Synthesis, Thermodynamic Properties, and Ionic Conductivity of Compounds Based on Bismuth Niobates Doped by Rare-Earth Elements (A Review)

Synthesis methods, thermodynamic and functional properties of compounds based on bismuth niobates doped with rare-earth elements (REEs) are presented. These compounds are promising materials for fuel cells, ceramic oxygen generators, electrocatalysis, etc. As show the data generalized, most compounds have a cubic structure of the δ-form of bismuth oxide, which has the highest ionic conductivity among solid-state ionic conductors. The compounds have high lattice enthalpy and are therefore promising high-energy compounds. The review summarizes studies on the basic thermodynamic characteristics of bismuth niobates doped with rare earth elements. The change in standard enthalpies of formation, lattice enthalpies, and heat capacity when replacing one rare earth element with another is analyzed. It is shown that as the radius of rare earth elements decreases, the standard enthalpies of formation increases and lattice enthalpies increases. The change in ionic conductivity with changes in temperature and rare earth element content has been studied. It has been shown that with increasing temperature and REE content, conductivity increases.