Anomalous low-temperature heat capacity in antiperovskite compounds

作者：Guo, Xin-Ge; Lin, Jian-Chao; Tong, Peng^*; Lin, Shuai; Yang, Cheng; Lu, Wen-Jian; Song, Wen-Hai; Sun, Yu-Ping

来源：Chinese Physics B, 2017, 26(2): 026501.

DOI：10.1088/1674-1056/26/2/026501

• low-temperature heat capacity
• low-energy phonon modes
• antiperovskite compound
• negative thermal expansion

The low-temperature heat capacities are studied for antiperovskite compounds AXM(3) (A = Al, Ga, Cu, Ag, Sn, X = C, N, M = Mn, Fe, Co). A large peak in (C-gamma T)/T-3 versus T is observed for each of a total of 18 compounds investigated, indicating an existence of low-energy phonon mode unexpected by Debye T-3 law. Such a peak is insensitive to the external magnetic field up to 80 kOe (1 Oe = 79.5775 A.m(1)). For compounds with smaller lattice constant, the peak shifts towards higher temperatures with a reduction of peak height. This abnormal peak in (C-gamma T)/T-3 versus T of antiperovskite compound may result from the strongly dispersive acoustic branch due to the heavier A atoms and the optical-like mode from the dynamic rotation of XM6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AXM(3) compounds, while it is usually concomitant with negative thermal expansion in open-structure material (e.g., ZrW2O8, ScF3).

• 出版日期2017-2
• 单位中国科学院; 中国科学技术大学; 南京大学