Zirconia, ZrO 2 , is one of the most studied metal oxide ceramics with several interesting properties in both pure and doped forms, which includes high hardness, ionic conductivity and low thermal conductivity. Thus, it finds application both as a hard ceramic , as an electrolyte in solid oxide fuel cells , and for thermal barrier coatings . In its pure form, zirconia is observed to have three stable phases at ambient pressure depending on the temperature. At low temperature, the structure is monoclinic, at intermediate temperatures a tetragonal polymorph is stable, and at high temperatures the cubic fluorite structure is stable . The tetragonal and cubic polymorphs are shown in Fig. , and the monoclinic polymorph in Fig. .