L. D. Ivanova

Thermoelectric properties of Bi2Te3-Sb2Te3 single crystals in the range 100–700 K

The electrical conductivity, thermoelectric power, and thermal conductivity of Bi2Te3-Sb2Te3 crystals grown by the floating-crucible technique were measured in the temperature range from 100 to 700 K. The thermoelectric figure of merit of the crystals was evaluated. The effect of crystal composition on these properties was analyzed.

Thermoelectric and mechanical properties of the Bi0.5Sb1.5Te3 solid solution prepared by melt spinning

This paper reports the preparation and characterization of pressed microcrystalline materials based on a p-type Bi0.5Sb1.5Te3 solid solution produced from a melt-spun powder. We have examined the effect of melt spinning conditions (temperature, disk rotation rate, and purity of the inert gas in the heat treatment chamber) on the particle size and morphology of the powders and the microstructure and thermoelectric properties of hot-pressed samples and investigated the mechanical properties (compression and bend tests) of materials prepared by various methods. The thermoelectric properties of the materials (thermopower, electrical conductivity, and thermal conductivity) were studied at room temperature and in the range 100–700 K. The highest thermoelectric figure of merit ZT of the materials prepared by pressing the melt-spun powder was 1.3, whereas the ZT of the materials prepared by the other methods did not exceed 1.1. The higher ZT of the materials studied was due to their lower lattice thermal conductivity and slightly higher thermopower.

Nernst-ettingshausen tensor in Sb2Te3 single crystal

On one Sb2Te3 single crystal, the temperature dependences of all three independent components of the Nernst-Ettingshausen tensor (Qikl) are measured in the temperature range of 85–450 K, all three components being negative. Alongside with the Nernst-Ettingshausen effect, the anisotropy of the Hall (Rikl) and Seebeck (Sij) coefficients and the conductivity (σii) is also investigated. The carried-out analysis of the experimental data on the Nernst-Ettingshausen and Seebeck effects indicates that there is the mixed scattering mechanism with the participation of acoustic phonons and impurity ions, the relative contributions of these mechanisms varying with temperature. In the relaxation-time-tensor approximation, the values of the effective scattering parameter (r) are determined. The obtained values point to the dominant scattering at acoustic phonons in the cleavage plane and to the substantial contribution of charged ions to the scattering along the trigonal axis c3. It is shown that it is possible to explain the major features of experimental data on the Nernst-Ettingshausen effect within the two-valence-band model with the participation of several groups of holes in the transport phenomena.

Extruded thermoelectric materials based on Bi2Te3-Bi2Se3 solid solutions

Extruded n-type materials based on Bi2Te3-Bi2Se3 alloys containing 6 to 40 mol % Bi2Se3 have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100–400 K. Their electrical properties have been compared to those of single-crystal analogs. Compositions have been found at which the extruded materials offer the highest thermoelectric performance in different temperature ranges.

Preparation of thermoelectric materials based on higher manganese silicide

Rhenium-doped higher manganese silicide based materials have been prepared by hot pressing. It has been shown that the pressing temperature of the materials can be lowered by adding titanium as a reductant or by sonication during pressing. The average thermoelectric figure of merit of the materials in the temperature range 600–900 K is Z ≅ 0.7 × 10−3 K−1.

Extruded materials for thermoelectric coolers

We have optimized the compositions of p-type thermoelectric materials based on solid solutions between bismuth and antimony tellurides with high thermoelectric figures of merit in different temperature ranges between 100 and 300 K. The materials have been prepared by extrusion and have been characterized by microstructural analysis. Their thermoelectric properties have been studied in the range 100–400 K.

Bi–Sb Solid Solutions: Potential Materials for High-Efficiency Thermoelectric Cooling to below 180 K

The potential of Bi–Sb solid solutions for use in the n-legs of high-efficiency thermoelectric coolers operating below 180 K was discussed. A magnetothermoelectric miniature cooler comprising a two-stage thermopile and permanent magnets was fabricated. The p-legs of the thermopile were made of doped Sb2Te3–Bi2Te3crystals, and the n-legs were made of Bi–Sb crystals. The cooler showed a high mechanical strength and high efficiency at temperatures between 120 and 180 K. It was tested at hot-junction temperatures between 140 and 200 K in vacuum. At a hot-junction temperature of 180 K, current of 1.9 A, and applied voltage of 0.52 V, the cooler showed a maximum temperature difference of 48 K and a maximum refrigerating capacity of 0.085 W.

Thermoelectric materials based on Sb2Te3-Bi2Te3 solid solutions with optimal performance in the range 100–400 K

We have optimized the compositions of thermoelectric materials based on Sb2Te3-Bi2Te3 solid solutions using Czochralski-grown single crystals. The thermoelectric performance of Sb2Te3-Bi2Te3 solid solutions containing 0–100 mol % Bi2Te3 and Bi2Te3-Sb2Te3-Bi2-Bi2Se3 solid solutions containing 2, 4, or 7 mol % Bi2Se3 has been investigated. The Bi2Se3-doped crystals are found to have higher thermoelectric figures of merit compared to the undoped crystals. The optimal crystal compositions are selected for different temperatures in the range 100–400 K.

Structural Defects in Tin-Doped Antimony Telluride Single Crystals

The structural perfection and homogeneity of Czochralski-grown Sb2Te3and Sb1.96Sn0.04Te3crystals were characterized by transmission electron microscopy and electron probe x-ray microanalysis. The Sb, Sn, and Te core-level and valence-band x-ray photoelectron spectra were measured, and the corresponding binding energies were determined. The effect of Sn doping on the electronic structure and transport properties of the crystals was examined. The crystals were shown to be uniform in Sb : Te ratio and to have a relatively perfect structure. The dislocation density in the crystals was determined by electron microscopy and selective etching. The origin of the moiré patterns observed in electron micrographs was discussed. Sn doping of Sb2Te3was shown to produce no significant shifts of the core levels or changes in the electronic density of states in the valence band.

Crystallization and mechanical properties of solid solutions between bismuth and antimony chalcogenides

Using scanning electron microscopy, we have studied how the conditions of preparation of granules of Sb2Te3–Bi2Te3 and Bi2Te3–Bi2Se3 solid solutions through melt solidification in a liquid influence their morphology, fractographs of fracture surfaces of samples prepared by hot-pressing the granules, and the contents of the major components in the samples. The granules are rounded (solidification in water and liquid nitrogen) or platelike (solidification in water under an excess pressure and in liquid-nitrogen-cooled ethanol) in shape. Fracture surfaces of hot-pressed samples prepared from granules comminuted in a ball mill have a uniform, fine microstructure, with faceted grains several microns in size. Characteristically, samples prepared from granules comminuted in a cutting mill have transgranular layered fractures, with layers up to hundreds of microns in thickness. The mechanical properties of the samples (ultimate strength and relative elongation) have been studied using compression tests at temperatures of 300 and 620 K. The samples experience brittle fracture. Their compression strength σc is 55 ± 12 MPa. With increasing temperature, σc varies only slightly, but at 620 K the samples become more plastic and their relative elongation εb increases by a factor of 2–4. The ultimate strength of hot-pressed samples prepared by uniaxial compression is 20% higher than that of samples prepared by biaxial compression.