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 Huckel type. Comparison of the band structures of CuAlO2 and Cu2O, 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 Cu2O is found to be essential for the appearance of color in this p-type semiconductor. In doped CuAlO2, 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.