When neutrons and synchrotron X-Rays dance : magnetostructural correlations in rare earth perovskite cobaltates

Abstract

Substantial interest has recently been generated by rare earth cobaltate compounds as cathode materials for solid oxide fuel cells due to their substantial ionic and electrical conductivities as well as their stability at elevated temperatures. We have synthesised a wide range of single phase re perovskite-based rare earth cobaltates (Ln1-xSrxC003-d) (Ln = La3+ - Yb3+). A combination of electron and high-resolution synchrotron X-ray powder diffraction of these phases reveals a complex family of tetragonal and orthorhombic superstructures. The nature of structural and magnetic ordering relies on both the cation and oxygen vacancy distribution, which has only been as able to be successfully probed using powder neutron diffraction. Phase boundaries exists between compounds containing large, medium and small rare earths (between Nd3+ and Sm3+, and also between Gd3+ and Dy3+) and also at different Sr-doping levels. These phases show mixed valence (3+/4+) cobalt oxidation states that increases with Sr content. A range of magnetic and or electrical behaviours have been observed including ordered antiferromagnetism at elevated of temperatures (>300 K) and metallic conductivity.