Theoretical Study Of The Ternary Spinel Nitride System Si3n4-Ge3n4
PHYSICAL REVIEW B(2003)
摘要
Total-energy density-functional theory is combined with statistical pseudobinary alloy theory to investigate the thermodynamic stability within the ternary spinel nitride system Si3N4-Ge3N4. The spinel structure has two cation sites; one of octahedral symmetry and the other of tetrahedral symmetry. The energetics show that Si favors the octahedral sites, while Ge favors the tetrahedral sites. Statistical calculations show that Si3N4-Ge3N4 forms solid solution/alloys of (SixGe1-x)(3)N-4 at high temperatures, but miscibility gaps in alloy composition appear at lower temperature. The calculated stable/metastable boundary lines at ambient pressure are discussed. The GeSi2N4 ternary "normal" spinel is predicted to be stable and we propose it as a target for synthesis at high pressure. This predicted ternary nitride theoretically is a direct wide-band-gap semiconductor and its Vickers hardness is near 28 GPa. The prediction of a stable ternary normal spinel GeSi2N4 and the thermal stability/decomposition of solid solutions of (SixGe1-x)(3)N-4 is compared with previous theoretical studies and available experimental data.
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关键词
thermodynamic stability,band structure,shock wave,system,electron density,band gap,high pressure,phase separation,solid solution,thermal stability
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