Pressure-tuned correlation field splitting in phase A (Mg₇Si₂O₈(OH)₆)

抄録

A previous high-pressure Raman spectroscopic study of phase A (Mg₇Si₂O₈(OH)₆) by Liu et al. (1997) showed that two O-H stretching bands gradually approach each other up to 18 GPa, but do not intersect and move apart thereafter. In this study, vibrational calculations of phase A were performed to elucidate the origin of this behavior. The calculations with and without deuterium substitution show that pressure-tuned correlation field splitting of O-H stretching vibration is responsible for this curious behavior. The observed pressure changes in the O-H stretching frequencies were qualitatively reproduced. In phase C (=superhydrous phase B), the two O-H bands observed about 60 cm^-1 apart at 1 atm were found to be the result of correlated field splitting. The effect of correlation field splitting on the O-H stretching vibration modes is easily overlooked but can be clarified by vibrational calculations that mimic the isotope dilution method, as demonstrated in this study.