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.
Keywords:heat capacity, thermal expansivity, high-pressure Raman spectroscopy, Grüneisen parameter, lattice vibrational model calculation, Kieffer model.
Publication Date: 2023-01-25