Heat capacity, entropy and phase equilibria of stishovite

摘要

The low-temperature heat capacity (C _P) of stishovite (SiO _2) synthesized with a multi-anvil device was measured over the range of 5-303 K using the heat capacity option of a physical properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24. 94 J mol ~(-1) K ~(-1), which is considerably smaller (by 2. 86 J mol ~(-1) K ~(-1)) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289-2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325-1330, 2011). The coesite-stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1-10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune et al. (Earth Planet Sci Lett 77:245-256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624-1629, 2007).