Electrical properties and XPS, NEXAFS characterization of Cu-Cr codoped bismuth tantalate pyrochlore

Phase-pure pyrochlore with the composition Bi1.62Cr1/2Cu1/2Ta2O9+Δ (space group Fd-3m, a = 10.4537(8) Å) was synthesized using the solid-phase synthesis method. The sample is characterized by a porous microstructure formed by partially fused crystallites with an average longitudinal size of 1–2 μm. The charge state of transition element cations in oxide ceramics was studied using ultrasoft X-ray spectroscopy using synchrotron radiation (NEXAFS, XPS). The energy position of the XPS Bi4f, Bi5d and Ta4f, Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) and bismuth(III) oxides by 0.2 and 0.8, respectively. Bismuth and tantalum cations have the same effective charge + (3-δ) and + (5-δ). The NEXAFS Cr2p spectrum of ceramics, according to the main characteristics of the spectrum, practically coincides with the spectrum of Cr2O3 and indicates the content of chromium ions in the oxide ceramics in the form of Cr(III), and according to the nature of the Cu2p spectrum, copper ions are predominantly in the Cu(II) state. The sample exhibits semiconductor properties. At 25 ºС, the relative dielectric permittivity of the sample at 106 Hz is 37, dielectric losses are minimal and amount to 3·10−2. The activation energy for conductivity is 0.40 eV. The electrical behavior of the sample is modeled by equivalent electrical circuits. It is shown that upon heating, the rate of charge transfer processes in the sample increases, and the polarization inhomogeneity of the sample decreases. •Multi-element pyrochlore Bi1.62Cr1/2Cu1/2Ta2O9+Δ has been synthesized.•The charge state of the cations has been studied by ultra-soft X-ray spectroscopy using synchrotron radiation (NEXAFS, XPS).•Bi and Ta cations have an effective charge of + (3-δ) and + (5-δ), Cr and Cu cations (+3) and (+2).•The dielectric permittivity is 37, the dielectric losses are 3·10−2, the activation energy of conductivity is 0.40 eV.•The electrical behavior of the sample is modeled by equivalent electrical circuits.