Abstract
Singly doped bismuth-containing pyrochlores have potentially attractive photocatalytic and dielectric properties. Here we report the properties of a multielement pyrochlore phase containing equimolar amounts of 3d transition metals. The mixed-cation pyrochlore oxide with the composition Bi2Co1/3Cu1/3Ni1/3Nb2O9+Δ (sp. gr. Fd \(\overline 3 \) m, a = 10.5378 ± 6 Å) was synthesized by solid-state reaction. The chemical state of the transition metal cations in the pyrochlore oxide was determined by X-ray photoelectron spectroscopy (XPS). Parameters of the Bi 5d, Nb 3d, Co 2p, Ni 2p, and Cu 2p XPS spectra of the mixed-cation pyrochlore phase were compared to those of transition metal oxides. By analyzing the relative intensity of peaks in the Cu 2p spectrum, we evaluated the fractions of Cu(I) and Cu(II) cations. The Bi 4f and Nb 3d spectra of the mixed-cation pyrochlore phase have been shown to be shifted to lower energies by 0.25 and 0.65 eV, respectively. The band gap of the pyrochlore phase for the strongest direct allowed electronic transition is 1.1 eV. The results of this study can be used for improving the technology of multilayer ceramic capacitors and microwave dielectric materials.
