PEROVSKITE-TYPE (Ndx, Sm1-X)O3: EFFECTS OF INIOC RADII AND TEMPERATURES ON THE STRUCTURE CHANGE. Hiroyuki Horiuchil, AkiraYoshikawa1, Akihiro Saito1, Toetsu Shishido2, Masahiko Tanaka3 and Tsuguo Fukuda2, 1) Mineralogical Inst., Faculty of Science, University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan, 2) Institute for Materials Res., Tohoku University, Katahira, Aoba, Sendai 980, Japan, 3) Photon Factory, National Lab. for High Energy Physics, Oho, Tsukuba, Ibaragi 305, Japan
Effects of the ionic substitution of Nd for Sm on the structure change of perovskite-type (NdX, Sml-x)AIO3 was investigated by means of a high resolution powder X-ray diffraction technique developed by Sasaki et al.1, and the similar structure change which was caused by changing temperatures was also discussed based on the results of high-temperature powder X-ray diffraction experiments. The substitution of Nd for Sm changes the average size of rare earth ions in the structure, as a result, this was effective to the cause for an apparent phase transition from orthorhombic to trigonal structure at around x=0.7. On the other hand,
(NdX, Sml-x)AIO3 showed an actual phase transition from orthorhombic to trigonal structure at the temperature which was intimately related to the amount of ionic substitution. The relationship between phase transition temperature and chemical composition was decided as T(deg.C) = -1075x+795 from the phase transition temperatures of (NdX, Sm1-x)AIO3 for x=0.0, 0.4 and 0.7. This structure change is a kind of a first-order phase transition as suggested by O'Bryan et al.2 for SmAIO3. As a result, the phases of RAIO3 with larger rare-earth ions (R) will be assumed to be higher temperature and/or lower pressure structures compared with those with smaller R ions from structural point of view.
1) S.Sasaki et al.(l992) Rev. Sci. Instrum. 63, 1047-1050.
2) O'Bryan et al. (1990) Jour. Mater. Res., 5, 183-189.