Investigation of structural phase transition behavior of SrZrO3 by thermal analyses and high-temperature X-ray diffraction

Structural phase transitions in SrZrO3, which is the mother phase of proton-conducting oxide, have been investigated with a combination of differential scanning calorimetry (DSC), high-temperature X-ray diffraction and dilatometry. In the DSC curve, reversible thermal anomalies due to phase transition were observed at 769 °C, 846 °C and 1102 °C. The phase transitions have been concluded to be of second-order, first-order and second-order at 769 °C, 846 °C and 1102 °C, respectively. From the baseline shift, the variation of heat capacity at the second-order phase transition, ΔCp, was evaluated to be 8 J/mol K and 5 J/mol K at 769 °C and 1102 °C, respectively. The variation of enthalpy, ΔH, of the first-order phase transition at 846 °C has been estimated to be 58 J/mol. High-temperature X-ray diffraction measurements have revealed that the crystal structure of SrZrO3 varies from orthorhombic distorted perovskite with the space group Pbnm to orthorhombic Ibmm, tetragonal I4/mcm, to ideal cubic perovskite, P m 3 ¯ m with increasing temperature. The transition temperatures were in agreement with those obtained by DSC. The structural phase transitions have also been detected at the above temperatures by dilatometry as anomalies of thermal expansion coefficients. The general form of the linear thermal expansion and the linear thermal expansion coefficients obtained by dilatometry showed fair correspondence with the volume expansion estimated from the results of high-temperature X-ray diffraction.