Reassessment of the electron density in Cu₂O using γ-ray diffraction

The electron-density distribution in Cu₂O has been critically reexamined to test controversial conclusions from earlier experimental and theoretical studies. The electron density is derived via multipole refinement of high-quality single-crystal diffraction data, collected at room temperature with 316.5 keV gamma radiation. Four γ-lines in the energy range 200–600 keV have been used to extrapolate extinction-free low-order structure factors. The remaining extinction corrections refine to a crystal mosaicity identical to the observed one. There is no support for anharmonic contributions to the thermal parameters. Important features of the derived electron density are (i) a partially filled orbital, (ii) an incomplete ionization of Cu and O, and (iii) no interstitial Cu–Cu charge pileup, thereby refuting the covalent bonding hypothesis.