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The defect chemistry of perovskite compounds is directly related to thestoichiometry and to the valence states of the transition-metal ions. Defectengineering has become increasingly popular as it offers the possibility toinfluence the catalytic properties of perovskites for applications in energystorage and conversion devices such as solid-oxide fuel- and electrolyzercells. LaFeO$_3$ (LFO) can be regarded as a base compound of the family ofcatalytically active perovskites La$_{1-x}$A$_x$Fe$_{1-y}$B$_y$O$_{3-\delta}$,for which the defect chemistry as well as the electronic and ionic conductivitycan be tuned by substitution on cationic sites. Combining theoretical andexperimental approaches, we explore the suitability for A-site vacancyengineering, namely the feasibility of actively manipulating the valence stateof Fe and the concentration of point defects by synthesizing La-deficient LFO.Formation energies and concentrations of point defects were determined as afunction of processing conditions by first-principles DFT+U calculations. Basedon the results, significant compositional deviations from stoichiometric LFOcannot be expected by providing rich or poor conditions of the oxidic precursorcompounds (Fe$_2$O$_3$ and La$_2$O$_3$) in a solid-state processing route. Inthe experimental part, LFO was synthesized with a targeted La-site deficiency.We analyze the resulting phases by X-ray diffraction and scanning electronmicroscopy, (scanning) transmission electron microscopy in combination withenergy-dispersive X-ray spectroscopy, and electron energy-loss spectrometry.Instead of a variation of the La/Fe ratio, a mixture of the two phasesFe$_2$O$_3$ and LFO was observed, resulting in an invariant charge state of Fe,in line with the theoretical results. We discuss our findings with respect topartly differing assumptions made in previous studies on this material system.

Defects and Phase Formation in Non-Stoichiometric LaFeO$_3$: a Combined Theoretical and Experimental Study