High-Resolution ¹⁷O NMR of Wadsleyite (β-Mg₂SiO₄)

Abstract
The sensitivity of high-resolution ¹⁷O (I = 5/2) NMR spectroscopy of solids has advanced significantly in recent years. Here we show that excellent results are now obtainable from milligram quantities of ¹⁷O-enriched materials, thereby allowing the technique to be applied to silicate phases synthesized under very high pressures in a multiple-anvil apparatus. We report the first ¹⁷O NMR study of β-Mg₂SiO₄ (9.6 mg of 35% ¹⁷O-enriched material, synthesized at p = 16 GPa and T = 1873 K), a dense phase of considerable interest in mantle geology. Using STMAS at magnetic fields of B₀ = 9.4 T and 11.7 T and MQMAS at B₀ = 18.8 T, we have resolved and assigned all four crystallographically distinct O sites and determined their chemical shift and quadrupolar parameters.