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 (N d, Sm)AlO3 was analysed by application of high-resolution powder X-ray diffraction using synchrotron radiation. The parallel, well monochrom ated and bright incident X-rays improved the full width at half-maximu m (FWHM) to 0.027 degrees in a wide 2 theta range for the standard Si powder. Applying this high-resolution optical system, the lattice para meters of the solid solution (Nd-x, Sm1-x)AlO3 were precisely analysed for the phases from x = 0.0 to 1.0 with an interval of 0.2. The latti ce parameters of a series of RAlO3 vary systematically with the averag e ionic radii of R3+, accompanying a structural change from orthorhomb ic to a trigonal system at around R3+ = 1.11 Angstrom corresponding to average ionic radii of 0.7Nd(3+) + 0.3Sm(3+). In orthorhombic phases, deformation of the crystal lattice from its ideal cubic lattice is mi nimized at around x = 0.0-0.2 in (Nd-x, Sm1-x)AlO3 and increased with increasing average ionic radii of Nd3+ and Sm3+. The structure changes from orthorhombic to trigonal at around x = 0.7.