Raman spectra of phase A at various pressures and temperatures

Abstract

Variations of the Raman spectra of phase A (Mg7Si2O14H6) were investigated up to about 400 kbar at room temperature and in the range 80-853 K at atmospheric pressure. Phase A appears to undergo a reversible phase transition around 180 kbar at room temperature, and it becomes amorphous above 813 K at atmospheric pressure. The Raman frequencies of the two strong OH bands of phase A decrease linearly with increasing pressure, but increase non-linearly with increasing temperature. The frequencies of the other Raman bands of phase A increase non-linearly with increasing pressure but decrease both linearly and non-linearly with increasing temperature within the experimental uncertainties and the range investigated. The trends of the pressure and temperature effects on the Raman frequencies of phase A parallel those observed in the hydrous β-phase, but non-linear behaviour was not observed in the latter. Show more