High-temperature phase transition in lanthanum titanate perovskite La0.64(Ti0.92,Nb0.08)O3

High-temperature phase transition of lanthanum niobium titanate La0.64(Ti0.92,Nb0.08)O3 has been studied using neutron powder diffraction and the Rietveld method. The material is orthorhombic (Cmmm) between 295 and 534 K, while it is tetragonal (P4/mmm) between 637 and 740 K. The anti-phase tilt along the b axis of the oxygen octahedron around Ti and Nb atoms was found to induce the tetragonal-to-orthorhombic phase transition. The angle of the tilt and the b/a ratio of cell parameters decrease with an increase of temperature and become 0° and unity, respectively, at a transition temperature between 534 and 637 K.