Ceria-zirconia oxides is thermodynamically favorable in a wide range of solid solution compositions, which means that ceria-zirconia is metastable with respect to phase separation. Ceria-zirconia is widely used as a component in current three-way catalytic converters. The ceria-based component of the converter has several functions, including promoting the dispersion of the noble metals in the catalyst, but also storing and releasing oxygen. The incorporation of zirconium in modern converters, forming ceria-zirconia, improves the performance of the catalyst by enhancing the resistance of the material to sintering, and simultaneously increasing the ability of the oxide to accommodate oxygen vacancies in its structure.
Zirconium dioxide coatings; it is a high-index material usable from the near-UV to the mid-IR, due to its low absorption in this spectral region. In such applications, it is typically deposited by PVD. In jewelry making, some watch cases are advertised as being "black zirconium oxide". In 2015 Omega released a fully ZrO watch named "The Dark Side of The Moon" with ceramic case, bezel, pushers and clasp, advertising it as four times harder than stainless steel and therefore much more resistant to scratches during everyday use. Single crystals of the cubic phase of zirconia are commonly used as diamond simulant in