Unlike TiO2, which features six-coordinate Ti in all phases, zirconia and hafnia consist of seven-coordinate metal centres.

A variety of other crystalline phases have been experimentally observed, including cubic fluorite (Fm3m), tetragonal (P42/nmc), monoclinic (P21/c) and orthorhombic (Pbca and Pnma).

[11][12][13][14] Because of its very high melting point, hafnia is also used as a refractory material in the insulation of such devices as thermocouples, where it can operate at temperatures up to 2500 °C.

[15] Multilayered films of hafnium dioxide, silica, and other materials have been developed for use in passive cooling of buildings.

The films reflect sunlight and radiate heat at wavelengths that pass through Earth's atmosphere, and can have temperatures several degrees cooler than surrounding materials under the same conditions.