Electron distribution in BN

Abstract

The Compton profiles of cubic and hexagonal BN have been measured with AgKα X-rays on polycrystalline samples and reveal a somewhat broader distribution in electron momenta for the cubic form. The structure factors for cubic BN were measured on a polycrystalline sample with monochromatic MoKα and CuKα. The values of the 111 and 200 structure factors (the latter is absent in diamond) reveal a significant change in the valence electron distribution as compared to a superposition of free-atom charge densities. Solid state theoretical structure factors are available for comparison in the following paper (Euwema, Surratt, Wilhite and Wepfer 1974). The Debye-Waller factor for cubic BN indicates an effective Debye temperature only about one half that of diamond (750°K compared to 1500°K) but this is consistent with specific heat measurements for diamond and cubic BN. The magnitude of the (420) structure factor suggests that the thermal mean-square displacement of the boron atoms is larger than that of the nitrogen atoms.