Compositional dependence of expansion and compression behavior of ilmenite

Abstract

High-temperature and high-pressure Raman spectra of ilmenite-type MgX4+O3 (X=Si, Ge, Ti) have been collected up to 773 K, and 31.3, 22.4 and 12.0 GPa, respectively. Temperature and pressure dependence of the force constant of X-O stretching bands revealed that mechanisms of expansion and compression of XO6 octahedra are different in three ilmenites. The tendency is consistent with thermodynamic stability of three ilmenites. From the Raman frequency shifts with temperature and pressure, intrinsic anharmonic effects on isochoric specific heat were elucidated. The anharmonic effects are related to the Debye temperature of three ilmenites.