Observation of Two Kinds of Structural Phase Transitions in the Ba2In2 O 5 System

Abstract

Structural phase transitions of at high temperatures were investigated by thermal gravimetric-differential thermal analysis (TG-DTA), dilatometry, and differential scanning calorimetry (DSC). It was revealed that there exist three phases in At ∼910°C, a first-order structural phase transition was observed involving absorption of heat and discrete decrease of volume, which agreed well with the reported order-disorder transition of oxide-ion vacancy. At ∼1070°C, a second-order phase transition involving discrete increase of thermal expansion coefficient was observed. The crystal structures of these three phases of were investigated by means of high-temperature X-ray diffractometry (XRD). The XRD patterns at 900 and 1200°C could be indexed assuming brownmillerite-type orthorhombic and tetragonal crystal structures, respectively. The diffraction pattern obtained at 1000°C could not be explained as ideal cubic perovskite structure with disordered oxide-ion vacancy. High-temperature XRD also revealed that rate of the phase transition at 904°C was low, corresponding to high activation energy of the phase transition estimated by using a Kissinger plot of DTA curves. © 2002 The Electrochemical Society. All rights reserved.