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

Abstract The low-temperature isobaric heat capacity (CP) of synthetic stishovite was measured between 2 and 311 K by the thermal relaxation method. The measured CP is considerably smaller than that of Holm et al. (1967) over the whole temperature range studied. The standard entropy, So298.15, 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 CP, 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 So298.15 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).