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Synthesis, Superstructure, and Vacancy‐Ordering in 2H‐Cu x Ta 1+ y Se 2 ( x , y = 0.52, 0 and 0.16, 0.08)
Author(s) -
Ali Sk Imran,
Mondal Swastik,
van Smaalen Sander
Publication year - 2015
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201400335
Subject(s) - ampoule , superstructure , crystallography , vacancy defect , crystal structure , bar (unit) , stacking , materials science , single crystal , hexagonal crystal system , crystal (programming language) , analytical chemistry (journal) , chemistry , thermodynamics , physics , computer science , programming language , organic chemistry , chromatography , meteorology
Single crystals of Cu x Ta 1+ y Se 2 were grown by chemical vapor transport. Single crystals of different compositions were obtained at slightly different reaction conditions from mixtures of the reactants of the same nominal composition. It is suggested that different diameters of the ampoules imply different contributions of convection and diffusion to the mass transport, and thus are responsible for different ratios of the amount of Cu, Ta, and Se transported. 2H‐Cu 0.52 TaSe 2 ( x = 0.52, y = 0) is formed in the narrower ampoule (diameter 15 mm). The crystal structure is based on the MoS 2 type of stacking of TaSe 2 layers. Partial ordering of Cu over the tetrahedral sites is responsible for a 2 a 0 × 2 b 0 × c 0 superstructure with hexagonal P $\bar{6}$ m 2 symmetry [ a 0 = 3.468 (1) Å, c 0 = 13.568 (3) Å]. 2H‐Cu 0.16 Ta 1.08 Se 2 ( x = 0.16, y = 0.08) is formed in the wider ampoule (diameter 18 mm). It possesses a NbS 2 ‐type of stacking. A superstructure is not formed, but the presence of Cu and intercalated Ta in alternating van der Waals gaps is responsible for the reduction of symmetry from P 6 3 / mmc to P $\bar{6}$ m 1 [ a 0 = 3.439 (2) Å, c 0 = 12.870 (2) Å]. Single crystals are formed towards the hotter side of the ampoules up to a temperature of 1168 K in both reactions.