Figure 1: Double perovskite crystal structure and cobalt crystal field.
From: Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution
(a) Schematic representation of (Ln0.5Ba0.5)CoO3−δ double perovskites (LnBaCo2O5+δ′ with δ′=1−2δ) showing the ordering of Ln and Ba cations and the formation of oxygen deficiency in the LnO1−δ planes. This ordering is reflected by the doubling of the c parameter compared with ideal cubic perovskites, resulting in ap × ap × 2ap lattice parameters (ap being the lattice parameter of cubic perovskite indexed in Pm-3m space group). The structure has (b) octahedral (Oh) and (c) square pyramidal (C4v) symmetry for Co ions, with different crystal-field splitting of d-electron states for the different coordination symmetries.
