Structure and cation disorder of hydrous ringwoodite, gamma-Mg1.89Si0.98H0.30O4

The structure of a single crystal hydrous ring-woodite. Mg1.89Si0.98H0.30O4 synthesized at conditions of 1300 degrees C and 20 GPa has been analyzed. Crystallographic data for hydrous ringwoodite obtained are; Cubic with Spac e group: Fd3m (no. 227). a = 8.0693(5) Angstrom, V = 526.41(9) Angstrom(3), Z = 8, 3.48 g cm(-3). The results of site occupancy refinement using highe r angle reflections showed the existence of a small degree of Mg2+-Si4+ dis order in the structure such as (Mg(1.84)Si(0.05)rectangle(0.11))(Si(0.93)Mg (0.05)rectangle(0.02))H0.30O4 The IR and Raman spectra were measured and OH vibration spectra were observed. A broad absorption band was observed in t he IR spectrum and the maxima were observed at 3160 cm(-1) in the IR and at 3165 cm(-1) and 3685 cm(-1) in relatively sharp Raman spectra, which sugge st that locations between O-O pairs around the octahedral 16c and 16d sites are possible sires for hydrogen.