Review of lanthanum orthoniobate-based electrolytes.Structure and proton conductivity

Abstract

In this article, we review the most important scientific works devoted to the study of materials with high proton conductivity, which are of interest as alternative materials for industrial use. It is clear from the findings that most high-temperature proton conductors belong to the class of complex oxide compounds with a perovskite structure or derivatives thereof.
Scientists have investigated the structural-mechanical, electronic and optical properties of LaNbO4 lanthanum orthoniobates, the results of which demonstrate several structural phase transitions depending on temperature and pressure in the sequence from orthorhombic through monoclinic to tetragonal symmetries. The crystal structure of LaNbO4 is found to be significantly more anisotropic in nature compared to the widely studied cubic or rhombic perovskites. Doped LaNbO4 also shows a high-temperature phase transition, which clearly affects proton conductivity. The low-temperature phase of LaNbO4 has also been shown to be monoclinic.
Due to the review of scientific papers on these studies it was found that the materials based on rare-earth metal orthoniobates were the most interesting as they showed excellent proton conductivity at intermediate temperatures (400-900°C) in hydrogen or water-containing atmospheres. Further increase in proton mobility in LaNbO4-based materials was achieved by doping such elements as strontium (Sr), cerium (Ce), ytterbium (Yb), praseodymium (Pr), molybdenum (Mo), magnesium (Mg), copper (Cu) and calcium (Ca) among others. Lanthanum orthoniobate - LaNbO4 (LN) - is a promising candidate as proton conducting electrolytes in the mid-temperature region, with potential applications in solid oxide fuel cells (SHFCs) and hydrogen sensors, so requires further research in this area.