The Electronic and Thermodynamic Properties of Ca doped LaFeO3 – A First Principles Study Using Density Functional Theory

摘要

Density functional theory (DFT) was used to evaluate the electronic and thermodynamic properties of Ca-doped LaFeO3 (La1-xCaxFeO3-y). La1-xCaxFeO3-y exhibits ionic (O2- anions) and electronic conductivity at high temperatures and has potential applications in gas separation, syngas production and solid oxide fuel cell cathodes. DFT is a computational technique based on the First Principles of physics, derived from the theory of quantum mechanics. DFT approximates the ground state energy of a system and can subsequently determine many bulk properties such as lattice constants, magnetic states, band gap, density of states (DOS) and defect formation energy (DFE).The calculated ground state structure for LaFeO3 was assumed to be orthorhombic and the optimized magnetic state was the G-type antiferromagnetic. The Hubbard U (DFT+U) method successfully corrected the underestimated band gap and magnetic moment of Fe for the orthorhombic LaFeO3 system. The electronic structures (DOS) indicated the substitution of Ca atoms introduced holes; while an oxygen vacancy introduced extra electrons and the combination of these defects annihilate the defect states. The calculated DFE indicated the addition of a Ca atom is energetically favorable, but the formation of an oxygen vacancy was energetically very unfavorable. The combination of the two defects lowered the DFE considerably, indicating that the ionic conductivity in LaFeO3 can be substantially increased with the introduction of Ca atoms.