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The transport properties of double perovskite LaBaCo2O5.5+δ thin films with different thicknesses were systemically studied. A thin (7 nm in thickness), disordered LaBaCo2O5.5+δ layer was formed at the interface between the film and substrate. The films had a typical semiconductor behavior with antiferromagnetic and ferromagnetic behavior coexisting at low temperature. Although the Curie temperature was independent of the film thickness, the coercive fields and magnetizations increase with increasing the film thickness. An ultra large magnetoresistance effect value of about 44% was obtained at 60 K for the film of 82 nm.

Symmetric half cell structures of highly epitaxial PrBaCo2O5+δ (PBCO)/Gd0.8Ce0.2.2O2:Y0.08Zr0.92O2/PrBaCo2O5+δ thin films were designed and fabricated on (001) LaAlO3. Microstructural studies indicate that the multilayer films have excellent single-crystal quality and epitaxial nature. The electrochemical impedance spectroscopy measurements reveal that the PBCO film electrodes have a polarization resistance as low as 0.109 Ω cm2 at 597 °C in air and an ultrafast surface exchange coefficient (0.006 cm/s at 598 °C) with low activation energy (0.77 eV). The low polarization resistance and rapid surface oxygen exchange kinetics suggest that the PBCO can be an excellent cathode material for intermediate-temperature solid oxide fuel cells.

This research was partially supported by Department of Energy under Grant No. DE-FG26-07NT43063, the National Science Foundation under Grant No. NSF-NIRT-0709293, the Texas ARP Program under Grant No. 003656-0103-2007, the State of Texas through the Texas Center for Superconductivity at the University of Houston, and the South Texas Technology Management Program.

The (LaBa)Co2O5+δ thin films were grown on (001) SrTiO3 single crystal substrates by using pulsed laser deposition. Microstructure studies from x-ray diffraction and electron microscopy show that the films have good epitaxial quality with a-axis orientation and sharp atomic interface. Transport property and isothermal magnetoresistance measurements have been used to understand the physical properties of the films with anomalous magnetic phenomena and the largest reported magnetoresistance value of 19% at 40 K.