ABSTRACT
The cubic-tetragonal phase transition in ZrO2-X mol% RO1.5 ( https://www.w3.org/1998/Math/MathML"> X = 12 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003421290/07e4de97-c68f-4ca1-95b4-28d8b410031d/content/eq166.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> , 14 for R=Er and Y) prepared by rapid quenching of its melt was investigated mainly by high temperature x-ray diffraction. (1) Three forms existed in the tetragonal phase of ZrO2 solid solutions, t-ZrO2, t’-ZrO2 and t”-ZrO2. The t”-ZrO2 was defined as a tetragonal form which had no tetragonality (axial ratio, https://www.w3.org/1998/Math/MathML"> c / a = l https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003421290/07e4de97-c68f-4ca1-95b4-28d8b410031d/content/eq167.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> ) but had an oxygen ion displacement from the ideal fluorite site. (2) The t”-to-t’ change was isothermal, because there existed an energy barrier between t”- and t’-ZrO2. (3) An isothermal feature was also found in the increase of the tetragonality. (4) The t’-form disappeared at about 1200°C in 14mol%ErO1.5-ZrO2. The t’-to-t” change and/or t”-to-c transition temperatures were found to be about 1425°C and 1400°C in 12mol%ErO1.5- and 12mol%YO1.5- samples, respectively. (5) The t”-t’ and/or t”-c transition temperature existed in the vicinity of the cubic solubility limit within the (c+t) two-phase region in the temperature-composition phase diagram. (6) The tetragonality and the oxygen ion displacement seemed to decrease continuously with temperature in ZrO2-12mol%RO1.5.
