Structural Change Caused by Substitution of Nd for Sm in (Nd, Sm)AlO3: Application of Synchrotron High-Resolution Powder X-ray Diffraction

Abstract

Structural change caused by substitution of Nd for Sm in perovskite (Nd, Sm)AlO3was analysed by application of high-resolution powder X-ray diffraction using synchrotron radiation. The parallel, well monochromated and bright incident X-rays improved the full width at half-maximum (FWHM) to 0.027° in a wide 2θ range for the standard Si powder. Applying this high-resolution optical system, the lattice parameters of the solid solution (Ndx, Sm_{1-x})AlO3were precisely analysed for the phases fromx = 0.0 to 1.0 with an interval of 0.2. The lattice parameters of a series ofRAlO3vary systematically with the average ionic radii of R^{3+}, accompanying a structural change from orthorhombic to a trigonal system at around R^{3+}=1.11 Å corresponding to average ionic radii of 0.7{\rm Nd}^{3+}+0.3{\rm Sm}^{3+}. In orthorhombic phases, deformation of the crystal lattice from its ideal cubic lattice is minimized at aroundx = 0.0–0.2 in (Ndx, Sm_{1-x})AlO3and increased with increasing average ionic radii of Nd^{3+} and Sm^{3+}. The structure changes from orthorhombic to trigonal at aroundx = 0.7.