Phase Equilibria in ZrO₂–Y₂O₃–MnO_t Ternary System at 1673 K

Abstract

The phase equilibria in the zirconia-rich part of the ZrO₂–Y₂O₃–MnO_t ternary system have been investigated at 1673 K in air by high temperature X-ray diffraction. The three phases, the tetragonal ZrO₂ phase, the fluorite-type cubic ZrO₂ phase and the Mn₃O₄ phase, have been detected without any compound. The phase boundaries have been intensively examined using the relation between the lattice parameter and composition. The solubility of MnO_t became larger with increasing Y₂O₃ concentration. In the ZrO₂–MnO_t binary system, 5.4 mol%MnO_t is soluble in ZrO₂, while in the ZrO₂–Y₂O₃–MnO_t ternary system, 10.3 mol%MnO_t dissolves into ZrO₂-6 mol%Y₂O₃. For the ZrO₂-3 mol%Y₂O₃ with dissolved MnO_t, the two phases of the tetragonal ZrO₂ solid solution and the fluorite-type cubic ZrO₂ solid solution are transformed to the single phase of the fluorite-type cubic solid solution as the MnO_t concentration increased. For the ZrO₂ with dissolved MnO_t, however, the single phase of the tetragonal solid solution does not transform even though MnO_t dissolved to its solubility. The transformation caused by the dissolution of MnO_t and the solubility of MnO_t in ZrO₂–Y₂O₃ system were discussed in reference to the cationic radius of the Mn ions.