Highly anisotropic electronic properties of the GdBa ₂ Ca ₂ Fe ₅ O ₁₃ oxide: a DFT+ <i>U</i> study of a potential air electrode for solid oxide fuel cells

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.