Fluid synthesis and structure of a new boron nitride polymorph—hyperdiamond fulborenite B₁₂N₁₂ (E phase)

Abstract

A new boron nitride polymorph is prepared for the first time by supercritical fluid synthesis in a high-pressure gazostat at a pressure P < 200 MPa and a temperature T < 1000°C in various atmospheres. The formation of the new phase is confirmed by x-ray diffraction and infrared absorption spectroscopy. A number of lines in the x-ray diffraction patterns and infrared absorption spectra of the new phase coincide with those described in the literature for the so-called E phase. On this basis, the conclusion is drawn that the E phase of boron nitride is most likely formed during supercritical fluid synthesis. Since the structure of the E phase is as yet unknown, a model structure of the new phase is proposed in the form of a diamond-like lattice with the sites occupied by molecules of the fulborene B₁₂N₁₂. The proposed structure is confirmed by the good agreement between the calculated and experimental values of the lattice parameters (A = 1.152 and 1.114 nm, respectively), densities (ρ = 2.59 and 2.50–2.60 g/cm³, respectively), and x-ray diffraction patterns. This new boron nitride zeolite with a faujasite lattice is given the name hyperdiamond fulborenite B₁₂N₁₂. The calculated bulk modulus of the hyperdiamond fulborenite B = 658 GPa is higher than that of diamond.