (x=0, 0.005) solid solutions were
prepared by a two-step solid state reaction method followed by hot press.
Thermal stability study was performed from 300 ºC to 500 ºC, in inert
gas and air atmosphere for 1000 hrs. The results showed that Mg2Si0.6Sn0.4Gex
can be exposed for long periods of time to temperatures up to 500 ºC. The
composition, microstructure and thermoelectric properties of the annealed
samples will be presented.

2D Nanomaterials for
Flexible Thermoelectrics

K.Koumoto, R.Tian, C.L.Wan, L.Miao, H.Lin.

Nagoya Industrial Science Research Institute

koumoto@apchem.nagoya-u.ac.jp

Inorganic/organic hybridization based on 2D
nanomaterials is a promising strategy for constructing flexible thermoelectric
materials that can be applied to energy harvesting in the future IoT society.
We have discovered that TiS2-based intercalation complexes with 2D superlattice
structures demonstrate high thermoelectric performance below 100℃ as well
as mechanical flexibility comparable to certain plastics. A new inexpensive
“LESA” process was developed to produce large-area films by a liquid
solution-based approach, and a prototype thin-film TE module consisted of
n-type TiS2/organics superlattice and p-type PEDOT:PSS polymer conductor
generated a high power density of 2.5 Wm-2 at a temperature gradient of 70K.
Moreover, we proposed a thermal deintercalation method to control the carrier density
of a hybrid superlattice and achieved remarkably high power factor ~900 Wm-1K-2
and ZT~0.24 at 300K.

1. C. L. Wan, R. G. Yang, K. Koumoto et al., Nature
Mater., 14, 622-627 (2015).

2. C. L. Wan, R. G. Yang, K. Koumoto et al., Nano
Lett., 15, 6302-6308 (2015).

3. C. L. Wan, R. Tian, K. Koumoto et al., Nano Energy,
30, 840-845 (2016).

4. R. Tian, C. L. Wan, K. Koumoto, et al., J. Mater.
Chem. A, 5, 564-570 (2017).

5. C. L. Wan, R. Tian, K. Koumoto et al., Nature
Commun., 8, 1024 (2017).

6. R. Tian, C. L. Wan, K. Koumoto, et al., MRS Bull.,
43, 193-198 (2018).

Influence of the antimony
sublayer on the formation of a thin bismuth film and its galvanomagnetic
properties

N.S.Kablukova^{1, 2}, E.S.Makarova³, V.A.Komarov¹, D.D.Efimov¹

1 The Herzen State Pedagogical University of Russia

2 Saint-Petersburg State University of Industral
Technologies and Design

3 ITMO
University

kablukova.natali@yandex.ru

Several years ago, a method was developed for
producing single-crystal films under coating [1]. During research, we found
that when the film thickness is less than 300 nm, bismuth and bismuth-antimony
solid solution is collected in droplets and a conductive film is not formed. If
the substance is collected in drops, then it does not wet the surface on which
it is located. Therefore, to create a single-crystal film using the zone
melting method under the coating, it is necessary to achieve wetting of the
substrate. To improve wetting, it was decided to use a layer of antimony, since
antimony is close to bismuth and is well dissolved in it. Therefore, in them
good mutual wetting.

In the study of recrystallized films, we found that
the layer of antimony during recrystallization does not penetrate into the bulk
of the film. X-ray diffraction analysis showed that the crystal structure of
the film with sublayer is similar to the film without sublayer. The use of an
antimony sublayer with a thickness of 10 nm allowed us to obtain a bismuth single-crystal
film with a thickness of 200 nm, and to conduct its research (Figure 1). The
antimony layer introduces insignificant deviations in the values of resistance,
magnetoresistance, Hall coefficient for single-crystal films, which allows to
consider the film consisting only of bismuth when studying the film-substrate
structure.

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Figure 1.
Resistance (left), magnetoresistance (right) of a thin bismuth film 200 nm
thick with different environments.

We will continue to improve the zone recrystallization
method to obtain ultrathin single-crystal films, which are necessary for the
development of physics of quantum effects and phenomena.

Bibliography:

1. A method of creating on various substrates
single-crystal films of a multicomponent solid solution with a uniform
distribution of components by volume / Grabov V.M. et al. // PATENT FOR
INVENTION, No. 2507317 is registered Bulletin No. 1 of January 10, 2014,
application No. 2012128190, priority of the invention 03.07.2012.

