Highly anisotropic electronic properties of the GdBa2Ca2Fe5O13 oxide: a DFT+U study of a potential air electrode for solid oxide fuel cells

Abstract

Profound knowledge of the electronic structure of functional solids is essential to understand and optimize their properties. The current advances in electronic structure theory, together with the improvements in computing power, allow realization of affordable calculations of the electronic structure of complex solids with the aim of explaining or predicting properties of singular materials. This work presents a density functional theory study of the GdBa2Ca2Fe5O13 oxide, a potential air electrode for solid oxide fuel cells with a layered-perovskite-related structure, which presents ordering of three different coordination-polyhedra around the Fe3+ ion (FeO6 octahedra, FeO5 squared pyramids and FeO4 tetrahedra). The existence of these three different Fe3+-environments significantly impacts the electronic properties of this oxide leading to a narrow band gap. The band structure calculations of GdBa2Ca2Fe5O13 concludes that the FeO5 layers create the CB (conduction band), the FeO6-layers form the VB (valence band) and the FeO4 layers create insulating channels, leading to anisotropic electrical properties that coincide with the experimentally observed 2D magnetic, electrical, and structural characteristics of GdBa2Ca2Fe5O13.