HIGH-TEMPERATURE X-RAY STUDY OF THE CUBIC TETRAGONAL DIFFUSIONLESS PHASE-TRANSITION IN THE ZRO2-ERO1.5 SYSTEM .2. TEMPERATURE DEPENDENCES OF OXYGEN-ION DISPLACEMENT AND LATTICE-PARAMETER OF COMPOSITIONALLY HOMOGENEOUS 12 MOL-PERCENT ERO1.5-ZRO2

The tetragonal-to-cubic phase transition of rapidly quenched 12 mol% E rO1.5-ZrO2 was investigated in situ using high-temperature X-ray diffr action. Rapid quenching of the melt yielded a small oxygen ion displac ement and a small tetragonality, axial ratio c/a. Although the tetrago nality of the as-quenched specimen increased with temperature up to ab out 1000-degrees-C, it became independent of temperature on cooling to room temperature from about 1000-degrees-C and reheating up to 1000-d egrees-C. The tetragonality decreased continuously with temperature ab ove 1000-degrees-C and became unity at about 1400-degrees-C. The atomi c coordination z for the oxygen ion, which expresses the displacement from its ideal site in the fluorite-type structure, increased with tem perature and became 1/4 at about 1400-degrees-C. The tetragonality inc reased with annealing time through a thermal activation, which could e xplain the compositional dependence of the tetragonality in rapidly qu enched ZrO2-RO1.5 samples (R = rare earths).