Combined neutron diffraction and atomistic modeling studies of structure, defects, and water incorporation in doped barium cerate perovskites

A series of co-doped barium cerate perovskites, Ba1-xLaxCe0.9-xY0.1+xO2.95, with 0 <= x <= 0.15, was prepared by solid-state reaction, and the structural properties were investigated using high-resolution neutron diffraction. All compositions were found to exhibit the orthorhombic Pbnm structure, although the octahedral basal plane distortion is greatly reduced on doping, accompanied with an increase in octahedral elongation. Compositions close to the solid solution limit, x = 0.1 and 0.15, are pseudo-tetragonal and pseudo-cubic and appear to be close to a phase transition, most likely to space groups Imma or I4/mcm. An anomaly in unit cell parameters occurs at low dopant concentration, 0.03 <= x <= 0.05, and was found to be reflected in reduction of the structural water uptake of the material within this compositional range. Atomistic simulations were carried out to study the energetics for dopant incorporation at A- and B-sites and water incorporation at oxygen sites. The results suggest that the reduced protonic defect concentration within the compositional range where the structural anomaly occurs might be caused by less favorable water incorporation energies.