Cryogenic thermoelectric cooler at operating temperature below 90 K

N.A.Sidorenko, Z.M.Dashevsky

Ferrotec Nord Corporation, 109383
Moscow, Russia

sidorenko@ferrotec-nord.com

The possibility of creating thermoelectric (TE)
coolers at operating temperatures T ≤
90 K was considered. For these temperatures it is impossible to use the
standard schema of thermoelement, consisting of two semiconductor legs of n-
and p-type, connected in serial electric circuit. At T ≤ 90 K there is
only an effective thermoelectric (TE)
material of n-type, based on Bi – Sb solid solutions. In this case
thermoelement consists from TE leg of n-type and a passive leg, based on high T_c
superconductor (HTSC).

The design of Peltier cryogenic module is proposed,
where n-legs are on the base of extruded Bi_0.91Sb_0.09
crystals and passive legs are base on HTSC YBa₂Cu₃O_7-x
films on SrTiO₃ substrate. Extruded Bi_0.91Sb_0.09 crystals are carried out in a
liquid under high hydrostatic pressure.

TE properties of Bi_0.91Sb_0.09 crystals were studied:
Seebeck coefficient, electrical conductivity, thermal conductivity,
dimensionless TE figure of merit ZT in
temperature range 60 – 100 K and transverse magnetic field B. A
significant increase of ZT was observed
for B = 0.2 T.

The maximal value of the temperature difference ΔT = 14 K
and the maximum cooling capacity Q_c = 0.4 W were obtained at the hot
side temperature T_h= 80 K, the current I = 6.4 A, the voltage U =
0.10 V and B = 0.2 T.

Effective Bi – Sb crystals
for thermoelectric cooling at temperature Т ≤ 180 К

N.A.Sidorenko, Z.M.Dashevsky

Ferrotec
Nord Corporation, 109383 Moscow, Russia

sidorenko@ferrotec-nord.com

It
is known that single crystals of solid solutions Bi-Sb with Sb content from 7
to 15 at. % and n-type conductivity are the most efficient thermoelectric (TE)
materials at temperatures T ≤ 180 K. However, the low mechanical strength
does not allow the use of these materials in real devices.

The
extrusion methods are widely used in the technology of production of TE
materials with high strength characteristics. For
hardening of Bi
-Sb single crystals the method of extrusion
in a liquid medium under high hydrostatic pressure was used.

The bending
strength σ_b normal to the direction of maximum
TE figure of merit Z was
considered as the strength characteristics of extruded Bi_0.91Sb_0.09 crystals. The TE properties
of extruded Bi_0.91Sb_0.09
crystals were studied: Seebeck coefficient, electrical conductivity and thermal
conductivity in the temperature range 77-200 K.

It is
shown, that extruded Bi_0.91Sb_0.09 crystals at T =
180 K and in magnetic field B = 0.7 T
demonstrate the dimensionless figure of merit ZT
= 0.9 and

σ_b
≥ 26 MPa.

Investigation of
thermoelectric properties of the Heusler alloy composition Fe_1.5TiSb

A.V.Kalugina, A.P.Novitskii, D.Yu.Karpenkov, A.I.Voronin, V.V.Khovaylo

National
University of Science and Technology MISIS

m140147@edu.misis.ru

The present
work is concerned with studying thermoelectric properties of Heusler
intermetallic compound Fe-Ti-Sb system, which promising candidates for thermoelectric
materials for the mid-temperature range.

Fe_1.5TiSb Heusler alloy was
synthesized by using the induction melting method. After induction melting,
annealing was performed to homogenize the composition. The prepared sample was
annealed at 800 ℃ for 72 hours, followed by quenching in cold water. Then
the sample was ground in an agate mortar. The pulverized powders were
consolidated by spark plasma sintering (SPS) process at 800 ℃ under
pressure 50 MPa for 10 minutes in an argon atmosphere. Phase composition
identification was performed by x-ray diffraction (XRD) and the surface
morphology of the samples were determined using scanning electron microscope
(SEM) combined with an energy-dispersive x-ray (EDX). Seebeck coefficient and
electrical resistivity were measured in temperature range from room temperature
to 468 K, the thermal diffusivity also was obtained and the thermal
conductivity was calculated. The results of which showed that the thermal
conductivity decreases with increasing temperature. Measurements of electrical
resistivity and the Seebeck coefficient showed that the values of both
quantities increase with increasing temperature. It was concluded that the
material of this composition is a p-type semiconductor. Thermoelectric figure
of merit values were significantly enhanced as the temperature increased. The
highest thermoelectric figure of merit (zT) was obtained at 468 K and it was
0.16. The tendency of temperature dependence of zT demonstrates an increase in
the thermoelectric figure of merit with increasing temperature.

