High-temperature synchrotron X-ray powder diffraction study of the orthorhombic–tetragonal phase transition in lanthanum titanate perovskite La0.68(Ti0.95,Al0.05)O3

We have investigated in situ an orthorhombic (o)–tetragonal (t) phase transition of double perovskite-structured La0.68(Ti0.95,Al0.05)O3 by high-resolution (Δd/d≈0.0002) synchrotron powder diffraction technique. The unit-cell parameters increased continuously with temperature also near the o–t transition point. Good agreement was obtained in the unit-cell parameter values between heating and cooling. These results indicate that the o–t phase transition occurs reversibly and continuously at Tc=350±2 °C. We demonstrate that the present synchrotron X-ray powder diffraction technique is very powerful to determine both the transition temperature of a continuous transformation and precise unit-cell parameters even near the continuous transition point.