Anomalous low-temperature heat capacity in antiperovskite compounds |
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Affiliation: | 1.Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China;2.University of Science and Technology of China, Hefei 230026, China;3.High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China;4.Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China |
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Abstract: | The low-temperature heat capacities are studied for antiperovskite compounds AXM3 (A=Al, Ga, Cu, Ag, Sn, X=C, N, M=Mn, Fe, Co). A large peak in (C-γT)/T3 versus T is observed for each of a total of 18 compounds investigated, indicating an existence of low-energy phonon mode unexpected by Debye T3 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-γT)/T3 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 AXM3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material (e.g., ZrW2O8, ScF3). |
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Keywords: | low-temperature heat capacity low-energy phonon modes antiperovskite compound negative thermal expansion |
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