A systematic study of OH in hydrous wadsleyite from polarized FTIR spectroscopy and single-crystal X-ray diffraction: Oxygen sites for hydrogen storage in Earth’s interior

Abstract

The incorporation of hydrogen into wadsleyite (β-Mg2SiO4) was investigated using polarized FTIR spectroscopy and X-ray diffraction on oriented single crystals. The experiments were carried out with a new suite of samples containing between ~100 and ~10 000 ppm H2O by weight (wt ppm), encompassing the H-contents most relevant to Earth's potentially hydrous mantle transition zone. Attempts to synthesize anhydrous wadsleyite resulted in water contents of no less than ~50 wt ppm H2O. An empirical relation between the b/a axial ratio against estimated wt ppm concentrations of H2O in wadsleyite (CH2O) was determined: (b/a) = 2.008(1) + 1.25(3) × 10-6 · CH2O