First-principles calculations of structural, electronic and optical properties of ZnGaxAl2−xO4 spinel-type oxides

• The bond strength (Al–O, Ga–O) of ZnGaxAl2−xO4 is weaker than that of Al2O3 and Ga2O3 based on the comparison bond length.
• The absorption edges from 350 nm for x = 0, 650 nm for x = 2 with red shift are in agreement with theoretical and experimental value, as well as the data derived from the formula (4).
• The real part ε1(ω) of the dielectric function located at zero energy has a square fit relationship with refractive index n(0).
• The index n(0) from 1.77 to 2.01 are suit for UV reflective coatings.
• The peak of energy loss becomes flatter from x = 0 to x = 2. It indicates that the ZnAl2O4 is better candidate than ZnGaxAl2−xO4 (0 < x) for optical storage materials.

The structural, electronic and optical properties of the perfect ZnGaxAl2−xO4 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 Al2O3 and Ga2O3, 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 O-2p states. The threshold of interband transitions related with adsorption spectrum decreases according to the imaginary part ɛ2(ω) of dielectric function. The real part ɛ1(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.