标题：Anisotropic thermal anharmonicity of CdSiP2and ZnGeP2: Ab initio calculations
作者：Wei, Lei ;Zhang, Guodong ;Fan, Weiliu ;Li, Yanlu ;Yang, Lei ;Zhao, Xian
作者机构：[Wei, Lei ;Zhang, Guodong ;Yang, Lei ;Zhao, Xian ] State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China;[Li, Yanlu ] De 更多
来源：Journal of Applied Physics
摘要：The anisotropic thermal anharmonicity of CdSiP2and ZnGeP2has been studied by calculating the a- and c-axial Gru¨neisen parameters separately to cast light on the mechanism of anisotropic thermal expansivity of ABC2chalcopyrite compounds. Both the Debye model and lattice dynamics theory were implemented to calculate the axial Gru¨neisen parameters. The variation of shear modulus, calculated from the Debye model, demonstrated normal behavior for ZnGeP2but abnormal behavior for CdSiP2, and was thus assumed to be the most important parameter that determines anisotropic thermal anharmonicity. Using phonon frequency-based lattice dynamics, the axial mode Gru¨neisen parameters were calculated for not only the Γ-point but also for other K-points in the first Brillouin zone. The lowest B1and B2modes of both compounds were found to be new soft modes that were not observed in previous studies of volume-dependent mode Gru¨neisen parameters. The larger magnitude of these soft mode Gru¨neisen parameters of CdSiP2was responsible for its greater abnormal axial thermal anharmonicity in the low-temperature range. The Gru¨neisen parameters became positive at 110 K for CdSiP2and 80 K for ZnGeP2. © 2013 AIP Publishing LLC.