Ab Initio Study Of Double Oxides ZnX ₂ O ₄ (X=Al, Ga, In) Having Spinel Structure

Electronic structure and optical spectra of ZnX 2 O 4 (X=Al, Ga, and In) have been studied by density functional calculations. It is shown that ZnX 2 O 4 posses a large fundamental band gap and a second gap defined as the energy difference between the two lowest conduction band (CB) energies. The second gap is found to be ∼2 eV for ZnAl 2 O 4 and >2.8 for ZnGa 2 O 4 and ZnIn 2 O 4 . The bottommost CB for ZnX 2 O 4 is well dispersive, which means that these materials possess the feature to conduct electrical current by CB electrons. Effective masses of electrons and holes are of the same order as those of the well‐known ZnO and In 2 O 3 . Optimized equilibrium structural parameters and bulk modulus for ZnAl 2 O 4 and ZnGa 2 O 4 are found to be in good agreement with the available experimental values and these values for ZnIn 2 O 4 are predicted. Chemical bonding is found to be mixed ionic–covalent with predominant ionic character.