The microstructure and thermoelectric properties of a Bi2Te3–Bi2Se3 solid solution samples containing 20 mol. % Bi2Te3 doped with Hg2Cl2 of n-type conductivity obtained by hot pressing, extrusion and spark plasma sintering of powders prepared by melt spinning and grinding the ingot in a ball mill were studied. Optical and electron scanning microscopy methods were used. The effect of the disk rotation speed on the morphology of particles obtained by melt spinning is investigated. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured at room temperature and in the temperature range 100 – 700 K and the thermoelectric figure of merit was calculated. The samples had anisotropy of electrical conductivity (σ) and thermal conductivity (κ) in the direction perpendicular and parallel to the pressing, the Seebeck coefficient (α) was isotropic. At 300 K anisotropy factors σ┴/σ// ~ 2, κ┴/κ// ~ 2, α┴/α// ~ 1. The highest thermoelectric figure of merit (ZT)max = 1,0 ± 0,1 at ~ 470 K was obtained for extruded samples from powders prepared by grinding the ingot and for hot-pressed samples from powders obtained by melt spinning.

Abstract—The influence of the addition of nanodispersed graphene in an amount of 0.05–0.15 wt

The microstructure and thermoelectric properties of materials based on Bi0,5Sb1,5Te3 solid solutions p-type conductivity and Bi2Te2,4Se0,6 n-type conductivity doped with graphene have been studied. The samples were obtained by spark plasma sintering of powders prepared by melt spinning and crushed in a ball mill together with graphene plates, which were introduced in an amount of 0,05, 0,1 and 0,15 wt. %. Scanning electron microscopy was used to study the composition and microstructure. The p-type conductivity samples had a fine-grained (on the order of hundreds of nanometers) structure with micron-sized tellurium-based eutectic inclusions. The samples of n-type conductivity contained grains with melted edges. Thermoelectric parameters were measured: the Seebeck coefficient, specific electrical conductivity, thermal conductivity at room temperature and in the temperature range of 100 –700 K, and the thermoelectric figure of merit was calculated. When adding 0,15 wt.% graphene plates to a p-type conductivity solid solution, the maximum thermoelectric figure of merit of the material (ZT)max increased by 13% and at 420 K was 1,3. The highest thermoelectric figure of merit (ZT)max = 0,83 at 470 K was obtained for the a n-type conductivity sample doped with 0,1 wt.% graphene plates.

Исследованы свойства образцов твердого раствора Bi 0.5 Sb 1.5 Te 3 р -типа проводимости, полученных горячим прессованием, экструзией и искровым плазменным спеканием порошков, приготовленных спиннингованием расплава и измельчением слитка в вихревой мельнице до частиц порядка сотен микрон и частиц меньше сотен нанометров (механоактивацией). Порошки и сколы образцов изучены на оптическом и растровом электронном микроскопах. Порошки, полученные спиннингованием расплава при оборотах диска 3000 и 5500 об./мин, имели форму пластин толщиной в десятки микрон, состоящих из фрагментов толщиной от единиц до сотен нанометров. Микроструктурный анализ показал присутствие во всех образцах небольшого количества теллура, что подтверждено и результатами микрорентгеноспектрального анализа. Измерены термоэлектрические параметры: коэффициент Зеебека, удельная электропроводность и теплопроводность при комнатной температуре и в интервале 100–700 К. Рассчитаны решеточная составляющая теплопроводности и коэффициент термоэлектрической добротности ZТ . Максимальное значение ZT = 1.0 ± 0.1 при 380 К достигнуто для образцов, полученных искровым плазменным спеканием и горячим прессованием порошков, приготовленных спиннингованием расплава и механоактивацией соответственно.

