Electronic Structures And Optical Properties Of BC₃ Under High Pressure

The group of materials with BCN composition has longbeen of interest. Diamond, cubic boron nitride, and the newlyemerged C3N4 and BC2N have all been investigated as superhardmaterials. Graphite-like BC3, a member of the group, wassynthesized in laboratory in 1986. It is known that diamond, thehardest in nature, is a high pressure phase of graphite, whicharouses our study on the high pressure behavior of BC3. In this work, we carried out a first principles calculation onthe properties of BC3 under high pressures in the framework ofLocal Density Approximation (LDA) based on the densityfunctional theory. The phenomena found are as follows: (1) at20GPa, the material undergoes an electronic transition from asemiconductor to a metal;(2) at 35GPa, a structural phasetransformation occurs and the layered BC3 changes into a networkconfiguration. Further optimization of the high pressure networkunder zero pressure discloses its metastability. The high bulkmodulus 360 for BC3, suggesting its possible superhardness.Optical properties identify the intrinsic frequency of the BC3using the Lorentz model. At 0GPa, they are 2.4eV, 3.6eV, 5.7eV and12.5eV;at 40GPa, they are 1.1eV, 3.8eV and 12.1eV. The plasmafrequencies of them are 27.2eV and 28.8eV, respectively. The lowfrequency absorption spectrum of the network structure is differentfrom that of the layered structure, which can be used to identify thephase transition from the spectrum in the experiments.