Influence of Ti_1–xNb_xS_2–ySe_y
samples preparation method on their thermoelectric properties

V.A.Kuznetsov, G.E.Yakovleva, S.B.Artemkina, B.M.Kuchumov, V.E.Fedorov, A.I.Romanenko

Nikolaev
Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia

vitalii.a.kuznetsov@gmail.com

Subject
matter related to influence of different preparation conditions of transition
metal dichalcogenides Ti_1-xNb_xS_2-ySe_y
bulk polycrystalline samples on their thermoelectric properties is considered.
Polycrystalline powder specimens of the dichalcogenides were obtained by high
temperature solid-state synthesis. The powders were pressed into tablets 10 mm
in diameter and 2 mm in thickness with a laboratory hydraulic press at a
pressure of 2000 MPa at room temperature. Part of the tablets were sintered in
the evacuated quartz ampoules at 600, 850 and 950°C. Morphology was studied
with scanning electron microscope TM-3000. It has been shown the crystallites
are predominantly oriented perpendicular to the pressing direction.
Experimental samples were obtained by cutting the tablets both along and across
pressing direction. It has been shown that conductivity increases in more than
10 times after sintering. As for Seebeck coefficient, sintering at 600°C
results to increasing of the coefficient, but sintering at higher temperatures
results to decreasing it. It has been also shown that the value of thermal
conductivity is higher for sintered samples. As a result the figure of merit ZT is higher for the samples sintered at
600°C, that is, at a temperature below the synthesis one, when the grain
boundaries have already been improved, but significant growth of the
crystallites has not occurred yet. The thermoelectric properties were measured
along the crystallites. ZT has the
highest value among the samples for the composition of Ti_0.98Nb_0.02S_1.3Se_0.7
and equal to 0.22.

The work
was supported by the Russian Foundation for Basic Research (Grant no.
18-503-51017).

An influence of sample shape
imperfection on relative tolerance of thermal conductivity measurement during
laser flash method.

A.V.Asach¹, G.N.Isachenko^1,2, A.V.Novotelnova¹, V.E.Fomin^1,¶, K.L.Samusevich¹, I.L.Tkhorzhevsky¹

¹ ITMO University,

197101 St.
Petersburg, Russia

²Ioffe Physicotechnical Institute,
Russian Academy of Sciences,

194021 St.
Petersburg, Russia

vladdisslav.fomin@yandex.ru

Abstract This
work studied sample shape influence on relative tolerance of the thermal
conductivity coefficient evaluation during laser flash method (LFM).

Comsol
Multiphysics software was used to simulate actual LFM process for the graphite,
Mg₂Si_0.4Sn_0.6 and Bi₂Te₃
samples. Samples of the cylindrical shape with plane-parallel sides were
studied.

It was
demonstrated that the value of relative tolerance for the plane-parallel
samples is not more than 2%. For
truncated samples with upper side slope of j= 1.5° relative tolerance does not exceed 3%. The
measurement error rises with an increasing of the sample diameter and angle j.

The simulation of
thermoelectric generators based on magnesium silicide solid solutions mg₂(si-sn)
and high manganese silicide

A.M.Masalimov¹, A.S.Tukmakova¹, G.N.Isachenko^1,2, A.V.Asach¹

¹ ITMO University, 197101 St.
Petersburg, Russia

²Ioffe Physicotechnical Institute,
Russian Academy of Sciences, 194021 St. Petersburg, Russia

alibekmslv@gmail.com

We report about
the simulation of silicide-based thermoelectric generators operating at different
conditions. The comparison of coefficient of performance (COP) and output power
has been done for two types of modules: i) based on Mg₂(Si-Sn) solid
solutions of n– and p-type, and ii) based on Mg₂(Si-Sn)
solid solutions of n-type and high
manganese silicide of p-type. The
second type showed a higher value of COP and output power. The model of
generator with different width of n–
and p-type legs has been presented.
It is shown that such modification can improve the COP by 0,5% in comparison
with generator with the legs of identical geometry.

