The effect of crystallinity on proton conductivity in amorphous, single crystal and polycrystal yttrium-doped barium zirconate (BYZ) thin films grown 120 nm in thickness on amorphous (quartz) and single crystal MgO (100) substrates has been studied. The conductivity was measured in the temperature range of 150 similar to 350 degrees C. By altering the film deposition temperature, varying degrees of crystallization and microstructure were observed by x-ray diffraction and transmission electron microscopy. The epitaxial BYZ film grown on MgO (100) substrate at 900 degrees C showed the highest proton conductivity among other samples with an activation energy of 0.45 eV, whereas polycrystalline and amorphous BYZ films showed lower conductivities due to grain boundaries in their granular microstructure. (C) 2011 Elsevier B.V. All rights reserved.