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

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Previous studies on copper(I) oxide (Cu2O) electron density distribution yielded controversial conclusions.
• Experimental and theoretical investigations have proposed different bonding models for Cu2O.

Purpose of the Study:

• To critically reexamine the electron-density distribution in Cu2O.
• To resolve discrepancies in earlier experimental and theoretical findings regarding Cu2O bonding.

Main Methods:

• High-quality single-crystal diffraction data collection at room temperature using 316.5 keV gamma radiation.
• Multipole refinement of the diffraction data to derive electron density.
• Extrapolation of extinction-free structure factors using multiple gamma-ray lines (200-600 keV).

Main Results:

• The derived electron density reveals a partially filled d_{z^2} orbital on copper.
• Incomplete ionization of both copper (Cu) and oxygen (O) atoms was observed.
• No interstitial charge pileup between copper atoms was detected, refuting the covalent bonding hypothesis.

Conclusions:

• The bonding in Cu2O is not primarily covalent, contrary to some earlier hypotheses.
• The electron density distribution supports an ionic model with specific orbital characteristics.
• Anharmonic contributions to thermal parameters are not supported by the data.