Lack of Cu3+, Pb4+, and Bi5+ ions in metallic and superconducting oxides

Hegde, M. S. ; Ganguly, P. (1988) Lack of Cu3+, Pb4+, and Bi5+ ions in metallic and superconducting oxides Physical Review Letters, 38 (7). pp. 4557-4561. ISSN 0031-9007

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Official URL: http://prb.aps.org/abstract/PRB/v38/i7/p4557_1

Related URL: http://dx.doi.org/10.1103/PhysRevB.38.4557

Abstract

With a view to understand the oxidation states of metal ions involved in oxide superconductors, oxidation behavior of Cu, Pb, and Bi metals have been studiedi employing x-ray-photoemission and ultraviolet-photoemission spectroscopy. Pb and Bi have distinct 6p (0 to 4 eV) and 6s (7.5 to 10 eV) bands and upon oxidation, only the 6p electrons are ionized forming PbO and Bi2O3 with the simultaneous development of the O2-(2p) band (3 to 7 eV). We show that the 6s band of metals lies below the O2-(2p) band, and hence 6s electrons cannot be ionized to form Pb4+ and Bi4+ as expected in PbO2, BaPbO3, BaBiO3, and BaPb0.75Bi0.25O3. Instead these oxides are stabilized with lower valent O22- along with O2- ions with metals remaining in +2 and +3 states. Similarly, it is shown that the Cu2+(3d) band overlaps with the O2-(2p) band in the YBa2Cu3O6.95 completely and the excess oxygen can be stabilized through lower valent oxide ions instead of Cu3+ AE.

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Source:Copyright of this article belongs to American Physical Society.
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