Zirconium dioxide coating on particles of titanium dioxide pigments, as a refractory material, in insulation, abrasives and enamels. Stabilized zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystal structure at high temperatures. This high ionic conductivity (and a low electronic conductivity) makes it one of the most useful electroceramics. Zirconium dioxide is also used as the solid electrolyte in electrochromic devices. Zirconia is a precursor to the electroceramic lead zirconate titanate ("PZT"), which is a high-K dielectric, which is found in myriad components. The very low
Cubic zirconia of diamond. Cubic zirconia is relatively hard, 8–8.5 on the Mohs scale— slightly harder than most semi-precious natural gems. Its refractive index is high at 2.15–2.18 (compared to 2.42 for diamonds) and its luster is adamantine. Its dispersion is very high at 0.058–0.066, exceeding that of diamond (0.044). Cubic zirconia has no cleavage and exhibits a conchoidal fracture. Because of its high hardness, it is generally considered brittle. Under shortwave UV cubic zirconia typically fluoresces a yellow, greenish yellow or "beige". Under longwave UV the effect is greatly diminished, with a whitish glow sometimes being seen. Colored stones may show