Thermodynamic properties of stishovite by low-temperature heat capacity measurements and the coesite-stishovite transition boundary

The low-temperature isobaric heat capacity (C P ) of synthetic stishovite was measured between 2 and 311 K by the thermal relaxation method. The measured C P is considerably smaller than that of Holm et al. (1967) over the whole temperature range studied. The standard entropy, S o 298.15 , of stishovite obtained is 24.0 J/(mol∙K), which is 3.8 J/(mol∙K) lower than that of Holm et al. (1967). Using the measured C P , the Debye temperature and thermal Grüneisen parameter at 298.15 K were calculated to be 1109 K and 1.68, respectively. The equilibrium coesite-stishovite transition boundary was calculated using the S o 298.15 of stishovite from published thermodynamic data. The calculated boundary has a slope of 3.2 ± 0.1 MPa/K at 1200-1600 K, which is larger than the slope determined by the high-pressure in situ X-ray diffraction study by Zhang et al. (1996).