Crystal structures, dielectric properties, and phase transitions in Sr2ScGaO5-based brownmillerite ceramics

Abstract

In the present work, the crystal structures and dielectric properties of the Sr2Sc1-xInxGaO5 (x = 0.0, 0.1, 0.2, 0.3) ceramics with the brownmillerite structures were investigated. The ceramics belong to the I2mb polar phases with fully ordered oxygen tetrahedral chains based on the X-ray diffraction and transmission electron microscope results. A typical second-order phase transition from the polar I2mb to non-polar Imma phase is identified by the dielectric properties and Raman analysis. The phase transition temperature increases linearly with the x value in Sr2Sc1-xInxGaO5 ceramics, which is induced by the increased ordering degree of GaO4 tetrahedral chains. The fact that no thermal hysteresis was found in dielectric response during the heating and cooling process along with the Curie-Weiss fitting result confirmed the second-order phase transition in the ceramics. The present work identifies the phase transition temperature in Sr2ScGaO5-based brownmillerite ceramics, and it can be easily adjusted by substituting the cations at the octahedral center in the brownmillerite ceramics.