Anomalous low-temperature heat capacity in antiperovskite compounds

• Published in: Chinese physics B 2017-02, Vol.26 (2), p.370-374
• Main Author: 郭新格 林建超 童鹏 蔺帅 杨骋 鲁文建 宋文海 孙玉平
• Format: Article
• Language: English
• Subjects: 低温热容; 声子模式; 外部磁场; 异常; 旋转模式; 晶格常数; 负热膨胀材料; 钙钛矿型化合物
• ISSN: 1674-1056; 2058-3834
• DOI: 10.1088/1674-1056/26/2/026501

The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ 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 k Oe（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- γ 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 X M_6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AX M_3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material（e.g., ZrW_2O_8, Sc F_3）.