Influence of titanium doping on the Raman spectra of nanocrystalline ZnAl2O4

Abstract

The local structural changes within the normal spinel structure of a ZnAl2O4 host caused by the titanium incorporation as studied by the Raman spectroscopy and computationally using the density functional theory have been analyzed. The lattice dynamics calculation of the ZnAl2O4 phonons were performed within the density functional theory for the 3D periodic crystal structures. Band structure calculations by the grid-based PAW method predicted a direct band gap in the pure ZnAl2O4 sample to be 4.732 eV, while doping with Ti4+ produced a density of states in the middle of the gap. The lattice dynamics calculations using Gaussian-type wavefunctions as basis set and a local density approximation gave a good agreement between observed and predicted Raman bands. Doping with Ti4+ causes the infrared active T1u phonons as well as the inactive phonons (T1g, A2u, Eu and T2u symmetries) to appear in the Raman spectra and breaking of the symmetry selection rules.