Emerging proton conductivity at the interface between insulating NdGa O3 and BaZr O3

This article reports on the interplay between structural properties of the interface region and emerging proton conductivity in thin films of insulating BaZrO3 perovskite deposited by pulsed laser ablation onto NdGaO3 wide-band-gap insulators. High-resolution transmission electron microscopy and surface x-ray diffraction reveal the presence of a large number of misfit dislocations at the interface, allowing the full relaxation of the epitaxial strain. An analysis of the x-ray diffraction patterns reveals strain relaxation that occurs over a thickness of about 3 nm, equally divided between the film and the substrate. Electrical impedance spectroscopy measurements show a sizeable proton conductance that can mainly be attributed to the defective interface. Assuming that proton conduction occurs in the interface layer, values of interface conductivity of about 0.5 S/cm at 650 degrees C are estimated with an activation energy of about 0.86 eV. Experimental findings are explained assuming that the defective interface layer can accommodate a very large concentration of carriers whose mobility is somewhat hindered by the high concentration of structural defects at the interface.