Abstract
The structural, mechanical, anisotropic, electronic, and thermal properties of t-Si3N4, t-Si2GeN4, t-SiGe2N4, and t-Ge3N4 in the tetragonal phase are systematically investigated in the present work. The mechanical stability is proved by the elastic constants of t-Si3N4, t-Si2GeN4, t-SiGe2N4, and t-Ge3N4. Moreover, they all demonstrate brittleness, because B/G < 1.75, and v < 0.26. The elastic anisotropy of t-Si3N4, t-Si2GeN4, t-SiGe2N4, and t-Ge3N4 is characterized by Poisson’s ratio, Young’s modulus, the percentage of elastic anisotropy for bulk modulus AB, the percentage of elastic anisotropy for shear modulus AG, and the universal anisotropic index AU. The electronic structures of t-Si3N4, t-Si2GeN4, t-SiGe2N4, and t-Ge3N4 are all wide band gap semiconductor materials, with band gaps of 4.26 eV, 3.94 eV, 3.83 eV, and 3.25 eV, respectively, when using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. Moreover, t-Ge3N4 is a quasi-direct gap semiconductor material. The thermodynamic properties of t-Si3N4, t-Si2GeN4, t-SiGe2N4, and t-Ge3N4 are investigated utilizing the quasi-harmonic Debye model. The effects of temperature and pressure on the thermal expansion coefficient, heat capacity, Debye temperature, and Grüneisen parameters are discussed in detail.
Highlights
IV A Group nitrides have attracted considerable interest as high-performance ceramics due to their outstanding physical properties [1]
Fan et al [38] investigated the elastic anisotropic and electronic properties of m-Si3 N4, o-Si3 N4, and t-Si3 N4 under high pressure. They found that the m-Si3 N4 transition from the direct band gap to the indirect band gap state occurred at ~32 GPa
We investigate and discuss the structural, elastic, electronic, and thermodynamic properties for t-Six Ge3−x N4 (x = 0, 1, 2, 3) alloys, which would be helpful for future experiments and theoretical explorations
Summary
IV A Group nitrides have attracted considerable interest as high-performance ceramics due to their outstanding physical properties [1]. Fan et al [38] investigated the elastic anisotropic and electronic properties of m-Si3 N4 , o-Si3 N4 , and t-Si3 N4 under high pressure They found that the m-Si3 N4 transition from the direct band gap to the indirect band gap state occurred at ~32 GPa. Most of the Si3 N4 and Ge3 N4 semiconductors are wide band gap semiconductors; most of them are indirect band gap semiconductors, such as α-Si3 N4 , β-Si3 N4 , o-Si3 N4 , t-Si3 N4 , post-spinel Si3 N4 , and α-Ge3 N4 [7,36,40,41]. Ma et al [45] studied the structural, mechanical, elastic, anisotropic, and electronic properties of the monoclinic phase of m-Six Ge3−x N4 (x = 0, 1, 2, 3) alloys.
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