Ceramics were formed by the addition of magnesia to zirconia in the composition range of 0 to 50 mol %, and these ceramic materials were liquid quenched using an infrared image furnace and a twin roll process. The composition and structure of the liquid-quenched film samples were examined using X-ray diffraction and transmission electron microscopy. The results confirmed the formation of a high-temperature metastable phase (t′-phase) in ZrO₂-9 mol % MgO partially stabilized zirconia (PSZ). The t′-phase that formed underwent a transition to the stable tetragonal phase (t-phase) during a suitable annealing treatment, but it was found not to undergo a phase transformation to the monoclinic phase (m-phase) in the presence of external stress. The t′-phase was confirmed to have three variants.