Crystal structure and its role in electrical properties of the perovskite CaPbO{sub 3} synthesized at high pressure
- International Superconductivity Technology Center, Tokyo (Japan). Superconductivity Research Lab.
- National Inst. for Research in Inorganic Materials, Tsukuba, Ibaraki (Japan)
- Univ. of Tsukuba, Ibaraki (Japan). Inst. of Materials Science
The orthorhombic modification of CaPbO{sub 3} was synthesized from a mixture of Ca{sub 2}PbO{sub 4} and PbO{sub 2} at high temperature and high pressure. Its structure was analyzed by Rietveld analysis of neutron diffraction data on the basis of space group Pbnm. It has a distorted perovskite structure of the GdFeO{sub 3} type and a unit cell with dimensions of a = 5.6710 {angstrom}, b = 5.8875 {angstrom}, and c = 8.1495 {angstrom}., The Pb-O bond lengths in each PbO{sub 6} octahedron are comparable to each other, whereas the PbO{sub 6} octahedron tilts around [110]{sub p} and [001]{sub p} axes (p: perovskite subcell) by 18.50 and 20.28{degree}, respectively. These tilt angles, which show great structural distortion in CaPbO{sub 3} containing the smaller Ca{sup 2+} ion, are much larger than corresponding ones in crystal chemically isotypic SrPbO{sub 3}. The electric resistivity of CaPbO{sub 3} at room temperature was as high as 3 {times} 10{sup 3} {Omega}{center_dot}cm, which is in sharp contrast to low resistivities observed in other perovskite-type oxides BaPbO{sub 3} and SrPbO{sub 3}. The high resistivity of CaPbO{sub 3} is explained as gap formation between 2p(O) nonbonding and 6s(Pb)-2p(O) sp{sigma} antibonding bands, which overlap with each other in BaPbO{sub 3}. Solid solutions, where Sr{sup 2+}, La{sup 3+}, Nd{sup 3+}, and Y{sup 3+} ions were partially substituted for Ca{sup 2+} ions, were also prepared to examine structural and electrical properties in perovskites based on BaPbO{sub 3}. Substitution of Sr{sup 2+} for Ca{sup 2+} led to reductions in the distortion and gap energy, whereas that of La{sup 3+}, Nd{sup 3+}, and Y{sup 3+} induced metallic conductivity owing to doping of electron carriers into the antibonding band.
- OSTI ID:
- 338727
- Journal Information:
- Chemistry of Materials, Vol. 11, Issue 3; Other Information: PBD: Mar 1999
- Country of Publication:
- United States
- Language:
- English
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