Low temperature heat capacity measurements of β-Si3N4 and γ-Si3N4: Determination of the equilibrium phase boundary between β-Si3N4 and γ-Si3N4 |
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Affiliation: | 1. Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan;2. Collaborative Research Project of Laboratory for Materials and Structures, Tokyo Institute of Technology, Yokohama 226-8503, Japan;3. Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama 226-8503, Japan |
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Abstract: | Isobaric heat capacities of β-Si3N4 and γ-Si3N4 were measured at temperatures between 1.8 and 309.9 K with a thermal relaxation method. The measured heat capacities of γ-Si3N4 are smaller than those of β-Si3N4 in this temperature range. Using these data, we determined the standard entropies of β-Si3N4 and γ-Si3N4 to be 62.30 J·mol?1 K?1 and 51.79 J·mol?1 K?1, respectively. The equilibrium phase boundary between β-Si3N4 and γ-Si3N4 was calculated using these values and thermodynamic parameters reported in previous studies. The obtained equilibrium phase transition pressure at 2000 K is 11.4 GPa. It is lower than the experimental pressures at which γ-Si3N4 was synthesized in previous studies. The calculated Clapeyron slope at this temperature is 0.6 MPa K?1, which is consistent with those of theoretical studies. |
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Keywords: | Silicon nitride High pressure Phase boundary Heat capacity Entropy |
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