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Correlation between optical constants and crystal chemical parameters of ZrW2O8 |
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| Authors: | Robert D Shannon Olaf Medenbach Philippe Ghosez |
| Institution: | a Geological Sciences/CIRES, University of Colorado, Boulder, CO 80309, USA b Universität Bremen, FB 5 Geowissenschaften, Klagenfurter Straße, D-28359 Bremen, Germany c Institut für Mineralogie, Fakultät für Geowissenschaften, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum, Germany d Département de Physique, Université de Liège, B-5, B-4000 Sart Tilman, Belgium |
| Abstract: | 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). |
| Keywords: | ZrW2O8 Refractive indices Optical dispersion Electronic polarizability Born effective charges |
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