Empirically, intrinsic defects in SnO2 are known to give rise to a net oxygen substoichiometry and n-type conductivity; however, the atomistic nature of the defects is unclear. Through first-principles density functional theory calculations, we present detailed analysis of both the formation energies and electronic properties of the most probable isolated defects and their clustered pairs. While stoichiometric Frenkel and Schottky defects are found to have a high energetic cost, oxygen vacancies, compensated through Sn reduction, are predicted to be the most abundant intrinsic defect under oxygen-poor conditions. These are likely to lead to conductivity through the mobility of electrons from Sn(II) to Sn(IV) sites. The formation of Sn interstitials is found to be higher in energy, under all charge states and chemical environments. Although oxygen interstitials have low formation energies under extreme oxygen-rich conditions, they relax to form peroxide ions (O2 2−) with no possible mechanism for p-type conductivity.

The Cu I -based delafossite structure, Cu I M III O 2 , can accommodate a wide range of rare earth and transition metal cations on the M III site. Substitutional doping of divalent ions for these trivalent metals is known to produce higher p-type conductivity than that occurring in the undoped materials. However, an explanation of the conductivity anomalies observed in these p-type materials, as the trivalent metal is varied, is still lacking. In this article, we examine the electronic structure of Cu I M III O 2 ͑M III =Al,Cr,Sc,Y͒ using density functional theory corrected for on-site Coulomb interactions in strongly correlated systems ͑GGA+ U͒ and discuss the unusual experimental trends. The importance of covalent interactions between the M III cation and oxygen for improving conductivity in the delafossite structure is highlighted, with the covalency trends found to perfectly match the conductivity trends. We also show that calculating the natural band offsets and the effective masses of the valence band maxima is not an ideal method to classify the conduction properties of these ternary materials.

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The geometry and electronic structure of copper-based p-type delafossite transparent conducting oxides, CuMO 2 (M = In, Ga, Sc), are studied using the generalized gradient approximation (GGA) corrected for on-site Coulomb interactions (GGA + U ). The bonding and valence band compositions of these materials are investigated, and the origins of changes in the valence band features between group 3 and group 13 cations are discussed. Analysis of the effective masses at the valence and conduction band edge explains the experimentally reported conductivity trends.

The widths of the valence bands in the copper ͑I͒ delafossites CuGaO 2 , CuInO 2 , and CuScO 2 have been measured by O K-shell x-ray emission spectroscopy and are compared with previous experimental work on CuAlO 2 and CuCrO 2. In agreement with recent density-functional theory calculations it is found that the bandwidth decreases in the series CuAlO 2 Ͼ CuGaO 2 Ͼ CuInO 2 Ͼ CuScO 2. It is shown that states at the top of the valence band are of dominant Cu 3d z 2 atomic character but with significant mixing with O 2p states.