Abstract Two novel high-pressure structures of BeB2C2 with space groups R3m and P-4m2 are firstly reported using a swarm methodology on crystal structure search. Both two phases comprise peculiar 3D sp3 B–C bonded frameworks resulted from the strong out-of-plane twisting of the graphite-like sp2 B–C layers in ambient-pressure Pmmn structure under compression. Enthalpy difference calculations reveal that the phase transition from Pmmn to R3m structure happens at 13.7 GPa with a striking 16.4% volume drop. The R3m and P-4m2 phases are all indirect band gap semiconductor demonstrated by the electronic structure calculations. The orientation dependences of the Young's moduli and shear moduli of the these two phases were quantitatively studied. The calculated high hardness (42.7 GPa for R3m and 56.5 GPa for P-4m2) and large ideal strengths suggest that they are potential superhard materials. Analyses of atomic plastic deformations reveal that the collapse of 3D B–C frameworks in the R3m phase and the breakdown of BC4 tetrahedrons in the P-4m2 phase with the breaking of B–C bonds are responsible for their tensile-induced and shear-induced lattice instability, respectively.

中文翻译：

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二硼碳化铍的超硬高压结构

摘要 首次使用群体方法进行晶体结构搜索，报道了空间群为 R3m 和 P-4m2 的两种新型 BeB2C2 高压结构。两相都包含特殊的 3D sp3 B-C 键合框架，这是由于压缩下环境压力 Pmmn 结构中类石墨 sp2 B-C 层的强烈平面外扭曲造成的。焓差计算表明，从 Pmmn 到 R3m 结构的相变发生在 13.7 GPa 时，体积下降了 16.4%。R3m 和 P-4m2 相都是由电子结构计算证明的间接带隙半导体。定量研究了这两个相的杨氏模量和剪切模量的取向依赖性。计算出的高硬度（42.7 GPa 为 R3m 和 56. P-4m2 为 5 GPa）和较大的理想强度表明它们是潜在的超硬材料。原子塑性变形的分析表明，R3m 相中 3D B-C 框架的坍塌和 P-4m2 相中 BC4 四面体的破裂以及 B-C 键的断裂是它们的拉伸诱导和剪切诱导的原因晶格不稳定性，分别。