Middle-temperature thermoelectric (TE) materials on the basis of PbTe are currently most actively developed. The properties of these materials, and the ways of increasing their thermoelectric figure of merit (Z) are considered. Reducing the lattice thermal conductivity is one of the most effective ways to increase Z. For this purpose, it is promising to create bulk nanostructured TE materials, in which phonons are scattered in the entire wavelength range of phonons. A promising method of obtaining bulk nanostructured TE materials is spark plasma sintering of nanodispersed powders. At the same time, the highest Z values were achieved with a complex approach and the simultaneous effect of several factors, which increase the efficiency of TE materials.

A nanostructured n-type thermoelectric (TE) material based on lead telluride (PbTe) (doped with 0.2 wt% PbI2 and 0.3 wt% Ni) was fabricated and investigated. Fabricating technology included the synthesis of PbTe by direct alloying of components, the grinding of synthesized PbTe in a planetary ball mill, and the compaction of the nanopowders by spark plasma sintering (SPS). Complex investigations of the structure and composition of powders and nanostructured PbTe and the thermoelectric parameters of nanostructured PbTe were carried out. The particle sizes of the powders ground for 20 and 60 min varied from 36 to 378 nm and from 29 to 210 nm, respectively. The maximum value of dimensionless thermoelectric figure of merit (ZT) = 1.35 for nanostructured PbTe was obtained for a sample compacted by SPS after grinding synthesized PbTe for 60 min, which is 14% higher than ZT for TE material obtained by hot pressing. Recrystallization of crystalline particles during SPS leads to an increase of the grain sizes in nanostructured PbTe by approximately 3 times and the elimination of microdeformations that appear during grinding. Analysis of the temperature dependencies of thermoelectric parameters showed that an increase in ZT for nanostructured PbTe is achieved due to the decrease in lattice thermal conductivity.(c) 2023 Elsevier Ltd. All rights reserved.

In the work, the technology of deposition of thin films of Bi 2 Te 3 was worked out and its thermoelectric and electrophysical characteristics were determined. Measurements of the Seebeck coefficient showed its practically linear temperature dependence. At the same time, its values slightly differ during repeated measurements, which may be due to the relaxation processes in the film. During the first measurement, the temperature dependence of the electrical conductivity after the initial decrease in electrical conductivity is observed to increase with a maximum at a temperature of 105°C. Reheating is accompanied by uniform decrease of electrical conductivity. To estimate the influence of a decrease of electrical conductivity with increasing temperature on the thermoelectric properties of the Bi 2 Te 3 layer in a vertical structure, the power factor was calculated. According to the obtained results, despite the drop of electrical conductivity with increasing temperature, the power factor for repeated measurements has a small deviation from the average value over the entire temperature range.

The purpose of this work was to study the effect of stretching on the properties of thermoelectric material films. The thermoelectric and electrophysical properties of Ge2Sb2Tes thin films were studied at various heat treatment temperatures. The results of measuring the electrophysical and thermoelectric properties of Ge2Sb2Tes thin films showed that the highest value of the power factor, namely 0.13 mW/(m K 2 ), have films heat treated at 260°C. The resistance and Seebeck coefficient of Ge2Sb2Tes thin films were measured before and after mechanical loading. Tensile loads were 2.5; 5; 7; 10 kgf. The results of measurements of the Seebeck coefficient and resistance showed that the highest tensile load that Ge2Sb2Tes thin films can withstand without significant changes in the properties of thin films is 2.5 kgf. The value of the power factor showed that the initial films have power factor about 0.05 mW/m K 2 , after the first loading the value of power factor increased to 0.07 mW/m K 2 , and after the second loading it decreased to 0.056 mW/m K 2 .

In this work, thermoelectric properties of Ge2Sb2Te5 thin films obtained by magnetron sputtering were investigated. Deposition was carried out at room temperature, the thickness of the films was 500 nm. The resistivity, Seebeck coefficient and thermal conductivity of thin films were measured. The resistivity of as-deposited layers was about 3500 Ohm·cm and dropped sharply after annealing at a temperature of 260°C for 30 minutes, which is due to the phase transition of the material. The Seebeck coefficient for the as-deposited films was about 1000 μV/K, and the thermal conductivity was 0.16 W/(m·K). It has been established that the highest power factor of 0.13 mW/(m·K2) have Ge2Sb2Te5 thin films heat treated at 260°C

Promising methods for obtaining thermoelectric materials on the basis of Bi 2 Te 3 and Sb 2 Te 3 for low temperature thermoelectric generators are proposed in this article. Thermoelectric and thermal properties of these materials were investigated in the temperature range from ambient temperature up to 330 °C. Thermal stability of these materials was also analyzed. Thermoelectric figure of merit of obtained materials was determined. The working temperature ranges for each material with maximum values of Z=(2.8-3.2)·10 -3 K -1 were determined. Using differential scanning calorimetry and thermogravimetry, it was established that there are no obvious thermal effects and mass changes of investigated samples during multiple measurements. Thus, the studied materials are thermally stable in the mentioned temperature ranges and can be used in low temperature flexible thermoelectric generators.

The development of flexible thermoelectric generators for energy harvesting from the human body has attracted considerable interest in recent years. This paper presents a fabrication technique of thermoelectric legs by screen-printing of suspensions on the basis of Bi 2 Te 2.8 Se 0.2 (n-type) and Bi 0.5 Sb 1.5 Te 3 (p-type) and binders. Zinc phosphate cement and an aqueous alkaline solution of sodium silicate were used as binders. The thermal, electrophysical, thermoelectric properties of the screen-printed films were investigated. The results of the calculation of ZT are presented.