The effects of A-site non-stoichiometry and crystallinity on the proton conductivity of anhydrous proton conducting yttria-doped barium zirconate (BYZ) thin film were investigated. The membranes were fabricated by atomic layer deposition (ALD) as it allows tailoring and varying the concentration of barium. Electrochemical impedance spectroscopy was conducted to investigate the ionic conductivity according to the stoichiometry and crystallinity of the ALD BYZ thin films. (C) 2013 Elsevier B.V. All rights reserved.