Netsu Sokutei, 50 (1), p. 20, (2023)

特 集 - 高圧力と熱測定・熱分析 -


Determination of Grüneisen Parameter using High-pressure Raman Spectroscopy and Heat Capacity Calculation of Earth’s Mantle Minerals

Measurement temperature ranges of isobaric heat capacities (CP) and thermal expansivities (α) of high-pressure stable materials such as Earth’s mantle minerals are usually limited due to breakdown of the crystal structures, back transformation to lower pressure phases or amorphization by heating at 1 atm. In this study, α and CP at 1 atm and high temperatures were theoretically calculated based on lattice vibrational information. Pressure dependences of vibrational frequencies of the mantle minerals were measured by high-pressure micro-Raman spectroscopy using a diamond anvil cell high-pressure apparatus. Thermal Grüneisen parameter (γth) was determined by weighted average of mode Grüneisen parameters derived from the pressure dependence of the vibrational frequencies. The obtained γth was applied to α calculation using the Grüneisen relation equation. Furthermore, CP was calculated by lattice vibrational model calculation using the Kieffer model, in which the obtained α was used to calculate anharmonic contribution. The calculated CP values show good agreement with the measured ones. The series of calculations of α and CP enables us to make reliable extrapolation of measured CP and α data to higher temperatures than maximum measurement temperature.