Structural and textural study on ZrO2-Y2O3 powders

Microporous ZrO2, ZrO2.2 mol% Y2O3 and ZrO2.5 mol% Y2O3 gels were treated in air and under vacuum at temperatures ranging from 450 to 1300 C. XRD and electron diffraction seem to indicate that both pure and doped ZrO2 gels crystallise in the cubic form of ZrO2. As the treatment time at 450 C increased, or after treatment at higher temperatures, cubic to tetragonal to monoclinic transformations occur, but those are delayed as the Y2O3 content in the sample increases. Under some treatment conditions, cubic and tetragonal phases are also retained to some extent in pure ZrO2. Moreover, a rhombohedral deformation of the cubic cell along the 111 form directions was observed in some crystals of pure ZrO2 samples. Textural degradation takes place in both pure and doped ZrO2, due to particle growth and also the loss of porosity and, therefore, the observed structural stabilisation does not improve textural stability. The differences in the texture of pure and doped samples were related to dehydration and crystal growth processes, and to the properties of primary particles in the gels. 31 refs.