Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide

Abstract

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation.

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…Thus, the development of high-performance cathodes has become the REVIEW (3 of 34) 1500537 wileyonlinelibrary.com biggest obstacle to reduction of operational temperature of SOFCs and has attracted the most attention in current SOFC research. [ 35,36,[74][75][76][77] During the past several decades, numerous strategies have been investigated to increase the performance of SOFC cathode at reduced temperatures, from new materials development to advanced synthesis and microstructural optimization. [ 30,53,[78][79][80][81][82][83][84][85] To date, there are a number of good reviews that focus on electrodes for oxygen reduction reaction (ORR) in SOFCs, as listed in Table 1 .…”

“…To date, many developed cathode materials with high activity for ORR contain alkaline earth metal elements. [ 35,36,75,81 ] Several review papers about these cathode materials recently appeared in the literature. [ 131,132 ] Such cathode materials have high oxygen vacancy concentration, high electronic conductivity, and fl exible composition.…”

“…75 Pérez-Flores et al reported a new series of A-and B-site ordering in the A-cation-defi cient perovskite cathodes of La 2-x NiTiO 6-δ (0 ≤ x < 0.20). [ 198 ] Ni and Ti ordered over the B-site and, unusually, for x > 0, the A-site ions also ordered along the c axis in alternate La-rich and ᮀ-rich layers (where ᮀ represents a vacancy).…”

Grand Challenges in Fuel Cells: Materials Issues at all Length Scales

“…As elucidating examples of induced mixed ionic and electronic conduction, with a variety of potential applications, we recall here the classical doping effects in fluorite-type solid solutions like ZrO 2 -CeO 2 -Y 2 O 3 (Cales and Baumard, 1984) to generate both oxide-ion and electronic conductivity. Moving to other length scales, we have recent examples of tunable ionic and electronic conductivity based on structural or microstructural effects in perovskite-type oxides like (Ba,Sr)(Co,Fe,Mo)O 3-δ (Demont et al, 2013) or (La,Sr)(Ga,Mg)O 3-δ (Gomes et al, 2006), and also in conventional cermets used as SOFC anodes (Iwaia et al, 2010). In the first case, formation of distinct nanosized domains inside grains yields the unusual combination of properties.…”

“…These nano-domains are formed due to cation ordering in specific perovskite-type oxides like (Ba,Sr)(Co,Fe,Mo)O 3-δ . Drawing inspired in (Demont et al, 2013). Possible tuning of properties at nanosized level has an obvious immense potential in fuel cell and allied applications.…”