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

The structure of a single crystal hydrous ringwoodite, Mg1.89Si0.98H0.30O4 synthesized at conditions of 1300 °C and 20 GPa has been analyzed. Crystallographic data for hydrous ringwoodite obtained are; Cubic with Space group: Fd3m (no. 227). a= 8.0693(5) A, V=526.41(9) A3, Z=8, Dcalc= 3.48 g cm−3. The results of site occupancy refinement using higher angle reflections showed the existence of a small degree of Mg2+-Si4+ disorder in the structure such as (Mg1.84Si0.05□0.11)(Si0.93Mg0.05□0.02)H0.30O4. The IR and Raman spectra were measured and OH vibration spectra were observed. A broad absorption band was observed in the 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 suggest that locations between O-O pairs around the octahedral 16c and 16d sites are possible sites for hydrogen.