Crystallography and microstructural studies of phase transformations in the Dy2O3 system

The crystallography, microstructures, and phase transformation mechanisms in dysprosia (Dy2O3) have been studied. The lattice parameters of B and C phases were refined by x-ray diffraction (XRD). The modulated structures and decomposed structures in the CaO-doped samples were characterized by transmission electron spectroscopy (TEM). A new twin was observed in the modulated B phase. Contrary to the previous studies, the B to C transformation was induced by grinding. The A to B transformation was considered to be ferroelastic and the spontaneous strain was calculated. The major driving force for the B (monoclinic) to C (cubic) transformation is suggested to be the release of lattice strains and cation charge repulsions in the B structure, which is analogous to the β (monoclinic) to γ (orthorhombic) transformation in Ca2SiO4. This transformation can be displacive, if some conditions are provided to overcome the bonding energy of the interlayer oxygens in the B structure. copyright 1998 Materials Research Society