— We have studied properties of p -type Bi 0.5 Sb 1.5 Te 3 solid solution samples produced by hot pressing, extrusion, and spark plasma sintering of powders prepared by melt spinning and grinding the ingot in a jet mill to a particle size on the order of hundreds of microns or less than hundreds of nanometers (by mechanical activation). The powders and fracture surfaces of the samples have been examined on an optical and a scanning electron microscope. The powders prepared by melt spinning at disk rotation rates of 3000 and 5500 rpm had the form of platelets tens of microns in thickness, consisting of distinct regions ranging in thickness from a few to hundreds of nanometers. Microstructural analysis showed that all of the samples contained a small amount of tellurium, which was confirmed by X-ray microanalysis data. We have measured the thermoelectric parameters (Seebeck coefficient, electrical conductivity, and thermal conductivity) of the materials at room temperature and in the range 100–700 K and calculated their lattice thermal conductivity and thermoelectric figure of merit, ZT . The highest thermoelectric figure of merit, ZT = 1.0 ± 0.1 at 380 K, has been reached in the samples produced by spark plasma sintering and hot pressing of powders prepared by melt spinning and mechanical activation, respectively.

Abstract—The mechanical compressive properties of the materials based on the n-type Bi2Te3–Bi2Se3 (20 mol σ _u^c = 168 MPa (n-type conduction material) and σ _u^c = 133 MPa (p-type conduction material).

A method for the synthesis of ZnSb and β-Zn4Sb3 compounds has been developed, using rapid crystallization of the melt on a rotating disk (melt spinning) to obtain powders. The microstructure and thermoelectric properties of samples obtained by hot pressing of powders prepared by this method are investigated. The microstructure, chips, and composition of the samples were studied using optical and scanning electron microscopes. The nanoscale structure of the grains of the materials obtained has been established. Thermoelectric parameters: Seebeck coefficient, electrical conductivity and thermal conductivity, in the temperature range 300 − 700 K were measured. The coefficient of thermoelectric figure of merit is calculated. The hot-pressed β-Zn4Sb3 samples from granules, prepared by melt spinning had the highest figure of merit ZТ = 1,0 at 600 K.

— We have demonstrated two processes for the synthesis of zinc antimonide powder using rapid melt cooling: melt spinning and cooling in a liquid. The elemental and phase compositions and surface morphology of hot-pressed undoped and 3 wt % In-doped β-Zn 4 Sb 3 samples have been studied by scanning electron microscopy, X-ray diffraction, and optical microscopy, and their Seebeck coefficient, electrical conductivity, and thermal conductivity have been measured in the range 300–700 K. Indium doping has been shown to reduce the lattice thermal conductivity of the material by a factor of 1.5. The 600-K thermoelectric figure of merit of the undoped sample ( ZT = 0.8) is half that of the doped sample ( ZT = 1.5). We have assessed the effect of thermal cycling in the range 300–700 K on the Seebeck coefficient and electrical conductivity of the samples.

We studied the microstructure and the thermoelectric properties of the materials based on p -type germanium telluride doped with copper and bismuth and obtained by hot pressing of three type powders prepared by ingot grinding in a planetary mill, their sizes being from hundreds of microns (0.315-mm cell) to hundreds of nanometers (mechanical activation) and by melt spinning. We studied the microstructure, the chips and the composition of the samples by optical and scanning electron microscopy. By the diffractometric and the micro X-ray phase analyses, we revealed the presence of copper oxide and germanium precipitation in the samples. The samples obtained from the powder prepared by the mechanical activation had the largest number of grains with the sizes less than units of microns. We measured the following thermoelectric parameters of the materials: the Seebeck coefficient and the specific electrical and thermal conductivity within the temperature range of 300–800 K. We calculated the coefficient of thermoelectric efficiency ZT ; the hot-pressed samples obtained from the powders produced by the melt spinning had the highest value: ZT = 1.5 at 600 K.

— We have worked out conditions for the preparation of microcrystalline n -type lead telluride-based materials doped with lead iodide and investigated their microstructure and thermoelectric properties. The materials were prepared by hot-pressing powders produced by grinding an ingot to a particle size on the order of hundreds of microns in a planetary mill and to a particle size under hundreds of nanometers (mechanical activation) and by melt spinning. Fracture surfaces of the hot-pressed samples were examined on an optical and a scanning electron microscope. All of the samples had a nonuniform microstructure, with both small and larger grains present. In the samples prepared from the powders produced by mechanical activation, nanograins were detected. We have measured the Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples at room temperature and in the range 300–800 K and evaluated their lattice thermal conductivity and thermoelectric figure of merit, ZT . Their lattice thermal conductivity was shown to decrease with decreasing grain size. The highest thermoelectric figure of merit, ( ZT ) max = 1.32 at 630 K, was offered by the materials produced from the mechanically activated powder.

