Compton-profile anisotropies in graphite and hexagonal boron nitride

Abstract

The Compton profiles of pyrolytic graphite and pyrolytic boron nitride have been measured in the directions of the $c$ axis (${J}_{\ensuremath{\parallel}}$) and perpendicular to it (${J}_{\ensuremath{\perp}}$), using 60-keV $\ensuremath{\gamma}$ rays of $^{241}\mathrm{Am}$. The anisotropy measured in boron nitride is found to be significantly smaller than that in graphite near zero momentum. This is consistent with the different character of the $\ensuremath{\pi}$ electrons in the two materials. We find ${J}_{\ensuremath{\parallel}}\ensuremath{-}{J}_{\ensuremath{\perp}}$ to be negative near zero momentum for both graphite and boron nitride, the same as in all previously known measurements of graphite. To our knowledge, no other Compton anisotropy measurements of hexagonal boron nitride have been reported. Our results disagree with recently published linear combination of atomic orbitals self-consistent-field calculations, where ${J}_{\ensuremath{\parallel}}\ensuremath{-}{J}_{\ensuremath{\perp}}$ was found to be positive near zero momentum for both materials.