A new tetragonal structure type for Li2B2C

Thermodynamic stability of Li-B-C compounds from first principles

Prediction of high-T_c superconductivity in hole-doped Li_xBC two decades ago has brought about an extensive effort to synthesize new materials with honeycomb B-C layers, but the thermodynamic stability of Li-B-C compounds remains largely unexplored. In this study, we use density functional theory to characterize well-established and recently reported Li-B-C phases. Our calculation of the Li chemical potential in Li_xBC helps estimate the (T,P) conditions required for delithiation of the LiBC parent material, while examination of B-C phases helps rationalize the observation of metastable BC₃ polymorphs with honeycomb and diamond-like morphologies. At the same time, we demonstrate that recently reported BC₃, LiBC₃, and Li₂B₂C phases with new crystal structures are both dynamically and thermodynamically unstable. With a combination of evolutionary optimization and rational design, we identify considerably more natural and favorable Li₂B₂C configurations that, nevertheless, remain above the thermodynamic stability threshold.

Phase equilibria and crystal structure relationships in the ternary Li–B–C system

Phase equilibria in the Li–B–C ternary system have been investigated by X-ray powder diffraction, scanning electron microscopy, electron probe microanalysis and differential scanning calorimetry.

LiBC3: a new borocarbide based on graphene and heterographene networks

Li-B-C alloys have attracted much interest because of their potential use in lithium-ion batteries and superconducting materials. The formation of the new compound LiBC₃ [lithium boron tricarbide; own structure type, space group P-6m2, a = 2.5408 (3) Å and c = 7.5989 (9) Å] has been revealed and belongs to the graphite-like structure family. The crystal structure of LiBC₃ presents hexagonal graphene carbon networks, lithium layers and heterographene B/C networks, alternating sequentially along the c axis. According to electronic structure calculations using the tight-binding linear muffin-tin orbital-atomic spheres approximations (TB-LMTO-ASA) method, strong covalent B-C and C-C interactions are established. The coordination polyhedra for the B and C atoms are trigonal prisms and for the Li atoms are hexagonal prisms.

Li4Ge2B as a new derivative of the Mo2B5and Li5Sn2structure types

Binary and multicomponent intermetallic compounds based on lithium andp-elements of Groups III–V of the Periodic Table are useful as modern electrode materials in lithium-ion batteries. However, the interactions between the components in the Li–Ge–B ternary system have not been reported. The structure of tetralithium digermanium boride, Li4Ge2B, exhibits a new structure type, in the noncentrosymmetric space groupR3m, in which all the Li, Ge and B atoms occupy sites with 3msymmetry. The title structure is closely related to the Mo2B5and Li5Sn2structure types, which crystallize in the centrosymmetric space groupR\overline{3}m. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight-binding–linear muffin-tin orbital–atomic spheres approximation (TB–LMTO–ASA) method, strong covalent Ge—Ge and Ge—B interactions were established.