Pressure-induced phase transition and electronic properties of MgB2C2

Two thermodynamically stable new high-pressure phases of MgB2C2 with P-3m1 and I4 cm structure were uncovered through first principles crystal structure search based on unbiased evolutionary simulations. Compared with oC80-MgB2C2 and oP10-MgB2C2 phases, the theoretically predicted hP5-MgB2C2 and tI20-MgB2C2 phases show an intriguing three-dimensional (3D) sp(3) B-C bonded network, instead of original 2D sp(2) B-C layers, which has been confirmed with the analysis of their structures and partial densities of states. The phase transitions of oC80-MgB2C2 -> oP10-MgB2C2, oP10-MgB2C2 -> hP5-MgB2C2, and hP5-MgB2C2 -> tI20-MgB2C2 occur at 4.6 GPa, 18.9 GPa, and 247.5 GPa, respectively, which have been determined according to the examination of enthalpy differences curves. Electronic band structure calculations suggest that the oC80-MgB2C2, oP10-MgB2C2 and hP5-MgB2C2 phases are indirect band gap semiconductor, while the tI20-MgB2C2 phase changes to direct band gap semiconductor. Published by AIP Publishing.