Solid solubility was examined in Zr-doped sapphire and Al-doped yttria-stabilized zirconia (YSZ) single crystals from 1200degrees to 1600degreesC. Specimens were fabricated via ion implantation of single crystals, followed by annealing in air. Secondary ion mass spectroscopy (SIMS) was used to quantify solute redistribution during annealing. Comparison of SIMS results with analytical electron microscopy (AEM) revealed an alumina solubility of 0.2-0.3 wt% in zirconia, and a zirconia solubility of 0.004-0.027 wt% in alumina. Direct imaging of zirconia precipitates revealed that tetragonal zirconia precipitates from supersaturated sapphire with the following orientation relationship: (100)(tetragonal) parallel to (0001)(sapphire) and [0(1) over bar 1 ]tetragonal parallel to [1(2) over bar 10](sapphire).