Electronic Structures of CexHf1-xO2 (x=0.5 and 0.75) Mixed Oxides

Abstract

Density functional theory (DFT) calculations of electronic energy bands of Ce_xHf_1-xO₂ (x=0.5 and 0.75) are investigated within the generalized gradient approximation (GGA) and taking into account relativistic contributions. Nonlinear core corrections terms are used. Our plotted band structures show that the valence bands are separated from the conduction bands by an indirect band gap of 4.14eV, from X to Γ and direct band gap of 4.18eV at X for Ce_0.75Hf_0.25O₂. For Ce_0.5Hf_0.5O₂, the indirect band gap is 3.56eV from X to Γ and direct band gap of 3.84eV at Γ. Hence, the fundamental band gap in these alloys are indirect. We found a direct band gap of 5.90eV for CeO₂ at the Γ point, in good agreement with experiment. We also calculated lattice parameters of 5.28Ǻ and 5.37Ǻ for Ce_0.5Hf_0.5O₂ and Ce_0.75Hf_0.25O₂ respectively. Hf doping in ceria (CeO₂) results in reduced band gap compared to pure ceria. From the density of states (DOS) plot, the band gap is formed predominantly from O2p and (Ce, Hf)5d states from valence and conduction bands respectively. The calculated wide band gap of the oxides show that they are active in ultraviolet (UV) radiation and so can be applied as UV blockers.

Keywords: Density functional theory, Lattice parameter, Band structure, Band gap, Density of states