Effect of Doping with Iron and Magnesium on High-Temperature Stability and Physicochemical Properties of Bismuth Tanalates

Bismuth tantalum pyrochlores doped with iron and magnesium atoms were obtained thermally stable up to a temperature of 1140°C: Bi₂Mg_xFe_{1 – x}Ta₂O_{9.5 – Δ} (x = 0–1). The effect of Fe and Mg codoping on their crystal structure has been studied. The unit cell parameter of solid solutions increases uniformly from 10.4871 (2) Å (x = 0) to 10.54607 Å (x = 1). According to the XPS and NEXAFS spectroscopy data, it was found that the ions in these solid solutions are in the charge states Bi(+3), Mg(+2), Fe(+3), Ta(+5 – δ). The dopant atoms iron and magnesium are introduced into the positions of the tantalum atom without distorting the symmetry of the crystal lattice.