Galvanomagnetic
properties of the thin block
films of Bi_1-_хSb_х (0≤x≤0.15) on the substrates with different thermal
expansion

V.M. Grabov¹, V.A. Komarov¹, E.V. Demidov¹, S.V. Senkevich², A.V. Suslov¹, M.V. Suslov¹

¹ Herzen State Pedagogical
University, 191186 St.
Petersburg, Russia

² Ioffe Physicotechnical Institute,
Russian Academy of Sciences, 194021 St. Petersburg, Russia

SenkevichSV@mail.ioffe.ru

The results
of the study of the galvanomagnetic properties of thin block films of the
bismuth-antimony system in the composition range from 0 to 15 at.% antimony on substrates with different
temperature expansion in the temperature range from 77 K to 300 K in a magnetic
field up to 0.7 T are presented. Films are obtained by the method of discrete
thermal high vacuum evaporation (10^–5 Torr) at a substrate
temperature of 410 K, followed by annealing at 540 K for 30 minutes. Carrier
concentrations and mobilities are calculated in a two-band approximation. The
coefficient of thermal expansion (CTE) of the substrates covers the region from
1.1 to 45·10^–6 K^–1.

The difference in thermal expansion of the materials of the film and the
substrate leads to the fact that the film is in planar stretching conditions when
CTE of the substrate is less than CTE of the film or planar compression when CTE
of the substrate is greater than CTE of the film. The large influence of plane
strain on the galvanomagnetic properties and parameters of the band structure
of charge carriers is shown. The concentration of charge carriers in films on
substrates with CTE greater than the CTE of the film material is higher than in
films on substrates with CTE less than the CTE of the film material. The
difference in concentration increases with decreasing temperature. A similar
character of the dependence of the carrier concentration on the CTE of the
substrate is retained for films of all the compositions and thicknesses
studied.

With an increase in the antimony concentration, the dependence of the
electron mobility changes only slightly, while the dependences of the holes
mobility acquire a much more complex non-monotonic character.

This work was supported by the Ministry of Education and Science of the
Russian Federation (as part of the state assignment, project No. 3.4856.2017 /
8.9) and the Russian Foundation for Basic Research, grant No. 18-32-00430.

Thermoelectric power of the
thin films of Bi_1-_хSb_х (0≤x≤0.15) on the mica and
polyimide substrates in the temperature range of 77–300K

V.M.Grabov¹, V.A.Komarov¹, E.V.Demidov¹, S.V.Senkevich², A.V.Suslov¹, M.V.Suslov¹

¹ Herzen State Pedagogical
University, 191186 St.
Petersburg, Russia

² Ioffe Physicotechnical Institute,
Russian Academy of Sciences, 194021
St. Petersburg, Russia

mvsuslov@mail.ru

The results of the study of the thermopower of thin
block films Bi_1-xSb_x (0≤x≤0.15) with a
thickness of 100–1000 nm on mica and polyimide substrates in the temperature
range 77–300 K are presented. In the measurement of the thermoelectric power,
the method eliminating distortion of the deformation in the film-substrate
system is used. As a result of the differences in the thermal expansion of the materials of the film and
the substrate, the film on polyimide, are in the state of planar compression,
and the film on mica, in the state of planar strain condition at a
temperature below the film formation temperature.

The effect of film
deformation, due to differences in the thermal expansion of the film and
substrate materials, leads to a different character of the temperature
dependences of the thermopower in bismuth-antimony films on mica and polyimide
substrates. The use of films on substrates with a large thermal expansion leads
to a decrease in the thermopower, especially in the low-temperature region.

It was found that a decrease
in crystallite size markedly increases the thermopower of thin films, while a
decrease in thickness leads to the opposite effect, especially in the
low-temperature region.

The maximum value of
thermopower and power factor corresponds to Bi_0.88Sb_0.12
films on mica and polyimide.

In order to further increase
the thermopower of thin films, it is possible to recommend a reduction in the
crystallite size of block specimens with preservation of the crystal texture
and film thickness on substrates with a CTE less than or equal to the CTE of
the film material.

This work was supported by the
Ministry of Education and Science of the Russian Federation (as part of the
state assignment, project No. 3.4856.2017 / 8.9) and the RFBR, grant No.
18-32-00242.

Band structure of the thin block films of Bi_1-_хSb_х
(0≤x≤0.15) on the substrates with different thermal expansion

V.M.Grabov¹, V.A.Komarov¹, E.V.Demidov¹, S.V.Senkevich², A.V.Suslov¹, M.V.Suslov¹

¹ Herzen State Pedagogical
University, 191186 St.
Petersburg, Russia

² Ioffe Physicotechnical Institute,
Russian Academy of Sciences, 194021 St. Petersburg, Russia

a.v_suslov@mail.ru

The paper
presents the results of calculating the concentration of charge carriers in
bismuth-antimony films in the concentration range from 0 to 15 at.% antimony on substrates with different
thermal expansion coefficients, made on the basis of experimental studies of
the galvanomagnetic properties of films obtained by thermal evaporation in a
vacuum. The difference in the coefficient of thermal expansion (CTE) of the
materials of the substrate and the film leads to a planar deformation of the film along its
plane. The CTE of used substrates
covers the region (1.1–45)·10^–6К^–1 and contains substrates with CTE both larger and smaller than the
bismuth CTE (10.5·10^–6К^–1), due to which the films studied are in a planar compression and planar
strain condition.

