Specific heat measurements at low temperatures in K 2 MCl 6 antifluorite crystals

TLDR: In this article, measurements of the specific heat at low temperatures were reported for single-crystal samples of K2ReCl6, K2IrCl6 and K2PtCl6.

Abstract: Measurements of the specific heat at low temperatures are reported for single-crystal samples of K2ReCl6, K2IrCl6, and K2PtCl6 The data for K2IrCl6 give strong evidence that in addition to the well-established antiferromagnetic phase transition occurring at a temperature T N = 301 ± 001 K, a displacive phase transition occurs at T c= 283 ± 002 K Although the compounds are structurally similar, the background specific heats at low temperatures are significantly different A careful analysis of these data plus previous data for K2OsCl6 shows that the reason for the large differences in the lattice specific heats is the presence of low-lying rotary modes A Debye temperature of 911 ± 05 K is deduced and effective rotary mode frequencies of 286, 291, 300, and 379 cm−1 are found for K2ReCl6, K2OsCl6, K2IrCl6, and K2PtCl6, respectively