Effects of chemical compositions and temperatures on the distortion phenomena observed in perovskite-type structures.

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The relationship between chemical compositions and crystal structures were investigated through the materials surveying of perovskite-type phases. The behaviors of structural changes due to chemical compositions and temperatures were studied mainly on the double-oxide perovskite phases. On the other hand, phase stability conditions of boride perovskite phases were considered based on the boron contents as well as their physical properties such as hardness. Syntheses were performed by solid-solid reaction for double-oxides, and flux and arcmelting methods were used for the syntheses of boride perovskite phases. Crystallographic characterizations were mainly carried out by powder X-ray diffraction using shield tube source, and synchrotron radiation were applied in case of the necessity of high-resolution analyses for peak separations. The results of this research project were briefly summarized as follows :1. Double-oxide perovskite phases : Combination of trivalent rare-earth elements a … More nd Al^<3+>, that of divalent alkali-earth and tetravalent rare-earth elements as well as Zr^<4+>, were considered, and structures and structural changes of their end-member and solid solution phases were investigated. As a result, the phases of BaCeO_3, and BaPrO_3, belong to orthorhombic structures and BaZrO_3 is cubic as reported in literatures. However, BaTbO_3 is concluded to be an orthorhombic structure against the past report to be trigonal (rhombohedral lattice). Furthermore, we found that solid solutions of Ba(Pr_<1-x>, Zr_x)O_3 and Ba(Tb_<1-x>, Zr_x)O_3 show the changes from orthorhombic to cubic structures through trigonal lattice in the compositional range of x=0〜1, and that BaPrO_3 shows a similar structure change by temperature increase. These phenomena should be compared with similar structural change which takes place in the solid solution of (Sm_<1-x>, Nd_x) AlO3 by changing x and/or temperatures. Thus, the perovskite-type structures are controllable by an appropriate selection of A and B ions and a temperature condition.2. Boride perovskite : The relationship between chemical composition and structure stability of RB_<1-x>X_3 (R : Rare- earth, X : Noble metal) were mainly investigated based on the syntheses and crystallographic characterizations. The physical properties such as hardness and anti-oxidation properties were considered as well. New materials with interesting structural and physical properties are prospected by conjunction with extensive surveying of various phases, their stoichiometry and structures. Less