Structural properties of mixed conductor Ba 1- x Gd 1- y La x + y Co 2 O 6- δ .

Ba 1- x Gd 1- y La x + y Co 2 O 6- δ (BGLC) compositions with large compositional ranges of Ba, Gd, and La have been characterised with respect to phase compositions, structure, and thermal and chemical expansion. The results show a system with large compositional flexibility, enabling tuning of functional properties and thermal and chemical expansion. We show anisotropic chemical expansion and detailed refinements of emerging phases as La is substituted for Ba and Gd. The dominating phase is the double perovskite structure Pmmm , which is A-site ordered along the c -axes and with O vacancy ordering along the b -axis in the Ln-layer. Phases emerging when substituting La for Ba are orthorhombic Ba-deficient Pbnm and cubic LaCoO 3 -based R 3̄ c . When La is almost completely substituted for Gd, the material can be stabilised in Pmmm , or cubic Pm 3̄ m , depending on thermal and atmospheric history. We list thermal expansion coefficients for x = 0-0.3, y = 0.2.