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

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

Source-reported materials — not catalogue approval

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