Formation and Transformation of Cubic ZrO ₂ Solid Solutions in the System ZrO ₂ —Al ₂ O ₃

In the system ZrO 2 ‐Al 2 O 3 , cubic ZrO 2 solid solutions containing up to 40 mol% Al 2 O 3 crystallize at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and aluminum alkoxides. The values of the lattice parameter, a, increase linearly from 0.5095 to 0.5129 nm with increasing Al 2 O 3 content. At higher temperatures, the solid solutions transform into tetragonal ZrO 2 and α‐Al 2 O 3 . Pure ZrO 2 crystallizes in the tetragonal form at 415° to 440°C.