First-principles calculations of structural, electronic and optical properties of ZnGa_xAl_(2-x)O_4 spinel-type oxides

摘要

The structural, electronic and optical properties of the perfect ZnGa_xAl_(2-x)O_4 oxides have been computed by density functional theory. It is found that Al substituted by Ga gives rise to the formation of the pseudo-cubic spinel-type structure. With the increase of Ga concentration, average bond lengths of O-Al and O-Ga are greater than that of Al_2O_3 and Ga_2O_3, respectively. The zinc aluminate has direct band structure of 3.895 eV while the zinc gallate has indirect structure due to forming hybridization between Ga-3d and 0-2p states. The threshold of interband transitions related with adsorption spectrum decreases according to the imaginary part ε_2(ω) of dielectric function. The real part ε_1(ω) of the dielectric function located at zero energy has a square fit relationship with refractive index n(0) (from 1.77 to 2.01). The absorption shoulder appears in the UV region of 350 nm for x = 0, with a red shift from x = 0 to x = 2. Energy loss function flattens out to a large extent with the enlargement of Ga concentration.