Сr-doped bismuth tantalate pyrochlore: Electrical and thermal properties, crystal structure and ESR, NEXAFS, XPS spectroscopy

Abstract

The Bi 1.6 Сr 0.8 Ta 1.6 O 7±Δ pyrochlore was synthesized by the solid-phase method (sp. gr. F d-3m:2 , 10.45523(3) Å, Z = 8). The thermal stability of the pyrochlore in air up to 1140 °C has been established. With increasing temperature (30–1200 °C), the unit cell parameter and the thermal expansion coefficient increase isotropically, although weakly from 10.4413 to 10.5255 Å and 4.6 × 10 −6 to 9.2 × 10 −6 °C − 1 . The electron spin resonance spectrum of the Bi 1.6 Сr 0.8 Ta 1.6 O 7±Δ contains an intense Lorentz-shaped band (g∼2.05) with a width of ΔB PP ∼160 mT. According to X-ray absorption fine structure and X-ray photoelectron spectroscopy, the ions are in the charge states Bi(+3), Ta(+5-δ), Cr(+3). The sample contains shallow traps with a depth of 0.39 eV and deep traps with an energy of 1.7 eV. At temperatures above 400 °C, ion transfer begins to dominate, which is revealed in a decrease in the conductivity activation energy to 0.78 eV.