A significant increase in charge carrier concentration in films on substrates
with CTE more than the CTE of the film, and a decrease in the concentration in
the case of CTE of the substrate is less than the CTE of the film was found.
This character of the dependence of the carrier concentration on the CTE of the
substrate is retained for films of all thicknesses and compositions studied.
This indicates a significant difference in the mechanism of change in the band
structure, caused by the planar deformation of the film and the introduction of
antimony atoms.

Under the action of planar deformation of thin films, caused by the
difference in temperature expansion of the film and substrate materials, the
position of the conduction band and the valence band of the films changes
relative to their position in a single crystal of a corresponding composition.
An increase in the CTE of the substrate is accompanied by an increase in the
position of the ceiling of the valence band and a decrease in the position of
the bottom of the conduction band with respect to the Fermi level. Reducing the
CTE of the substrate leads to the opposite effect.

Effect of La doping on thermoelectric properties of BiCuSeO oxyselenides

D.S.Pankratova, A.P.Novitskii, I.A.Sergienko, S.V.Novikov, P.P.Konstantinov, A.T.Burkov, V.V.Khovaylo.

National
University of Science and Technology MISIS

dasha31pank@gmail.com

BiCuSeO-based
oxide thermoelectric materials were described in 2010 for the first. Since
that, they have attracted significant attention of scientific society. BiCuSeO
compounds exhibit high chemical and thermal stability at high temperatures. The
crystal structure of BiCuSeO corresponds to the structural type of ZrCuSiAs,
and consist of conducting (Cu₂Se₂)^2- layers alternatively
stacked with insulating (Bi₂O₂)²⁺ layers along
the c axis of the tetragonal cell.
The LaCuSeO compounds crystallize to the same structural type, while the band
gap (2,8 eV) is significantly higher than that of BiCuSeO (0,8 eV). In this
work, the thermal and electrophysical properties were investigated for the
series of the samples with chemical composition Bi_1-xLa_xCuSeO
(x = 0; 0.02; 0.04; 0.06; 0.08).

Bulk samples
of Bi_1-xLa_xCuSeO (x = 0; 0.02; 0.04; 0.06; 0.08) oxyselenides were synthesized by
two-step solid-state reaction followed by spark plasma sintering (SPS). Thermoelectric
properties of the specimens were measured in two directions: parallel and
perpendicular to the applied during SPS pressure. The primary results showed
that the thermal conductivity was not affected by the doping, while the
electrical resistivity and the thermopower (Seebeck coefficient) displayed a
tendency to decrease with respect to the La doping level.

Investigation of
thermoelectric properties of W_1-xNb_xSe_2-yS_y
over a wide range of temperature

G.E.Yakovleva, A.I.Romanenko, A.Yu.Ledneva, A.T.Burkov, P.P.Konstantinov, S.V.Novikov, M.K.Han, S.J.Kim, V.E.Fedorov

Nicolaev
Institute of Inorganic Chemistry,

Ioffe
Institute

galina.yakovleva.91@mail.ru

The
transition metal chalcogenides have a great interest in terms of
thermoelectricity due to low thermal conductivity. But, the materials have a
low charge carrier concentration as typical semiconductor. In this work we
investigated the thermoelectric properties of W_1-xNb_xSe_2-yS_ysolid solutions. The substitution of metal atoms in cationic sublattice
on Nb led to increase of charge carrier concentration. The substitution in
anionic sublattice Se on S led to change in grain size in polycrystalline
compounds. This change influenced on the charge
carrier mobility and thermal conductivity of solid solutions. In this way, varying
the concentration of replacement elements in the cationic and anionic
sublattices, the optimal ratio of elements was found. The best value
among the studied materials has W_0.98Nb_0.02Se_1.7S_0.3.
ZT=0.26 (T=650K).

The work
was supported by the Russian Foundation for Basic Research
(Grant No. 18-503-51017).

