Via structural searching methodology and first-principles calculations, we predicted two new BC6N allotropes, a Ccentered monoclinic BC6N（Cm-BC6N） and a primitive-centered monoclinic BC6N（Pm-BC6N）.The lattice vibr...Via structural searching methodology and first-principles calculations, we predicted two new BC6N allotropes, a Ccentered monoclinic BC6N（Cm-BC6N） and a primitive-centered monoclinic BC6N（Pm-BC6N）.The lattice vibrations,elastic properties, ideal strength, theoretical hardness, and electronic structure of the predicted BC6N were investigated systematically.Our results reveal that Cm-BC6N is more favorable energetically than graphite-like g-BC6N above 20.6 GPa,which is lower than the transition pressures of r-BC6N, t-BC6N, and Pm-BC6N.Both Cm-BC6N and Pm-BC6N are indirect semiconductors with band gaps of 2.66 eV and 0.36 eV, respectively.Cm-BC6N exhibits the excellent ideal shear strength of 53.9 GPa in（011）■, much greater than that of Pm-BC6N（25.0 GPa in（010）[101] shear direction）, and Cm-BC6N shows a much lower anisotropy in shear strength than Pm-BC6N.The Vickers hardness of Cm-BC6N is estimated to be above 80 GPa, which is more outstanding than those of t-BC6N and r-BC6N.展开更多
A potential superhard o-BC_4 N with Imm2 space group is identified by ab initio evolutionary methodology using CALYPSO code. The structural, electronic and mechanical properties of o-BC_4N are investigated. The elasti...A potential superhard o-BC_4 N with Imm2 space group is identified by ab initio evolutionary methodology using CALYPSO code. The structural, electronic and mechanical properties of o-BC_4N are investigated. The elastic calculations indicate that o-BC_4N is mechanically stable. The phonon dispersions imply that this phase is dynamically stable under ambient conditions. The structure of o-BC_4N is more energetically favorable than o-BC_4N above the pressure of 25.1 GPa. Here o-BC_4N is a semiconductor with an indirect band gap of about 3.95 eV, and the structure is highly incompressible with a bulk modulus of 396.3 GPa and shear modulus of 456.0 GPa. The mechanical failure mode of o-BC_4N is dominated by the shear type. The calculated peak stress of 58.5 GPa in the(100)[001] shear direction sets an upper bound for its ideal strength. The Vickers hardness of o-BC_4N reaches 78.7 GPa, which is greater than that of t-BC_4N and bc-BC_4N proposed recently, confirming that o-BC_4N is a potential superhard material.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21671168 and 21875205)the Hebei Natural Science Foundation,China(Grant No.B2015203096)the Qinhuangdao Science and Technology Support Program,China(Grant No.201703A014)
文摘Via structural searching methodology and first-principles calculations, we predicted two new BC6N allotropes, a Ccentered monoclinic BC6N（Cm-BC6N） and a primitive-centered monoclinic BC6N（Pm-BC6N）.The lattice vibrations,elastic properties, ideal strength, theoretical hardness, and electronic structure of the predicted BC6N were investigated systematically.Our results reveal that Cm-BC6N is more favorable energetically than graphite-like g-BC6N above 20.6 GPa,which is lower than the transition pressures of r-BC6N, t-BC6N, and Pm-BC6N.Both Cm-BC6N and Pm-BC6N are indirect semiconductors with band gaps of 2.66 eV and 0.36 eV, respectively.Cm-BC6N exhibits the excellent ideal shear strength of 53.9 GPa in（011）■, much greater than that of Pm-BC6N（25.0 GPa in（010）[101] shear direction）, and Cm-BC6N shows a much lower anisotropy in shear strength than Pm-BC6N.The Vickers hardness of Cm-BC6N is estimated to be above 80 GPa, which is more outstanding than those of t-BC6N and r-BC6N.
基金Supported by the National Natural Science Foundation of China under Grant Nos 21671168 and 21875205the Hebei Natural Science Foundation under Grant No B2015203096the Qinhuangdao Science and Technology Support Program under Grant No 201703A014
文摘A potential superhard o-BC_4 N with Imm2 space group is identified by ab initio evolutionary methodology using CALYPSO code. The structural, electronic and mechanical properties of o-BC_4N are investigated. The elastic calculations indicate that o-BC_4N is mechanically stable. The phonon dispersions imply that this phase is dynamically stable under ambient conditions. The structure of o-BC_4N is more energetically favorable than o-BC_4N above the pressure of 25.1 GPa. Here o-BC_4N is a semiconductor with an indirect band gap of about 3.95 eV, and the structure is highly incompressible with a bulk modulus of 396.3 GPa and shear modulus of 456.0 GPa. The mechanical failure mode of o-BC_4N is dominated by the shear type. The calculated peak stress of 58.5 GPa in the(100)[001] shear direction sets an upper bound for its ideal strength. The Vickers hardness of o-BC_4N reaches 78.7 GPa, which is greater than that of t-BC_4N and bc-BC_4N proposed recently, confirming that o-BC_4N is a potential superhard material.
