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

Structural change caused by substitution of Nd for Sm in perovskite (Nd, Sm)AlO₃ was 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 (Nd_x, Sm)AlO₃ were precisely analysed for the phases from x  0.0 to 1.0 with an interval of 0.2. The lattice parameters of a series of RAlO₃ vary systematically with the average ionic radii of , accompanying a structural change from orthorhombic to a trigonal system at around  Å corresponding to average ionic radii of . In orthorhombic phases, deformation of the crystal lattice from its ideal cubic lattice is minimized at around x  0.0–0.2 in (Nd_x, Sm)AlO₃ and increased with increasing average ionic radii of Nd and Sm. The structure changes from orthorhombic to trigonal at around x  0.7.