Influence of grain boundaries on the formation of new structural states in simple rare-earth oxides

Changes in the structure of Y$_2$O$_3$, Gd$_2$O$_3$, and Eu$_2$O$_3$ nanocrystalline powders after their compaction into pellets have been investigated. It has been shown that, starting from a certain size and structural quality of crystallites of powder-like samples, which are determined by the annealing temperature and time, the subsequent compaction at a maximal load of 6.4 $\cdot$ 10$^3$ kg/cm$^2$ and additional annealing of prepared pellets lead to the formation of new phase states in them. This result indicates that the energy of grain boundaries noticeably affects the phase states of simple oxides of rare-earth elements.