High‐Temperature X‐ray Study of the Cubic‐Tetragonal Diffusionless Phase Transition in the ZrO ₂ ─ErO _1.5 System: I, Phase Change between Two Forms of a Tetragonal Phase, <i>t′</i> ‐ZrO ₂ and <i>t″</i> ‐ZrO ₂ , in the Compositionally Homogeneous 14 mol% ErO _1.5 ‐ZrO ₂

Abstract

The cubic‐tetragonal phase transition of 14 mol% ErO 1.5 ‐ZrO 2 was investigated through high‐temperature powder X‐ray diffraction. A new tetragonal form without tetragonality, t″ ‐ZrO 2 , was taken into consideration, although only two forms of t‐ and t′ ‐ZrO 2 have previously been distinguished. The metastable t″ ‐ZrO 2 , which could be obtained by rapid quenching of 14 mol% ErO 1.5 ‐ZrO 2 melts, partially changed into t′ ‐ZrO 2 through a thermal activation process above 500°C. The t′ ‐ZrO 2 continuously changed into t″ ‐ZrO 2 or transformed into cubic phase at about 1200°C. The t′‐t″ change occurred reversibly below 1100°C.