Discussion on very small temperature dependence of diamond’s elastic constants

Diamond shows high Debye temperature (~2200 K) and small Gruneisen parameter (~1), which represent its small anharmonicity. Therefore, the temperature dependence of elastic constants is very small, preventing accurate measurement. Recently, we measured the temperature dependence of C11 of diamond by using picosecond ultrasonics. [A. Nagakubo et al., Appl. Phys. Lett. 108, 221902 (2016).]. Our results indicate that diamond has a further higher Debye temperature than previous measurements, and we found that elastic constants of high-Debye-temperature materials should be measured over a wide temperature range to extract the Debye temperature and the Gruneisen parameter, accurately. We also calculate the temperature dependence of C11 by an ab-initio method, which agree with our measurement. In this study, we discuss the temperature dependence of other elastic constants. We found that careful consideration is required for bond-bending and bond-stretching resistance to evaluate the temperature dependence of its elastic constants.