Thermal Evolution of BaZrO3 and SrZrO3 Perovskites from 4 K to 773 K : an EXAFS Study at Zr-K Edge

In order to better understand the lattice dynamics of perovskites, we have performed temperature-dependent XAS measurements at Zr-K edge on BaZrO3 and SrZrO3. At ambient temperature, BaZrO3 is cubic, and SrZrO3 orthorhombic. For both compounds, using the FEFF6 code, we modeled the EXAFS and extracted photo-electron-wave phase-shift and scattering amplitude. This procedure allowed us to extract distances and Debye-Waller factors, taking into account photo-electron multiple scattering effects. For several atom shells, we fitted the evolution of the Debye-Waller factors as a function of temperature with Einstein or Debye models. The characteristic temperatures obtained show that differences in dynamic behaviour between the two compounds are mainly due to Ba-Sr substitution and that differences in symmetry play a minor role