We have studied the properties of samples prepared by hot-pressing and extruding granules produced by solidifying molten Pb-doped Sb2Te3–Bi2Te3 solid solutions (24 and 25 mol % Bi2Te3, 0.04 to 0.14 wt % Pb) in a liquid and comminuted in a mortar, cutting mill, or planetary mill. Their microstructure and fractographs have been investigated using an optical and a scanning electron microscope. The results demonstrate that doping with Pb has no significant effect on the compressive strength of the materials, which depends on the sample preparation procedure and is lowest in the case of the samples prepared by hot-pressing granules comminuted in the cutting mill. The highest strength is offered by the samples prepared by extrusion of 25-mm-diameter rods. Doping with Pb increases carrier concentration (reduces the Seebeck coefficient) and shifts the peak in the thermoelectric figure of merit of the materials, (ZT)max, to higher temperatures. The highest thermoelectric figure of merit, (ZT)max = 1.1 ± 0.1, has been obtained at 360 K for the Bi0.5Sb1.5Te3 solid solution doped with 0.05 wt % Pb and prepared by extruding granules comminuted in the planetary mill.

The microstructure, composition, mechanical and thermoelectric properties of samples cut from different sections of a rod with a diameter of 20 mm, a length of 300 mm, extruded from a briquette pressed from granules obtained by crystallization of Bi0.4Sb1.6Te3 solid solution in water were investigated. It was established that the composition of the samples does not change along the length of the rod, while there is a small amount of the second phase (tellurium-based eutectic) is observed both at the beginning and at the end of the rod. A compression test at room temperature showed that the ultimate strength of specimens cut from the end of a rod is ∼10% higher than that of specimens cut from the middle Thermoelectric parameters (electrical conductivity, thermal conductivity, Seebeck coefficient and thermoelectric figure of merit) at room temperature of samples cut from different areas of the rod were σ = 814 ± 55 S/cm, k = 13.2 ± 0.3 W/cm K, α = 234 ± 5 µ V/K, ZT = 0.93-1.12. Measurements of the thermoelectric properties of these samples in the temperature range of 100-600 K showed that the intrinsic conductivity occurs at temperatures above 450 K. The maximum thermoelectric figure of merit ZTmax = 1.2 ± 0.1 was obtained at a temperature of 340 K.

The microstructure, mechanical, and thermoelectric properties of samples of the n -type Bi 2 Te 3 –Bi 2 Se 3 solid-solution samples containing 6, 8, and 10 mol % Bi 2 Se 3 , doped with antimony iodide, cadmium chloride, and hexabromobenzene, are investigated. The samples are formed by hot pressing and the extrusion of granules prepared by melt crystallization in a liquid and ground in a mortar, cutting mill, and ball mill. Measurements are performed at room temperature and in the range of 100–600 K. The formation conditions and compositions of materials with an ultimate compressive strength of ~250 MPa and thermoelectric efficiency of ( ZT ) max = (0.9–1.0) in the temperature range of 320–430 K are found.

AbstractThe microstructure, mechanical, and thermoelectric properties of samples of the n -type Bi_2Te_3–Bi_2Se_3 solid-solution samples containing 6, 8, and 10 mol % Bi_2Se_3, doped with antimony iodide, cadmium chloride, and hexabromobenzene, are investigated. The samples are formed by hot pressing and the extrusion of granules prepared by melt crystallization in a liquid and ground in a mortar, cutting mill, and ball mill. Measurements are performed at room temperature and in the range of 100–600 K. The formation conditions and compositions of materials with an ultimate compressive strength of ~250 MPa and thermoelectric efficiency of ( ZT )_max = (0.9–1.0) in the temperature range of 320–430 K are found.