New Phase Transitions in Perovskite Oxides: BiFeO3, SrSnO3, and Pb(Fe2/3W1/3)1/2Ti1/2O3

This paper reports on two new aspects of oxide perovskites: the first part is devoted to new phase transitions, especially at high temperatures; multiferroics such as BiFeO₃ and Pb–Fe–W–titanate are emphasized but nonmagnetic materials such as SrSnO₃ are included. The work summarized on bismuth ferrite emphasizes its metal–insulator transition near 1200 K (atmospheric pressure) and 47 GPa (room temperature); that on SrSnO₃ emphasizes order–disorder phase transitions; and that on lead–iron tungstate–titanate exhibits a classic second-order ferroelectric phase transition, of which rather few are known in the literature. The second part of the paper presents a discussion of constant phase elements for oxide perovskite ceramics; this is a modern way of characterizing their dielectric relaxation, particularly near phase transition temperatures.