Fianite

a synthetic crystal with no natural analogs, based on zirconium or hafnium dioxide. The name “fianite” is derived from FIAN, the Russian acronym for the Institute of Physics of the Academy of Sciences of the USSR, where the crystals were first produced. Fianites have the cubic lattice that is usually characteristic of zirconium or hafnium dioxide only at high temperatures, being unstable at room temperature. To make the lattice stable, a small amount of oxides of calcium, uranium, or other elements is added to the dioxide. In addition to the stabilizers, which constitute a few percent of the total composition, fianites may contain oxides of, for example, rare-earth or iron-group elements; these oxides greatly alter the properties of the crystals.

Fianites are obtained by crystallization from melts. Since the melting points of zirconium and hafnium dioxide are extremely high (2700° and 2800°C, respectively) and the melts are chemically aggressive, fianites cannot be obtained by conventional methods. Induction heating of the melt is used. The melted substance is placed in a closed vessel having the same chemical composition as the melt. The fianite crystals grow as the melt gradually cools. One process takes eight to ten hours and makes it possible to obtain several kilograms of crystals, each weighing up to 200–400 g. Fianites may be colorless or may be variously tinted by impurities.

Fianites have a unique set of properties, including a high melting point, a hardness of 7.5–8.5 on Mohs’ scale, a low volatility at high temperatures, a refractive index of 2.15–2.25, a density of about 6.5–10 g/cm³, and a substantial electrical conductivity at temperatures above 1200°C. They are acid-and alkali-resistant.

The variety of colors, the great hardness, and the high refractive index, which is only slightly less than the refractive index of diamonds (2.41), make fianites valuable for the jewelry industry. Fianites make it possible not only to simulate natural precious and semiprecious stones, such as sapphire, topaz, aquamarine, and garnet, but also to produce stones with unique properties.

Fianites are used in the manufacture of optical lenses and “windows” that can function at high temperatures. They are also used as laser materials and as building materials that can withstand high temperatures and chemically aggressive media.