Predicting metallic conductivity in oxides from simple chemical criteria

The delocalization of d electrons in oxides can be described with a simple model taking into account the electronegativity and the chemical hardness. The metallic conductivity appears when (i) the electronegativity is high involving large conduction and valence bandwidths and (ii) the chemical hardness is low. From this we propose a delocalization criterion Mcrit∼η+2.8χ whereby if Mcrit is larger than 18 eV a metallic conductivity should occur. The validity of this criterion is checked in actual oxide systems. We also discuss its limits in p-elements oxides with the help of electronic band structure calculations within the density functional theory framework. We propose that this simple χη model can be used for the understanding of the electronic properties of different classes of oxides.