Anharmonic effective pair potentials in CaTiO₃, SrTiO₃ and CaGeO₃ perovskite

Abstract

The temperature dependence of EXAFS Debye-Waller factors in CaTiO3, SrTiO3 and CaGeO3 perovskite was investigated with the cumulant expansion method. The CaGeO3 perovskite as an analogue of the Earth's lower-mantle mineral was synthesized in a cubic anvil type apparatus under 10 GPa 1250 K The Ca, Ti and Ge K-edge EXAFS spectra were measured in transmission mode at temperature up to 1100 K The effective pair potentials, V(u)= alpha (u2/2+ beta u3/3!, were evaluated and the Grüneisen parameter were calculated. The potential coefficients alpha and beta for Ti-O bond in CaTiO3 are 6.9 eVA(-2) and -38 eVA(-3), respectively. Those for Ge-O bond in CaGeO3 are 9.8 eVA(-2) and -36 eVA(-3), respectively.