Studies of transitions in ordered and disordered perovskites: X-ray and Mossbauer scattering experiments

Scattering experiments using Mossbauer gamma rays and X-rays have been performed on ordered and disordered Pb(Sc_0.5Nb_0.5)O₃ (PSN), and Pb(Fe_0.5Nb_0.5)O₃ (PFN) which exists only in a disordered state. All three materials are ferroelectric at room temperature and undergo a change to a paraelectric form close to 100 degrees C. No evidence of an increase in inelastic scattering was found as the transition was approached in any of the materials studied. Rather large differences were found in the magnitude of Debye-Waller factors calculated from integrated intensities obtained using X-rays and Mossbauer gamma rays. These differences arise because part of the atomic displacement from positions of high symmetry is dynamic.