HIGH-TEMPERATURE X-RAY STUDY OF THE CUBIC TETRAGONAL DIFFUSIONLESS PHASE-TRANSITION IN THE ZRO2-ERO1.5 SYSTEM .1. PHASE-CHANGE BETWEEN 2 FORMS OF A TETRAGONAL PHASE, T'-ZRO2 AND T''-ZRO2, IN THE COMPOSITIONALLY HOMOGENEOUS 14 MOL-PERCENT ERO1.5-ZRO2

The cubic-tetragonal phase transition of 14 mol% ErO1.5-ZrO2 was inves tigated through high-temperature powder X-ray diffraction. A new tetra gonal form without tetragonality, t''-ZrO2, was taken into considerati on, although only two forms of t- and t'-ZrO2 have previously been dis tinguished. The metastable t''-ZrO2, which could be obtained by rapid quenching of 14 mol% ErO1.5-ZrO2 melts, partially changed into t'-ZrO2 through a thermal activation process above 500-degrees-C. The t'-ZrO2 continuously changed into t''-ZrO2 or transformed into cubic phase at about 1200-degrees-C. The t'-t'' change occurred reversibly below 110 0-degrees-C.