Research of the properties of oxide pyrochlore based on bismuth niobate doped with Co, Mn, Cr cations

Synthetic oxide pyrochlores are characterized by a wide range of unique properties. Multi-element pyrochlores doped with several transition elements are of particular interest in terms of the mutual influence of dopants on each other and on the functional properties of the compound. This paper presents the results of a study of the electrical and optical properties of oxide pyrochlore based on bismuth niobate doped with cobalt, chromium, and manganese cations in equimolar amounts. XPS was used to study the charge state of cations in the oxide pyrochlore Bi 1.73 Mn 1/3 Cr 1/3 Co 1/3 Nb 2 O 9 + δ, synthesized by a solid-phase reaction. The XPS spectral parameters for the multi-element pyrochlore were compared with those of transition element oxides. It was shown that pyrochlore exhibits a characteristic shift of the Bi4f and Nb3d spectra toward lower energies by 0.20 and 0.65 eV, respectively. The cobalt and manganese cations are in a mixed charge state, predominantly with an effective charge of +2 and +3. The Cr2p spectrum is a superposition of the spectra of chromium ions in charge states of +3, +4, and +6. It was also established that the ceramic microstructure is low in porosity, formed by fused grains measuring 2 μm. The band gap for the direct allowed transition is 1.85 eV. At 24 °C, the permittivity of the pure and doped samples in the range of 104 – 106 Hz depends weakly on frequency and is 70 and 80, respectively. The dielectric loss tangent for both samples at 1 MHz is 0.002, and the activation energy for high-temperature conductivity is 0.78 and 0.71 eV, respectively. The obtained results can be used to improve the methodology for using the material as, for example, a photocatalyst in the visible spectrum.