Cage-Based 3D Tetrahexagonal Boron Nitride Crystal with Excellent Terahertz Light Absorption

In recent findings, a new classification of 1D and 2D tetrahexagonal boron nitrides (th-BN) consisting of square and hexagonal rings has been documented. These materials exhibit impressive properties such as the tunable band gap, strong optical absorption, suitable sign-tunable Poisson's ratio, and high ideal strength, making them promising for applications in nano- and opto-electronic industries. Stimulated by these studies, we have designed a cage-based three-dimensional tetrahexagonal boron nitride (3D th-B₆N₆) structure, which demonstrates excellent thermal, dynamic, and mechanical stability, including exceptional cohesive and formation energies of 6.66 and -0.93 eV per atom. Unlike direct band gap 1D and 2D tetrahexagonal boron nitride semiconductors, the proposed 3D tetrahexagonal boron nitride exhibits an insulating nature, with a wide indirect band gap of 6.175 eV at the HSE06 level. Moreover, in contrast to the unequal chemical bonding and ultraviolet optical absorption observed in the 2D th-BN sheet, all B and N atoms form a fully sp³-hybridized bonded 3D th-B₆N₆ structure, with excellent terahertz light absorption in the range of 0.3-10 THz. Notably, it also exhibits a Debye temperature of 1304.55 K and substantial phonon inelastic scattering. Our study introduces the BN family with novel properties and potential applications.