Crystal structure of Bi{sub 6}Sr{sub 8{minus}x}Ca{sub 3+x}O{sub 22} ({minus}0.5 {le} x {le} 1.7): A mixed valence bismuth oxide related to perovskite
- CSIC, Barcelona (Spain). Inst. de Ciencia de Materials (Spain)
- Univ. of Antwerp (Belgium)
- Univ. de Valencia (Spain)
The crystal structure of Bi{sub 6}Sr{sub 8{minus}x}Ca{sub 3+x}O{sub 22} has been determined by single-crystal X-ray diffraction. This phase is the same as Bi{sub 9}Sr{sub 11}Ca{sub 5}O{sub y} that was previously studied by several authors as a secondary phase in the Bi-Sr-Ca-Cu-O system and coexists in thermodynamic equilibrium with the superconductors Bi{sub 2}Sr{sub 2}CuO{sub 6} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. It crystallizes in the monoclinic space group P2{sub 1}/c, with cell parameters a = 11.037(3) {angstrom}, b = 5.971(2) {angstrom}, c = 19.703(y) {angstrom}, {beta} = 101.46(3){degree}, Z = 2. The structure was solved by direct methods and full-matrix least-squares refinement. It is built up by perovskite-related blocks of composition [Sr{sub 8{minus}x}Bi{sub 2}Ca{sub 3+x}O{sub 16}] that intergrow with double rows [Bi{sub 4}O{sub 6}] running along b. The oxidation of Bi{sub 6}Sr{sub 8{minus}x}Ca{sub 3+x}O{sub 22} at 650 C allows the complete filling of the oxygen vacancies to form the double perovskite (Sr{sub 2{minus}x}Ca{sub x})Bi{sub 1.4}Ca{sub 0.6}O{sub 6} that shows 92.5% of bismuth in +5 oxidation state. The experimental high-resolution electron microscopy image and the electron diffraction pattern of powder samples along the [010] zone axis are in good agreement with those calculated from the structural model obtained by single-crystal X-ray diffraction. The material is almost free of defects and the occurrence of planar defects is very exceptional.
- OSTI ID:
- 638330
- Journal Information:
- Chemistry of Materials, Vol. 10, Issue 7; Other Information: PBD: Jul 1998
- Country of Publication:
- United States
- Language:
- English
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