Pressure-induced phase transition in silicon nitride material |
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| Authors: | Chen Dong Yu Ben-Hai |
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| Affiliation: | College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 464000, China |
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| Abstract: | The equilibrium crystal structures, lattice parameters, elastic constants, and elastic moduli of the polymorphs α-, β-, and γ-Si3N4, have been calculated by first-principles method. β-Si3N4 is ductile in nature and has an ionic bonding. γ-Si3N4 is found to be a brittle material and has covalent chemical bonds, especially at high pressures. The phase boundary of the β → γ transition is obtained and a positive slope is found. This indicates that at higher temperatures it requires higher pressures to synthesize γ-Si3N4. On the other hand, the α → γ phase boundary can be described as P=14.37198+3.27×10-3T-7.83911×10-7T2-3.13552×1010T3. The phase transition from α- to γ-Si3N4 occurs at 16.1~GPa and 1700~K. Then, the dependencies of bulk modulus, heat capacity, and thermal expansion on the pressure P are obtained in the ranges of 0~GPa-30~GPa and 0~K-2000~K. Significant features in these properties are observed at high temperatures. It turns out that the thermal expansion of γ-Si3N4 is larger than that of α-Si3N4 over wide pressure and temperature ranges. The evolutions of the heat capacity with temperature for the Si3N4 polymorphs are close to each other, which are important for possible applications of Si3N4. |
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| Keywords: | density functional theory semiconductor heat capacity bulk modulus |
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