Solid-state electrochemical cells with dense oriented thin film electrodes of La 0.5 Sr 0.5 CoO 3Ϫ␦ (LSCO) were prepared on (100) surfaces of single-crystal disks of yttria-stabilized zirconia (YSZ) by the pulsed laser deposition technique. Oxygen exchange at the electrodes was studied with alternating current impedance spectroscopy under various temperature and oxygen partial pressure conditions. Three distinctive features were observed in the impedance spectra from high to low frequency corresponding to contributions from the ionic conduction of the YSZ electrolyte, ionic transfer at the LSCO/YSZ interface, and the oxygen exchange on the LSCO electrode surface. An equivalent circuit model of the electrode process is used to fit the impedance data. The time constant for the oxygen surface exchange was derived from the impedance simulation. The surface chemical exchange coefficients, k chem , were calculated from the time constants as a function of temperature and pO 2 . k chem is 7 ϫ 10 Ϫ4 cm/s at T ϭ 700ЊC and pO 2 ϭ 1 atm. The activation energy at pO 2 ϭ 1 atm is Ϸ1.1 eV. The interfacial conductivity data were also derived from the impedance simulations as a function of temperature and pO 2 . The activation energy for the interfacial transport at pO 2 ϭ 1 atm is Ϸ1.6 eV.

Dielectric Ba0.6Sr0.4TiO3 thin films were epitaxially grown on (001) MgO by using pulsed laser ablation. Microstructure studies from x-ray diffraction and electron microscopy suggest that the as-grown films are c-axis oriented with an interface relationship of 〈100〉BSTO//〈100〉MgO. A room temperature coupled microwave phase shifter has been developed with a phase shift near 250° at 23.675 GHz under an electrical field of 40 V/μm and a figure of merit of ∼53°/dB. The performance of the microwave phase shifter based on the epitaxial Ba0.6Sr0.4TiO3 thin films on (001) MgO is close to that needed for practical applications in wireless communications.

Highly conductive perovskite La0.5Sr0.5CoO3 thin films were grown on (012) LaAlO3 by pulsed-laser deposition at different substrate temperatures. Magnetoresistance (MR) measurements show only a negative effect for the films grown at a temperature of 800 °C. However, a positive MR effect was found for the films grown at lower temperatures of 400 and 500 °C. The sign of the magnetoresistance changed from positive to negative near 150 K under an applied magnetic field of 5.0 T, and the largest positive MR of 2.6% was obtained at a temperature of 4.2 K for the film grown at 500 °C. Low-temperature magnetic hysteresis of the films was also studied, and it is suggested that the scattering of the carrier at the domain boundary may lead to the positive-MR effect.

This paper will review the recent progress of the Texas Center for Superconductivity concerning the epitaxial growth of ferroelectric Bal-,Sr,Ti03 thin films on various substrates using pulsed laser ablation. Microstructure studies from X-ray diffraction and electron microscopy suggest that the as-grown films on (001) LaAIO, and (001) MgO are c-axis oriented with excellent single crystallinity. The Rutherford Back-Scattering Spectroscopic studies indicate that the films have excellent epitaxial behavior. Microwave property measurements showed that the room temperature dielectric constant could be tuned up to 33% at 2.33 V/Km applied electric field. The coupled microwave phase shifter has achieved a phase shift of over 200" at 23.675 GHz and a figure of merit of about 55"/dB at room temperature. These results demonstrate that the epitaxial Ba,-,Sr,Ti03 thin films are close to becoming used in the practical applications for the wireless rf communications.

Photocopying permitted by liceow only 0 2000 OPA (Over\ea\ Publisher< Association) N.V. Publishcd by licenrc under the Gordon and Breach Science Publishers imprint.Ferroelectric Ba(,.,)Sr,Ti03 (x = 0.5 and 0.25) thin films were grown on (001) LaAlOj.by using pulsed laser ablation. Extensive x-ray diffraction and selected area electron diffraction reveal that the as-grown films were (001) oriented with a good in-plane relationship of BSTO // < 1 0 0 >~~0 .Rutherford Backscattering Spectroscopy ion-channeling studies suggested that the films had excellent epitaxial quality and crystallinity with an ion beam minimum yield xmin of only 2.6%. Atomically sharp interfaces were seen by cross-sectional high-resolution electron microscopy, indicated that the density of misfit dislocations was consistent with the lattice mismatch from the theoretical calculation.