Thermoelectric and
galvanomagnetic properties of Bi_2-xSb_xTe_3-ySe_y
layered films

L.N.Lukyanova, O.A.Usov, M.P.Volkov

Ioffe
Institute, Russian Academy of Sciences, St Petersburg 194021, Russia

lidia.lukyanova@mail.ioffe.ru

In the
nanostructured layered n-Bi_2-xSb_xTe_3-ySe_y
films related to topological insulators (TI), the temperature dependences of
the thermoelectric properties and quantum oscillations of the magnetoresistance
in strong magnetic fields were investigated. An increase in the thermoelectric
figure of merit Z in the n-Bi_1.6Sb_0.4Te_2.94Se_0.06
films was obtained in the temperature range of 80–300 K compared to the bulk
material. The mean value <Z> = 3.45 10^-3 K^-1 in the
temperature range T = (80-250) K, Z_max = 3.65 10^-3 K^-1
at 185 K. An increase in Z in the films is associated with a decrease in
thermal conductivity and a small increase in the power factor, which is
determined by growth in the Seebeck coefficient, despite a slight decrease in
electrical conductivity.

From the analysis
of magnetoresistance oscillations, the main parameters of the surface states of
Dirac fermions were determined: cyclotron resonance frequency of oscillations,
Fermi velocity, relaxation time, wave vector, and free path of fermions, whose
contribution to the transport and thermoelectric properties is determined by
the position of the Fermi level.

The features of
the energy dependences of the free paths of Dirac fermions and phonons
determine the growth of the Seebeck coefficient and the decrease in thermal
conductivity in n-Bi_1.6Sb_0.4Te_2.94Se_0.06
films. A weak decrease in the electrical
conductivity due to decrease in the bulk electrical conductivity caused by
defects in the bulk of TI is achieved by optimizing the composition and
concentration of charge carriers in the films.

Surface slip in AV2BVI3 crystals

N.M.Abdullaev, I.T.Mammedova, K.G.Halilova, N.N.Mursakulov, S.B.Bagirov, K.Sh.Kahramanov

Institute of Physics, Baku, 1143, Azerbaijan

nadirabdulla@mail.ru

In thin AV2BVI3 foils of 50-100 nm thick, slip
lines, characteristic of deformation bands, were revealed. In AV2BVI3, curved
slip lines with respect to parallel lines are found. The origin of the
discharge bands in Sb2Te3 and Bi2Te3 can be attributed to the presence of
mechanical barriers lying between parallel slip planes (0001).

A review on Reliability of
TEGs

S.Sattar

Russian Friendship University of Russia

Shekkibuzdar@gmail.com

The increasing environmental crisis and energy burden
are drawing enormous attention towards thermoelectric structures and materials.
The recent attention on thermo-electric materials and generators brought the
pending researches on advance level. In spite of the fact that TEG is over the
odds with inadequate efficiency, as compare to other renewable energy sources,
but still TEG got a wide range of acceptance as an influential technology.
Especially 38 years of continuous operation of the MHW-RTG thrilled a sense of
optimism in TE research field. Many companies, including NASA, are trying to
explore new stable materials, methodologies to improve structural designs and
reliability of the module. The current researches encompass enhancement of
performance, life of the device and reduction in cost. To increase the life of
the TEG module, focus is being dedicated to the reliability of the module
—including long life components, mechanical robustness, metallization and
chemically stable materials. As part of deep space mission, to ensure the
longevity of device, work is being done on mechanical stability and suppression
of sublimation. This paper precisely elucidates the role of reliability in TEG
module and current challenges with an overview to understand potential parameters
which affects reliability of the TEG module. The discussion entails recently
proposed alternative designs, fabrication and life-scaling methods for
improving longevity of the thermoelectric modules.

Thermoelectric properties of In_0.2Ce_0.1Co₄Sb_12.3ribbons, prepared by rapid quenching technique

A.T.Burkov¹, S.V.Novikov¹, X.Tang², Y.Yan², A.S.Orekhov^3,4

¹Ioffe Institute, Politecknicheskaya
26, Saint-Petersburg 194021, Russia.

²Wuhan University of Technology 122
Luoshi Road, Wuhan 430070, China.

³Shubnikov Institute of
Crystallography of Federal Scientific Research Centre «Crystallography and
Photonics» of Russian Academy of Science, 119333 Moscow, Russia.

⁴National Research Centre «Kurchatov
Institute», 123182 Moscow, Russia

S.Novikov@mail.ioffe.ru

The article
presents experimental results on thermoelectric properties of In_0.2Ce_0.1Co₄Sb_12.3alloy, prepared by rapid quenching technique. The initial material,
typically in the form of thin ribbons, has quasi-amorphous structure. Usually, the ribbons are crashed to
powder with subsequent compaction by hot-pressing or spark plasma sintering
techniques. However, the thermoelectric properties of as-prepared ribbons have
been unknown. In this work the thermopower and the electrical resistivity of In_0.2Ce_0.1Co₄Sb_12.3ribbons are studied for the first time at temperatures
from 100 K to 750 K. Temperature stability
range of the quasi-amorphous structure, and the crystallization kinetics
were investigated.

