Thermal Analysis at Low and High Temperature and Evidence of Structural Transition Induced by Praseodymium in SrTiO3

Abstract

To explore the nature of ferroelectric behavior induced by Pr ion in the SrTiO3 ceramic, we brought together a combination of Synchrotron x-ray powder diffraction and thermal analysis. Rietveld analysis shows a clear peak splitting strongly suggesting a cubic-tetragonal structural transition when 15 % Pr substitutes the Sr site. To determine the temperature of the structural instability differential thermal analysis at high temperatures (30-900 °C) and specific heat at low temperatures (2-300 K) were performed. The difference in the heat capacity for Pr doped and undoped samples are very small. A plateau in Cp/T vs T at 110 K is a clear evidence of the competing effect of two kinds of order parameters, one represented by the polarization and the other by the rotation of the oxygen octahedral in the perovskite structure. Upon heating, DTA analysis shows an unexpected single endothermal broad anomaly at about 118 °C. The occurrence of this thermal anomaly could be related to displacive structural contributions providing unambiguous evidence of diffuse phase transition.

Synchrotron X-ray Diffraction Investigation of the Anomalous Behavior of Ice During Freezing of Aqueous Systems

“…Considering the literature reports on the stress-induced peak splitting for non ice systems − and for ice VII, it is reasonable to suggest that the peak splitting observed in our study is a result of strain created during water-to-ice transformation. Indeed, stresses could be expected when growing ice crystals met at the interface with each other or a container wall, because water-to-ice transformation is accompanied by an approximately 10% volume increase.…”

“…In the literature, similar diffraction peak splitting has been reported for a wide range of nonaqueous materials, usually in samples under stress, and commonly attributed to a symmetry lowering. − For Ih, splitting of the 100 and 101 peaks was observed in aqueous solutions of a polymer, poly(ethylene oxide)- block -poly[2-(2-hydroxyethyl)ethylene] . The authors proposed that the polymer modifies the structure of ice toward a more “compressed” structure along the c -axis, presumably by binding of the OH groups of the polymer to the faces parallel to the c -axis.…”