Temperature and wavelength dependence of refractive index of zircon and hafnon

Abstract We report for the first time measurement of refractive indices of zircon and hafnon as a function of temperature and wavelength. Single crystals of both materials were grown by slow cooling in a sodium molybdate flux. The thermal birefringence coefficients of zircon and hafnon were determined to be −61 × 10−6 and −197 × 10−6 K−1 at 1549 nm, respectively, with an uncertainty of ±50 × 10−6 K−1. Alloying of zircons with opposite thermal birefringences to produce a material with a large birefringence that is insensitive to temperature (athermalization) is discussed. Solubility in the zircon-xenotime system was evaluated experimentally and by computer modeling. Despite the small (0.5–4%) difference in lattice parameters, the zircon-xenotime system exhibits a wide miscibility gap.