Electron microscopy study of the microstructures in oxygen-deficient pure zirconia and yttrium doped zirconia

The microstructures of oxygen-deficient pure zirconia and 5 mol% Y{dollar}sb2{dollar}O{dollar}sb3{dollar}-ZrO{dollar}sb2{dollar} made by skull melting and/or vacuum sintering have been studied by conventional transmission electron microscopy, high resolution electron microscopy (HREM) and image simulation with multislice calculation.; Oxygen-deficient pure zirconia shows heavy twinning and a high density of stacking faults and dislocations. The atomic nature of the (100) twin interface in monoclinic zirconia has been determined using HREM and simulation. The fault vectors of the stacking faults lying on the (010) plane have been determined to be 1/2(101) or 1/2(101) by g {dollar}cdot{dollar} b analysis and HREM. The stacking faults seem to accomodate part of the nonstoichiometry.; Zirconia that was reduced to a greater extent by vacuum annealing and quenching from 2000{dollar}spcirc{dollar}C has many twinning dislocations at the (100) twin interfaces. The growth tips of the twins have regularly spaced fringes. The HREM study has shown that both of these features are zonal twinning dislocations of height three times d{dollar}sb{lcub}100{rcub}{dollar}. The twin growth has been explained in terms of lattice shearing by zonal twinning dislocations and lattice shuffling. It has also been pointed out that the magnitude of the external shear associated with twinning could be different from that of the internal shear if the twin grows by the movement of zonal twinning dislocations.; The range of microstructural features observed in oxygen-deficient yttria partially stabilized zirconia provides a means to interprete the kinetics of decomposition of the cubic phase. Transmission electron microscopy bright field images show strong tweed contrast, but dark field images with {dollar}{lcub}{dollar}odd, odd, even{dollar}{rcub}{dollar} reflections indicated that the structure is a layered configuration of tetragonal regions, in which each layer is populated by only a single orientational variant with common c axes. Tetragonal microdomains in neighboring layers have a 90{dollar}spcirc{dollar} twin relationship across their interface. The HREM study has revealed antiphase relationships between the tetragonal microdomains in each layer and the existence of the cubic phase between the tetragonal microdomains. For a sample that was cooled less rapidly, the microstructure completely changed to the tetragonal structure with 90{dollar}spcirc{dollar} twins and internal antiphase boundaries. The microstructural development and the kinetics in the cubic-to-tetragonal displacive transformation are discussed.