Microstructural Evolution of Dy(2)O(3)-TiO(2) Powder Mixtures during Ball Milling and Post-Milled Annealing

The microstructural evolution of Dy(2)O(3)-TiO(2) powder mixtures during ball milling and post-milled annealing was investigated using XRD, SEM, TEM, and DSC. At high ball-milling rotation speeds, the mixtures were fined, homogenized, nanocrystallized, and later completely amorphized, and the transformation of Dy(2)O(3) from the cubic to the monoclinic crystal structure was observed. The amorphous transformation resulted from monoclinic Dy(2)O(3), not from cubic Dy(2)O(3). However, at low ball-milling rotation speeds, the mixtures were only fined and homogenized. An intermediate phase with a similar crystal structure to that of cubic Dy(2)TiO(5) was detected in the amorphous mixtures annealed from 800 to 1000 °C, which was a metastable phase that transformed to orthorhombic Dy(2)TiO(5) when the annealing temperature was above 1050 °C. However, at the same annealing temperatures, pyrochlore Dy(2)Ti(2)O(7) initially formed and subsequently reacted with the remaining Dy(2)O(3) to form orthorhombic Dy(2)TiO(5) in the homogenous mixtures. The evolutionary mechanism of powder mixtures during ball milling and subsequent annealing was analyzed.