Phase Transition Characters and Thermodynamics Modeling of the Newly-Discovered wⅡ- and Post-Spinel Si3N4 Polymorphs: A First-Principles Investigation
来源期刊：Acta Metallurgica Sinica2013年第2期
论文作者：Benhai YU Dong CHEN
文章页码：131 - 136
摘 要：The equilibrium lattice constants, elastic constants and elastic moduli of wⅡ- and post-spinel Si3N4 have been investigated in the pressure ranges of 0-40 GPa and 160-240 GPa, respectively. These two phases are found to be dynamically stable. The post-spinel phase is one of the strongest materials yet investigated under extreme compressions. Some fundamental properties and phase transition characters are evaluated from the quasi-harmonic approximation. The transition pressures from the γ phase to the post-spinel phase are 152.5 GPa （at 300 K） and 181.8 GPa （at 1500 K）. The phase transition pressures of the β→ wⅡ and γ→ postspinel transitions increase with the rise of temperature; hence, at higher temperature it requires higher pressure to synthesize post-spinel Si3N4 . The heat capacity, thermal expansion and bulk modulus of the new phases are computed as functions of pressure and temperature. The heat capacity of post-spinel Si3N4 is large at high temperature and only weakly pressure dependent.
Benhai YU，Dong CHEN
College of Physics and Electronic Engineering, Xinyang Normal University
摘 要：The equilibrium lattice constants, elastic constants and elastic moduli of wⅡ- and post-spinel Si3N4 have been investigated in the pressure ranges of 0-40 GPa and 160-240 GPa, respectively. These two phases are found to be dynamically stable. The post-spinel phase is one of the strongest materials yet investigated under extreme compressions. Some fundamental properties and phase transition characters are evaluated from the quasi-harmonic approximation. The transition pressures from the γ phase to the post-spinel phase are 152.5 GPa （at 300 K） and 181.8 GPa （at 1500 K）. The phase transition pressures of the β→ wⅡ and γ→ postspinel transitions increase with the rise of temperature; hence, at higher temperature it requires higher pressure to synthesize post-spinel Si3N4 . The heat capacity, thermal expansion and bulk modulus of the new phases are computed as functions of pressure and temperature. The heat capacity of post-spinel Si3N4 is large at high temperature and only weakly pressure dependent.
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