Color and Conductivity in Cu₂O and CuAlO₂: A Theoretical Analysis of d¹⁰···d¹⁰ Interactions in Solid-State Compounds

The influence of homoatomic d 10 ···d 10 interactions in the structural and physical properties of some copper-containing oxides has been investigated by using semiempirical band structure calculations of the extended Hückel type. Comparison of the band structures of CuAlO 2 and Cu 2 O, two compounds with Cu(I) ions in practically identical coordination environments, reveals that the spatial arrangement of Cu···Cu contacts is responsible for their markedly different electrical and optical properties. The three-dimensional net of short Cu···Cu distances present in Cu 2 O is found to be essential for the appearance of color in this p-type semiconductor. In doped CuAlO 2, on the contrary, the 2-D nature of the array of Cu···Cu contacts leads to optical transparency and a lower conductivity if compared to cuprite.