Structure and electrical transport properties of cation-deficient derivatives of layered neodymium–barium ferrocuprocobaltite

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Layered double perovskites (LDP) based on rare earth elements, barium, and 3d-metals with high electrical conductivity and electrocatalytic activity in the oxygen reduction reaction are promising cathode materials for medium-temperature solid oxide fuel cells based on proton- or oxygen-conducting solid electrolytes. For the improvement of the functional characteristics of LDP, various strategies are used: a) creating composites based on LDP, b) the partial substitution of cations, and c) the creation of a deficiency of cations in various positions in the LDP structure. The advantage of the latter strategy is that it does not require complicating the chemical and, as a rule, phase composition of the LDP. The purpose of this study was the investigation of the effect of neodymium and barium deficiency on the structural and electrical transport characteristics of NdBaFeCo0.5Cu0.5O6–d LDP. The samples were obtained by the ceramic method and characterized using X-ray phase analysis, IR absorption spectroscopy, iodometry, electron microscopy, thermal analysis, as well as electrical conductivity and thermo-EMF measurements methods. Creation of up to 10 mol. % of vacancies in neodymium or barium sublattices had little effect on the values of the oxygen nonstoichiometry index (d) and unit cell parameters of NdBaFeCo0.5Cu0.5O6–d derivatives. owever, it led to an increase in the crystallite size (determined by the Scherrer, Williamson–Hall and size–strain methods) and the thermal stability of these phases. The values of electrical conductivity and the Seebeck coefficient of ceramics, in general, increased, and the activation energies of the electrical transfer process decreased when a deficiency of neodymium or barium was created in its structure. In the temperature range 300–700 K, the weighted mobility of charge carriers (“holes”) varied within 0.04–0.8cm2/(V·s) and increased with increasing temperature, which is typical for the polaron conduction mechanism, and their concentration varied in the range (0.1–3)·1020 cm–3, increased exponentially with increasing temperature and, in general, when a deficiency of neodymium or barium in the NdBaFeCo0.5Cu0.5O6–d structure was created