Thermoelectric properties of
cobalt monosilicide and alloys based on it.

A.C. Antonov, S.V. Novikov, D.A. Pshenay-Severin, A.T.Burkov

Ioffe
Institute, Politecknicheskaya 26, Saint-Petersburg 194021, Russia.

antonov.arts@gmail.com

Recent
calculations of the cobalt monosilicide band structure revealed a number of
differences from standard model for semi-metallic compounds with the energy
overlap of parabolic bands for electrons and holes. That required modifications
of previously used methods of describing their transport properties. As the
first step of this work, the samples of cobalt monosilicide and its alloys with
the substitution of cobalt for iron or nickel were studied. The investigation
were made for alloy compositions with iron content up to 10 at. % and nickel up
to 5 at. %. The temperature dependences of the thermopower and electrical
conductivity were measured in the range of 100 – 800 K. The possibility of
theoretical interpretation of temperature and concentration dependences with
the help of different models of the electron spectrum was analyzed.

Abstracts

Thermoelectric performance in rare-earth doped BiCuSeO

Thermoelectric properties of Sb2Te3 nanocomposites

New way of application for thermoelectric energy converters

Thermoelectric generators for small temperature ranges

Materials on the basis of bismuth and antimony tellurides received by rapid melt solidation methods

Materials on the basis of bismuth chalcogenides n-type conductivity received by melt solidification in liquid

Thermoelectric properties of n-Mg2(SiGe)0.8Sn0.2 solid solution.

Investigation of the thermoelectric properties Mg2Si0.8Sn0.2 solid solutions doped with Ca and Sb.

Dimensionless mathematical model of a thermoelectric cooler: dTmax mode

Structure and properties of topological semimetals

Thermoelectric power of Luttinger liquid

Galvanomagnetic properties of cobalt monosilicide and compounds based on it

Effect of V doping on the Thermoelectric Properties of Fe2Ti1-xVxSn Heusler alloys

The simulation thermoelectric materials densification within spark plasma sintering on the example of Ge-Si

Influence of the two-dimensionalization of electron transport on the conductivity and thermoelectric power of thermoelectrics on the basis of layered dichalcogenides of transition metals with substitutions in anionic and cation subsystems.

Bismuth telluride based radiation thermopiles obtained by pulsed laser deposition method

Magnetocaloric effect in zero-applied magnetic fields –a solution to energy supply problems

The coherence length and the quantum size effects’ features in transport phenomena in thin films of bismuth on substrates of mica

Production of thermoelectric generators by dispenser printing and laser sintering

Synthesis of processable n-type polymers with reproducible thermoelectric characteristics and their deposition on flexible substrates

Theoretical Study on the Fluorine Doping for Layered Thermoelectric Materials with LaOBiS2-type Structures

Optimizing p-type Mg2Si1-xSnx: insight on the band structure from transport modelling

Rapid determination of local composition in inhomogeneous material systems from backscattered electron image contrast

Development of a ZT-measurement system for thin films plus additional Hall constant determination in a temperature range from LN2 up to 280°C

Pseudogap Engineering of Thermoelectric Materials based on Heusler Compound Fe2Val

Stability Studies of Magnesium Silicide based Compounds under different heat treatment conditions

2D Nanomaterials for Flexible Thermoelectrics

Influence of the antimony sublayer on the formation of a thin bismuth film and its galvanomagnetic properties

Cryogenic thermoelectric cooler at operating temperature below 90 K

Effective Bi – Sb crystals for thermoelectric cooling at temperature Т ≤ 180 К

Investigation of thermoelectric properties of the Heusler alloy composition Fe1.5TiSb

Influence of Ti1–xNbxS2–ySey samples preparation method on their thermoelectric properties

An influence of sample shape imperfection on relative tolerance of thermal conductivity measurement during laser flash method.

