Three-Dimensional Metallic Boron Carbide: Stability and Properties.

The design of novel materials through the strategic modification of their structural building blocks represents a powerful approach to achieving significant advancements in materials science. This study thoroughly examines the structural, mechanical, electronic, acoustic, and thermodynamic properties of a three-dimensional monoclinic boron carbide (3D m-BC) structure using first-principles methods based on density functional theory (DFT). We introduce a unique cage-based 3D monoclinic boron carbide structure, constructed from 4-, 5-, and 6-membered rings, which demonstrates remarkable dynamic, thermal, and mechanical stability. Our advanced first-principles calculations reveal that this architecture exhibits metallic characteristics, as confirmed by both GGA-PBE and HSE06 hybrid functionals. In contrast to the ductile and low Vickers hardness 3D-BC, the 3D m-BC displays significant brittleness, a high Vickers hardness of 45.40 GPa (32.36 GPa), a low Poisson's ratio of 0.188, and a universal anisotropic index of 0.903. When compared to established thermal coating (TBC) materials such as yttria-stabilized zirconia (YSZ), which has a fracture toughness range of 2.0 to 2.3 MPa m and a minimum thermal conductivity of 2.20 W m K, the 3D m-BC demonstrates superior fracture toughness of 5.336 MPa m and a minimum thermal conductivity of 3.773 W m K. These exceptional characteristics suggest that 3D m-BC could serve as a compelling candidate for applications in environmental protection, thermal barriers, and oxygen-resistant coatings. The material exhibits a Debye temperature of 1524.15 K, an acoustic Grüneisen constant of 1.240, and a phonon thermal conductivity of 85.52 W m K at 300 K. Its melting temperature is 3311.94 K, with a thermal expansion coefficient of 7.337 μK and notable phonon inelastic scattering. These findings expand the range of boron carbide materials with new properties, presenting exciting prospects for advanced engineering applications and encouraging further experimental synthesis efforts.