Characteristic length scale for strain fields around impurity cations in perovskites

Lattice parameters have been determined from high-resolution neutron-powder diffraction data collected as a function of temperature for perovskites in the Pr(1-x)La(x)AlO(3) solid solution in order to determine the influence of La doping on the Imma <-> C2/m transition temperature, T(c)(*). A plateau in T(c)(*) at similar to 150 K extends to x approximate to 0.016 +/- 0.002, followed by a linear reduction with increasing LaAlO(3) content. The plateau is interpreted in terms of a saturation effect such that there is a composition limit below which the strain fields surrounding individual La(3+) ions are isolated in the PrAlO(3) matrix and above which they overlap. On this basis the strain fields are estimated to have diameters of similar to 16-18 A degrees, which appears to be a characteristic length scale for structural relaxation around dopant atoms and other types of local clusters in oxide perovskites.