The simulation of thermoelectric generators based on magnesium silicide solid solutions mg2(si-sn) and high manganese silicide

Galvanomagnetic properties of the thin block films of Bi1-хSbх (0≤x≤0.15) on the substrates with different thermal expansion

Thermoelectric power of the thin films of Bi1-хSbх (0≤x≤0.15) on the mica and polyimide substrates in the temperature range of 77–300K

Band structure of the thin block films of Bi1-хSbх (0≤x≤0.15) on the substrates with different thermal expansion

Effect of La doping on thermoelectric properties of BiCuSeO oxyselenides

Investigation of thermoelectric properties of W1-xNbxSe2-ySy over a wide range of temperature

Thermoelectric and galvanomagnetic properties of Bi2-xSbxTe3-ySey layered films

Surface slip in AV2BVI3 crystals

A review on Reliability of TEGs

Thermoelectric properties of In0.2Ce0.1Co4Sb12.3 ribbons, prepared by rapid quenching technique

Thermoelectric properties of cobalt monosilicide and alloys based on it.

News

Thermoelectric performance
in rare-earth doped BiCuSeO

Thermoelectric properties of
Sb₂Te₃ nanocomposites

New way of application for
thermoelectric energy converters

Thermoelectric generators
for small temperature ranges

Materials on the basis of
bismuth and antimony tellurides received by rapid melt solidation methods

Materials on the basis
of bismuth chalcogenides n-type
conductivity received by melt solidification in
liquid

Thermoelectric properties of n-Mg₂(SiGe)_0.8Sn_0.2solid
solution.

Investigation of the
thermoelectric properties Mg₂Si_0.8Sn_0.2 solid
solutions doped with Ca and Sb.

Dimensionless mathematical
model of a thermoelectric cooler: dTmax mode

Structure and properties of
topological semimetals

Thermoelectric power of
Luttinger liquid

Galvanomagnetic properties
of cobalt monosilicide and compounds based on it

Effect of V
doping on the Thermoelectric Properties of Fe₂Ti_1-xV_xSn Heusler alloys

The simulation thermoelectric materials densification within spark plasma
sintering on the example of Ge-Si

Influence of the
two-dimensionalization of electron transport on the conductivity and
thermoelectric power of thermoelectrics on the basis of layered dichalcogenides
of transition metals with substitutions in anionic and cation subsystems.

Bismuth telluride based
radiation thermopiles obtained by pulsed laser deposition method

Magnetocaloric effect in zero-applied magnetic fields –a solution to
energy supply problems

The coherence length and the
quantum size effects’ features in transport phenomena in thin films of bismuth
on substrates of mica

Production of thermoelectric
generators by dispenser printing and laser sintering

Synthesis of processable
n-type polymers with reproducible thermoelectric characteristics and their
deposition on flexible substrates

Theoretical Study on the
Fluorine Doping for Layered Thermoelectric Materials with LaOBiS2-type
Structures

Optimizing p-type
Mg2Si1-xSnx: insight on the band structure from transport modelling

Rapid determination of local
composition in inhomogeneous material systems from backscattered electron image
contrast

Development of a
ZT-measurement system for thin films plus additional Hall constant
determination in a temperature range from LN2 up to 280°C

Pseudogap Engineering of
Thermoelectric Materials based on Heusler Compound Fe2Val

Stability Studies of
Magnesium Silicide based Compounds under different heat treatment conditions

2D Nanomaterials for
Flexible Thermoelectrics

Influence of the antimony
sublayer on the formation of a thin bismuth film and its galvanomagnetic
properties

Effective Bi – Sb crystals
for thermoelectric cooling at temperature Т ≤ 180 К

Investigation of
thermoelectric properties of the Heusler alloy composition Fe_1.5TiSb

Influence of Ti_1–xNb_xS_2–ySe_y
samples preparation method on their thermoelectric properties

An influence of sample shape
imperfection on relative tolerance of thermal conductivity measurement during
laser flash method.

The simulation of
thermoelectric generators based on magnesium silicide solid solutions mg₂(si-sn)
and high manganese silicide

Galvanomagnetic
properties of the thin block
films of Bi_1-_хSb_х (0≤x≤0.15) on the substrates with different thermal
expansion

Thermoelectric power of the
thin films of Bi_1-_хSb_х (0≤x≤0.15) on the mica and
polyimide substrates in the temperature range of 77–300K

Band structure of the thin block films of Bi_1-_хSb_х
(0≤x≤0.15) on the substrates with different thermal expansion

Investigation of
thermoelectric properties of W_1-xNb_xSe_2-yS_y
over a wide range of temperature

Thermoelectric and
galvanomagnetic properties of Bi_2-xSb_xTe_3-ySe_y
layered films

A review on Reliability of
TEGs

Thermoelectric properties of In_0.2Ce_0.1Co₄Sb_12.3ribbons, prepared by rapid quenching technique

Thermoelectric properties of
cobalt monosilicide and alloys based on it.