First-principles Study of Novel Icosahedral-Based B12CN and B13CN Structures

Boron-rich compounds with icosahedral-based structures possess rich,fascinating electronic and mechanical properties.Herein,the first comprehensive and systematic study of the crystal structures and properties of ternary B12CN and B13CN compounds with icosahedral structures has been performed by using particle swarm optimized structure pre-diction methods in combination with first-principles calcula-tions.Compared with the widely studied variant structure ofα-boron,the newly discovered Cmc21 structures are thermo-dynamically more stable for B12CN and B13CN.For structures with the same space group,B13CN possesses superior ther-modynamic stability and mechanical properties than B12CN.Electronic structure calculations indicate that the boron-rich B-C-N system has abundant and tunable electronic proper-ties,i.e.,B13CN is a semiconductor,and B12CN possesses a hole-type conducting characteristic.The systematic study of structural ideal tensile strength indicates successive damage to icosahedra and successive bond breaks between icosahedra during tensile processes,leading to interesting deformation mechanisms,such as stress re-enhancement,structural mul-tistep damage,and creep-like deformation.