Crystal structure, dielectric and thermal properties of cobalt doped bismuth tantalate pyrochlore

A phase-pure pyrochlore of the Bi1.49Co0.8Ta1.6O7.0 composition (space group Fd-3m:2, 10.54051 (3) angstrom, Z = 8 (No. 227)) obtained by the solid-phase synthesis was characterized. It was found that the pyrochlore structure is disordered, bismuth ions are shifted to the 96 g position, and oxygen ions replace the 48f and 32e positions. Co(II) cations are characterized by a mixed placement in the 96 g and 16b positions. The samples have a dense, low-porosity microstructure. According to high-temperature X-ray diffraction data, cobalt pyrochlore is stable up to a temperature of 1080 degrees C. With a further temperature increase, it thermally dissociates with the formation of CoTa2O6. The thermal expansion coefficient increases uniformly and weakly from 3.4 to 7.5 center dot 10(-6) degrees C-1 in the range of 30-1020 degrees C. The electrical properties of the pyrochlore were studied by impedance spectroscopy. No ionic processes in the sample were detected. The Bi1.49Co0.8Ta1.6O7.0 is weakly dependent on temperature and frequency. At RT, the permeability varies in the range of 25-28. The dielectric losses tangent decreases with increasing frequency and at a frequency of 10(6) Hz is equal to similar to 0.005. The conductivity activation energy in the range of 22-450 degrees C is 0.58 eV. (c) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

The composition of Bi1.49Co0.8Ta1.6O7.0 was characterized and found to have a disordered pyrochlore structure with shifted bismuth ions and replaced oxygen ions. The microstructure of the samples was dense and low-porosity. The cobalt pyrochlore was stable up to 1080 degrees C and exhibited uniform thermal expansion coefficient. No ionic processes were detected in the sample, and its electrical properties showed weak dependence on temperature and frequency. The conductivity activation energy was determined to be 0.58 eV in a certain temperature range.