Oxygen diffusion in the orthorhombic FeNbO4 material: a computational study.

ABSTRACT

ABO4-type materials have shown significant potential for applications as luminescence and photocatalytic materials, and the orthorhombic FeNbO4 (o-FeNbO4) material has also shown excellent promise in catalytic electrodes, unlike other common ABO4 materials. However, little computational work has been carried out on the o-FeNbO4 structure, potentially because it is disordered and thus not straightforward to simulate. In this work, we first confirmed the accuracy of the force field parameters obtained from previous studies through optimizations carried out using the GULP code. Next, we found that one ordered configuration of the stoichiometric o-FeNbO4 structure dominates when analysing the probabilities of cation disorder in three supercells (2 × 2 × 1, 2 × 1 × 2, and 1 × 2 × 2). We then studied the bulk properties of this selected o-FeNbO4 through DFT calculations, including the lattice parameters, the mechanical properties and the electronic structures, where no remarkable differences were observed compared to the monoclinic FeNbO4 structure. Finally, because oxygen mobility is key to the successful application of o-FeNbO4 as an electrode material, we have simulated the diffusion pathways of oxygen through both the stoichiometric and non-stoichiometric structures, where the results show that the existence of oxygen vacancies enhances diffusion and the distribution of the Fe and Nb inside the lattice affects the energy barriers and could therefore impact the oxygen diffusion.