Study urgency and application fields of materials based on oxides of rare-earth elements are discussed. The main investigation results of vaporization processes and the thermodynamic properties in multicomponent systems containing oxides of rare-earth elements are presented. The method of high-temperature mass-spectroscopy and model approaches were used. The need of a further study of the high-temperature behavior of systems containing rare-earth elements is shown to create the national database of thermodynamic properties and models for prediction of physical-chemical properties in oxide systems and materials.