Synthesis of Hexagonal CaB3C3 with a Zeolite-Type Framework
Timothy A. Strobel, Piotr A. Guńka, Tiange Bi, Wencheng Lu, Mads F. Hansen, Michael J. Hutcheon, Samuel G. Dunning, Li Zhu, Davide M. Proserpio, Stella Chariton, Vitali B. PrakapenkaAbstract
We report the synthesis of a calcium-intercalated boron–carbon framework with the “NPO” zeolite topology. Hexagonal CaB3C3 crystallizes in space group P62m (No. 189), under high-pressure, high-temperature conditions, in a structure predicted for hypothetical metastable carbon allotropes. The structure, which exhibits minimal or no substitutional framework disorder, is comprised of four-coordinated B/C atoms that form channels along the crystallographic Z-axis, trapping calcium ions. Calculations based on density functional theory (DFT) indicate that hexagonal CaB3C3 is thermodynamically stable above 30 GPa, and theoretical/experimental results suggest that the recoverable compound exhibits a superconducting transition near 5 K at ambient pressure. The formation of hexagonal CaB3C3 further expands the range of synthesizable structural topologies for carbon-based tetrahedral nets with versatile physical properties.