PHASE DIAGRAM OF THE TL2S–GA2S3 SYSTEM AND THE CRYSTAL STRUCTURE OF THE TL2GA20S31 COMPOUND
Journal Title: Праці Наукового товариства ім. Шевченка - Year 2017, Vol 48, Issue
Abstract
Phase equilibria in the Tl2S–Ga2S3 system were investigated using differential-thermal and X-ray phase analysis methods. The existence of TlGaS2 and Tl7Ga3S8 compounds was confirmed. Ternary thallium gallium sulfide TlGaS2 melts congruently at 1165 K. The Tl7Ga3S8 compound is incongruent; it forms in a peritectic process L + TlGaS2↔ Tl7Ga3S8 that takes place at 651 K. A new ternary compound Tl2Ga20S31 was found which is formed by a peritectic reaction L + Ga2S3 ↔ Tl2Ga20S31 at 1240 K. It was determined by X-ray powder method that the compound crystallizes in the cubic structure of MgAgAs type, space group F–43m, lattice parameter a = 0.52000(1) nm. Sulfur atoms in the Tl2Ga20S31 structure occupy the crystallographic site 4c. Cation atoms in its turn occupy defect sites 4a (Ga) and 4d (Tl). The second coordination surrounding of sulfur atoms has cuboctahedron shape which corresponds to sphalerite-type anion sub-lattice in which gallium atoms occupy tetrahedral voids, and thallium atoms are located in octahedral voids, due to their relative size. A small addition (~4 at. % Tl) in heterovalent isoelectron substitution of thallium atoms for gallium results in the formation of a new sulfide with a different type of anion sub-lattice compared to the original structure. Such rebuilding of the crystal structure may be used in the design of new materials with interesting properties.
Authors and Affiliations
Oksana TSISAR, Lyudmyla PISKACH, Oleg PARASYUK, Anatoliy FEDORCHUK, Larysa MARUSHKO, Bogdan KOTUR
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