Сr-doped bismuth tantalate pyrochlore: Electrical and thermal properties, crystal structure and ESR, NEXAFS, XPS spectroscopy
Н. А. Жук, Н. А. Секушин, Maria G. Krzhizhanovskaya, Aleksandra V. Koroleva, Anastasiya A. Reveguk, Sergey V. Nekipelov, Danil V. Sivkov, V. P. Lutoev, Б. А. Макеев, В.В. Хартон, A. M. Lebedev, Ratibor G. Chumakov, K.D. Koksharova, A.D. Shpynova
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.