Multifunctional brownmillerites Kbife2o5 and ca2fe2o5 for energy and Environmental applications

Abstract

In recent years multifunctional brownmillerites have gained enormous attention in the field of next generation photocatalysis and photovoltaics (PV). These multifunctional brownmillerites are advantageous over regular perovskite compounds due to their lower optical bandgap, which is an important requirement for photoactive applications. Brownmillerites, which are derived from perovskite structures (ABO3) and have an empirical formula A2B2O5, boast of lower optical bandgaps as compared to many perovskites. Typical perovskite structured materials with corner sharing BO6 octahedra, lose their dielectric and magnetic properties at higher temperatures. Brownmillerite structured (A2B2O5) compounds with their oxygen deficient nature need to be explored as an alternative. A2B2O5 like structures possess oxygen deficiency and corner sharing BO6 octahedra alternate with rows of corner sharing BO4 tetrahedra. Typically, Fe-based brownmillerite compounds contain FeO4 tetrahedra leading to the occurrence of lower optical bandgaps unlike Fe based perovskites which consist of FeO6 octahedra only. The lower bandgap in Fe based Brownmillerite compounds is attributed to the presence of shorter Fe-O bond lengths and high covalence in FeO4 tetrahedron as compared to FeO6 octahedron. Oxygen deficiency in the brownmillerite structure also leads to lower optical bandgap (Eg), which is a major advantage over typical ABO3 perovskite structures. Perovskite and brownmillerite structured metal oxides are potential materials for catalytic applications. The catalytic activity in these metal oxides is attributed mostly to the presence of B-site transition metal cation and has already been related to the number of d-electrons. Enhanced catalytic activity by perovskites with oxygen vacancies motivates the fact that brownmillerites (with ordered oxygen vacancies) can act as potential catalytic material newline newline newline