Structure and equation of state of tetragonal boron subnitride B50N2

Abstract

New boron subnitride B50N2 has been synthesized by crystallization from the B-BN melt at 5 GPa, and its structure has been refined using Rietveld analysis. B50N2 crystallizes in the tetragonal space group P-4n2 with unit cell parameters a = 8.8181(2) A and c = 5.0427(10) A. Quasi-hydrostatic compression of two boron subnitrides, B50N2 and B13N2, has been studied to 30 GPa at room temperature in a diamond-anvil cell using synchrotron X-ray diffraction. No pressure-induced phase transitions have been observed. A fit of experimental p-V data to the Murnaghan equation of state yielded B50N2 and B13N2 bulk moduli of 167(2) and 205(2) GPa, respectively, with fixed first bulk modulus pressure derivative of 4.0.