Lattice parameters and structural phase transition of lanthanum titanate perovskite, La0.68(Ti0.95,Al0.05)O3

Lattice parameters and the structural phase transition of Lao.6(Tio.95)Alo.o5)03 have been investigated in situ in the temperature range 301-689 K by the synchrotron radiation powder diffraction (SR-PD) technique. High-angular-resolution SR-PD is confirmed to be a powerful technique for determining precise lattice parameters around a phase-transition temperature. The title compound exhibits a reversible phase transition between orthorhombic and tetragonal phases at 622.3 ± 0.6 K. The foliowing results were obtained: (i) the lattice parameters increased continuously with temperature, while the bla ratio decreased continuously with temperature and became unity at the orthorhombic-tetragonal transition point; (ii) no hysteresis was observed between the latticeparameter values measured on heating and on cooling. Results (i) and (ii) indicate that the orthorhombic-tetragonal phase transition is continuous and reversible. The bla ratio is found to exhibit a more continuous temperature evolution than does the order parameter for a typical second-order phase transition based on Landau theory. (au)