Abstract
The A2(M,M')2O5 systems (A=Ba, Sr, Ca; M2+=Zn, Mg, Cd, Be; M4+'=Zr, Ce, Ti. Hf, Sn) having a brownmillerite-type compositions were prepared by a solid state reaction. X-ray diffraction analyses confirmed that only the combinations of (Ba-Zn-Zr), (Ba-Zr-Ce), (Ba-Zn-Hf), (Sr-Zn-Zr), (Sr-Zn-Ti) and (Sr-Zn-Hf) for the A-M2+-M4+' in the present systems showed single phases of cubic or orthorhombic perovskite-type structures at room temperature. When the average ionic radii of B site increased, the lattice constants and lattice volumes also increased. Although the samples have the brownmillerite composition, the obtained samples showed perovskite-type structure. The tolerance factor of single phased samples having the brownmillerite composition were estimated to be in the range of 0.9428 ~ 1.0061. It was found that the electrical comductivities of the new phases increased with increasing unit cell free volume.
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