Article ID Journal Published Year Pages File Type
10714008 Physica B: Condensed Matter 2012 5 Pages PDF
Abstract
Since the discovery of post-spinel Si3N4, its fundamental physical properties are highly required. In this paper, theoretical calculations are performed to investigate the structural and elastic properties of the β-, γ-, wII- and post-spinel Si3N4 polymorphs. The calculated ground-state properties compare well with available experiments. The phase transformations of the β-, γ-, wII- and post-spinel phases are investigated by the famous plane-wave pseudo-potential density functional theory. From the elastic constants obtained, we find that β-, γ- and wII-Si3N4 are stable at 0 GPa and the post-spinel phase is unstable/stable at 0 GPa/160 GPa. When the high-temperature β→γ transformation is bypassed due to kinetic reasons, β-Si3N4 is predicted to undergo a first-order phase transition to a new phase (wII-Si3N4). It is found that the transition pressures of β→wII and γ→post-spinel transitions are 20.8 GPa and 152.5 GPa, respectively. The phase boundary of the γ→post-spinel transition can be described as P=152.3631−6.39×10−3T+2.01062×10−5T2−1.93962×10−9T3. Through the quasi-harmonic approximation, the dependences of heat capacity, entropy, thermal expansion coefficient and the Debye temperature on temperature, are also successfully predicted.
Related Topics
Physical Sciences and Engineering Physics and Astronomy Condensed Matter Physics
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