Температурно-індуковані фазові переходи структур перовскітів: модель зв’язкової валентності

Abstract

The qualitative crystallochemical model has been developed in order to explain temperature-induced phase transitions observed for a number of perovskite structures ABX3 and their relatives and derivatives. Due to quite different intrinsic bond valences, the A–X and B–X bonds in perovskite structures have substantially different thermal expansion rates; as a result, an increase of temperature leads to a preferential elongation of more labile A–X bonds. Hence, heating a perovskite structure at hand can lead to different critical ratios of A–X and B–X bond lengths, resulting in different perovskite structure types observed at higher temperatures. Additionally, a simplified empirical model has been developed for the relationship between the bond valence and the thermal expansion rate of chemical bonds.