Exsolution of monoclinic iron zirconate in Fe2O3-x oversaturated with Zr4+

The ZrO2 and alpha-Fe2O3-x powders (1:7 in molar ratio) were sintered at 1200 degrees C and then annealed at 850 degrees C for 4-600 h in air. The specimens were studied by analytical electron microscopy with regard to the precipitation of iron zirconate from alpha-Fe2O3-x oversaturated with Zr4+. Fine and disk-like variants of iron zirconate (Fe:Zr similar to 1:1 in atomic ratio) were found to nucleate on habit plane (10 (1) over bar 4) of the hematite matrix. The iron zirconate possesses monoclinic crystallographic symmetry according to electron diffraction and the shape characteristics after prolonged annealing. The crystallographic relationship between hematite (H) and zirconate (Z) is determined to be [2<(11)over bar>0](H)//[010](Z); [01 (1) over bar 0](H)//[101](Z). Clustering of charge- and volume-compensating defects due to Zr4+ occupying substitutional and interstitial octahedral sites of alpha-Fe2O3-x may play a crucial role on the compound formation.