Optimising the structural and ionic conductivity of bismuth tantalate fluorites through rare-earth element doping

Herein, we report a comprehensive study on the chemical modification of Bi₃TaO₇ fluorites through rare-earth element doping to enhance their structural and ionic conductivity. Selected dopants including La³⁺, Nd³⁺, Gd³⁺, Er³⁺ and Yb³⁺ were introduced to replace Ta⁵⁺ for the synthesis of novel solid solutions through solid-state reaction. Despite identical oxidation states and similar ionic radii, the solid solution formation was limited, with secondary phases observed. The lanthanide-doped Bi₃TaO₇ solid solutions exhibited improved ionic conductivity, particularly Bi₃Ta_0.8Nd_0.2O_6.8, which demonstrated the highest conductivity of 9.26 × 10⁻³ S cm⁻¹ at 650 °C. Furthermore, this study highlights the role of oxygen vacancies and crystal defects in enhancing ionic conduction, providing further insights into the development of efficient oxide ionic conductors for applications in solid oxide fuel cells and sensor technologies.