Pecularities of antiferroelectric phase transitions in PbZr_0.71 Sn_0.29 O₃ crystal investigated by Mössbauer effect

Abstract

The Mössbauer spectra of 119Sn in PbZr1−xSnxO3 compound were studied from 30 to 300 °C with particular emphasis on the regions of phase transitions. Some changes of the Mössbauer spectrum near the phase transition temperatures were observed, as expected from the change in the crystal structure. The measurements also showed that the Mössbauer fraction considerably drops near the temperature of the phase displacive transition between two antiferroelectric phases (AFE1–AFE2), whereas this drop is considerably smaller at Curie point. Little difference was found in the center shift of the spectrum, indicating that the bonding character is not affected by the phase transitions. The obtained results were interpreted according to Dvorak's suggestion that in antiferroelectrics the frequency over the entire optical branch may soften at particular phase transitions. According to the theory, the mode softening should manifest as a decrease in the Mössbauer–Lamb recoil‐free fraction (f‐factor) due to the increasing vibrational amplitude of the soft mode. Such softening was already observed in Raman scattering measurements in the PbZr1−xSnxO3 single crystals.