Electronic structure and mechanical properties of layered compound YB2C2: A promising precursor for making two dimensional (2D) B2C2 nets

Layered compounds play pivotal roles as precursors for producing 2D materials through mechanical exfoliation (micro-mechanical cleavage) or chemical approaches. Therefore, searching for layered compounds with sharp anisotropic chemical bonding and properties becomes emergent. In this work, the stability, electronic structure, elastic properties, and lattice dynamics of YB2C2 were investigated. Strong anisotropy in elastic properties is revealed, i.e., high Young's modulus in a-b plane but low Young's modulus in c direction. The maximum to minimum Young's modulus ratio is 2.41 and 2.45 for YB2C2 with P42/mmc and P4/mbm symmetry, respectively. The most likely systems for shear sliding or micro-delaminating are (001)[100] and (001)[010]. The anisotropic elastic properties are underpinned by the anisotropic chemical bonding, i.e., strong bonding within the B2C2 nets and weak bonding between Y atom layers and B2C2 nets. YB2C2 is electrically conductive and the contributions to the electrical conductivity are from delocalized Y 4deg as well as B 2pz and C 2pz electrons. The layered crystal structure, sharp anisotropic mechanical properties, and metallic conductivity endorse YB2C2 promising as a precursor for new 2D B2C2 nets.