Temperature dependence of EXAFS Debye-Waller factor in the high pressure perovskite SrGeO3

Abstract

The temperature dependence of EXAFS Debye-Waller factors in SrGeO3 perovskite, which synthesize in a cubic anvil type apparatus under 9GPa and 1000K, was investigated with the cumulant expansion method. The Sr and Ge K-edge EXAFS spectra were measured in transmission mode at various temperatures from 30 to 300K. Effective pair potentials, V(u) =αu2/2, were evaluated by harmonic model, the potential coefficient α for Sr-O, Ge-O, Ge-Sr, Sr-Sr and Ge-Ge distances in SrGeO3 perovskite were 2.6 e/VÅ2, 10.3 e/VÅ2, 6.5 e/VÅ2, 4.3 e/VÅ2 and 8.6 e/VÅ2, respectively. Ge-O bond has the largest value. The coefficients for Sr-O bond and Sr-Sr distances are small values in composition with other cubic perovskite-type compounds. It is suggested that the amorphouszation occurs at relatively lower temperature of 500K in SrGeO3 perovskite because these values are very small. In AII+BIV+O3-type perovskite, the potential coefficient for the bond distance which associated B site atom is larger than that for the others distances and this tendency is also seen in high pressure perovskite such as CaGeO3.