The strain-driven pyrochlore to "defect fluorite" phase transition in rareearth sesquioxide stabilized cubic zirconias

The relationship between the ordering characteristic of the pyrochlore stru cture type and that characteristic of the "defect fluorite" structure type (immediately on either side of two phase regions separating the two structu re types) in a range of rare eath sesquioxide stabilized cubic zirconias is investigated via electron diffraction and imaging. Systematic structural c hange as a function of composition and relative size of the constituent met al ions is highlighted and a multi-q to single-q = 1/2 [111]* model propose d for the observed pyrochlore to defect fluorite phase transition. Strain i ntroduced into the close-packed {111} metal ion planes of the defect fluori te average structure by the local cation and oxygen vacancy distribution is pointed to as the likely origin of the observed behavior. (C) 2001 Academi c Press