Optical constants and crystal chemical parameters of Sc2W3O12

The refractive indices of Sc2W3O12, measured at wavelengths of 435.8–643.8 nm, were used to calculate na = 1.7331, nb = 1.7510, nc = 1.7586 at λ = 589.3 nm and n∞ values at λ = ∞ from a one-term Sellmeier equation. Mean refractive indices, 〈nD〉, and mean dispersion values, 〈A〉, are, respectively, 1.7475 and 110 × 10−16 m2. Total electronic polarizabilities, αobs, were calculated from n∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 28.415 Å3 and the calculated total polarizability αT of 26.74 Å3 (Δ = +6.3%) is attributed to (1) a large M–O–W angle, and (2) a high degree of W 5d–O 2p and Sc nd–O 2p hybridization, where n signifies unspecified Sc d orbitals.