Correlation between optical constants and crystal chemical parameters of ZrW2O8

The refractive indices of ZrW2O8, measured at wavelengths of 435.8–643.8 nm, were used to calculate nD at λ=589.3 nm and n∞ at λ=∞ from a one-term Sellmeier equation. Refractive indices, nD and dispersion values, A, are, respectively, 1.8794 and 114×10−16 m2. The high dispersion, relative to other molybdates, tungstates and Zr-containing compounds, is attributed to the low value of Eo=7.7 eV and mean cation coordination number. Total electronic polarizabilities, αtotal, were calculated from n∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 20.087 Å3 and the calculated total polarizability αT of 17.59 Å3 (Δ=+12.4%) is attributed to (1) a large M–O–W angle, (2) a high degree of W 5d–O(terminal) 2p and Zr nd–O 2p hybridization, and (3) unusually high oxygen displacement factors, B(O), normalized to B(W).