Reported and predicted structures of Ba(Co,Nb)1−δO3 hexagonal perovskite phases

Abstract

The Extended Module Materials Assembly computational method for structure solution and prediction has been implemented for close-packed lattices. Exploring the family of B-site deficient materials in hexagonal perovskite barium cobalt niobates, it is found that the EMMA procedure returns the experimental structures as the most stable for the known compositions of Ba₃CoNb₂O₉, Ba₅Nb₄O₁₅ and Ba₈CoNb₆O₂₄. The unknown compositions Ba₁₁Co₂Nb₈O₃₃ and Ba₁₃CoNb₁₀O₃₉, having longer stacking sequences, are predicted to form as intergrowths of Ba₃CoNb₂O₉ and Ba₅Nb₄O₁₅, and are found to have similar stability to pure Ba₃CoNb₂O₉ and Ba₅Nb₄O₁₅, indicating that it is likely they can be synthesised.