- published: 17 Aug 2015
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Zirconium dioxide (ZrO2), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral baddeleyite. The high temperature cubic crystalline form is rarely found in nature as mineral tazheranite (Zr,Ti,Ca)O2 (and a doubtful mineral arkelite). This form, also called cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.
Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2 has a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at increasing temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces very large stresses, and will cause pure ZrO2 to crack upon cooling from high temperatures. Several different oxides are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium(III) oxide (Ce2O3), amongst others.