Crystal structures and phase transition in the system SrTiO3-La2/3TiO3

The distribution of A-site cations in the perovskite system LaxSr1-3x/2TiO3 depends on the concentration of La3+ ions and associated vacancies. For small x (xless than or similar to0.2), the substitutions are expected to be random. For xgreater than or equal to0.55, the cations are ordered in such a way that successive layers of A-sites are occupied to greater and lesser degree, and this ordering drives a tetragonal distortion. For x from about 0.3 to 0.5, the X-ray patterns show diffuse peaks indicative of similar ordering, but this is not long-range order and no tetragonal distortion results. The lower temperature structures also exhibit out-of-phase tilting of the TiO6 octahedra, setting in at temperatures varying linearly with composition from 105 K for x = 0, to about 650 K at x = 2/3. (C) 2004 Elsevier Inc. All rights reserved.