Abstract
Thermoelectric materials provide a direct transformation of heat into electric energy. Improving the efficiency of thermoelectric material is a complex and individual task for concrete material. Ternary chalcogenides type Tl4Sn(Pb)X3 (X–S,Se,Te) are perspective thermoelectric materials. To improve the thermoelectric figure of merit of a material the reduction of the phonon thermal is used what can be reached by using polycrystalline or single crystal samples.This work is devoted to the development of technological conditions for the crystal growth of Tl4SnS3 compound. Tl4SnS3 are formed in the Tl2S–SnS quasibinary system by peritectic reaction L + Tl2S↔Tl4SnS3 at 626 K and is characterized by polymorphic transformation at 600 K. The low temperature modification of Tl4SnS3 are crystallized in tetragonal system, SG P4/ncc.For the current investigation two samples with ratio 1) 66.67 mol.% Tl2S : 33.33 mol.% SnS (1) and 52 mol.% Tl2S : 48 mol.% SnS (2) were obtained. The 1 sample correspond to stoichiometric composition of Tl4SnS3 compound. The 2 sample correspond to nonstoichiometric composition what lies on the branch of the primary crystallization of high temperature modification of Tl4SnS3.The both synthesis were carried out from high purity elementary components in vacuumed to 0.13 Pa quartz ampoules by one-temperature direct method. The maximal temperature of synthesis 698 K was obtained with heating rate 50 K per hour. Cooling to an experimentally selected annealing temperature of 480 K was carried out with rate 30 K / h. The annealing was carried out during 336 h.The crystals growth of the both samples was carried using "the solution-melt" method in a two-zone furnace (temperature of the melt zone – 698 K, annealing zone – 480 K) in a quartz container with a cone-shaped lower part. Obtained single crystals were without cracks.Results of the microstructural analysis (MSA) indicates that the grown crystals do not contain inhomogeneities. Comparison of the experimentally obtained powder diffraction data with theoretically calculated indicate that a both crystals are single-phase. The calculated cell parameters of the 1 and 2 samples are close and agree with the theoretical data.
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Schedule a callMore From: Scientific Bulletin of the Uzhhorod University. Series «Chemistry»
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