Correlation between optical constants and crystal chemical parameters of ZrW 2O 8

Abstract

The refractive indices of ZrW 2O 8, measured at wavelengths of 435.8–643.8 nm, were used to calculate n D at λ=589.3 nm and n ∞ at λ=∞ from a one-term Sellmeier equation. Refractive indices, n D and dispersion values, A, are, respectively, 1.8794 and 114×10 −16 m 2. The high dispersion, relative to other molybdates, tungstates and Zr-containing compounds, is attributed to the low value of E o =7.7 eV and mean cation coordination number. Total electronic polarizabilities, α total, were calculated from n ∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 20.087 Å 3 and the calculated total polarizability α T of 17.59 Å 3 ( Δ=+12.4%) is attributed to (1) a large M–O–W angle, (2) a high degree of W 5 d–O (terminal) 2 p and Zr nd–O 2 p hybridization, and (3) unusually high oxygen displacement factors, B(O), normalized to B(W).