1PO4-60 Epitaxial Behavior and Microstructure of La_2/3Ca_1/3MnO₃ Thin Films on (001) LaAlO₃

S.Y. Chen 1, C.L. Chen 1, Z. Zhang 1, G.P. Luo 1, Y.S. Wang 1, W.K. Chu 1, C.W. Chu 1, H.-J. Gao 2, S.J. Pennycook 2, and Y. Liou 3. 1 Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, TX 77004. 2 Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6030. 3 Institute of Physics, Academia Sinica, Taipei, Taiwan 11529.

Presenting Author: S.Y. Chen

Ferromagnetic La_2/3Ca_1/3MnO₃ thin films were grown on (001) LaAlO₃ by using pulsed laser deposition. X-ray diffraction and selected area electron diffraction showed that the as-grown films were (001) oriented with good in-plane relationship. Rutherford Backscattering Spectroscopy ion-channeling studies suggested that the films had good epitaxial quality and crystallinity with the minimum yield x_min of 5.4%. Atomically sharp interfaces were seen by cross-sectional high-resolution electron microscopy. No significant misfit dislocations have been seen according to the small lattice mismatch that is less than 1%.

1PO4-61 Microwave Properties of YBCO Films Deposited on In-plane Textured CeO₂ /YSZ Buffer Layers

Kyoko Kawagishi, Kazunori Komori, Shunichi Arisawa, Masao Fukutomi, and Kazumasa Togano, 1st Research Group, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan

Presenting Author: K. Kawagishi

Recently, technological progress in the deposition and characterization of high- T_c superconductiong (HTS) films has enabled the design and fabrication of various high-T_c microwave devices. For the HTS film deposition for microwave applications, MgO is widely used as substrate. However, YBa₂Cu₃O_y (YBCO) deposition on MgO often causes mixtures of 0 and 45 degrees in-plane rotations, resulting in degradation of electrical properties, such as critical current density (J_c) and microwave surface resistance (Rs). In order to overcome this problem, we used yttria-stabilized zirconia (YSZ) and CeO₂ buffer layers between MgO and YBCO to control the in-plane epitaxy of YBCO films.

Buffer layers and YBCO films were deposited on MgO (100) using off-axis rf magnetron sputtering. Substrate temperature measurement system was improved and the deposition was performed in good reproducibility. XRD results revealed an excellent in-plane epitaxy with no evidence of misoriented grains in a YBCO/CeO₂/YSZ/MgO structure. The dielectric rod resonator method verified that reduction of Rs for HTS films obtained was accomplished. AC susceptibility, atomic force microscopy and inductively coupled plasma spectrometry have been used to analyze the film properties. An attempt was made to correlate these film properties with the measured Rs values.

1PO4-62 Chemical Vapor deposition for YBCO thin film by Liquid Delivery System

K. Cho, Xin Zhang, Naijuan Wu, and Alex Ignatiev, Space Vacuum Epitaxy Center, University of Houston, Houston, TX 99081

Presenting Author: K. Cho

The precise delivery of organometallic precursor to a CVD reactor is one of the key factors that determine thin film quality. In recent years, liquid delivery systems have become attractive because of several advantages as compared to solid precursor sublimation systems.

In this work, the liquid delivery system for YBCO and BST thin film deposition is integrated with Photo Assisted MOCVD Reactor. Ba(thd)2-tetraglyme, Sr(thd)-tetraglyme, Ti(iPr)2(thd)2 Cu(thd)2 were synthesized for precursors. These precursors are dissolved in Butyl Acetate at up to 0.1 M. All precursors are mixed together in a reservoir and delivered to a flash evaporator by a liquid pump. The flow rate is controlled from 0.1 ml/min to 1 ml/min. The liquid flow rate, evaporation temperature, reaction temperature are optimized with factorial design.

1PO4-63 Electrical conductivity relaxation analysis on epitaxial La_0.5Sr_0.5CoO_3-d thin films for solid oxide fuel cell applications

X. Chen 1, S. Wang 2, Y.L. Yang 2, L. Smith 1, N.J. Wu 1, A. Jacobson 2, and A. Ignatiev 1. 1 SVEC and MRSEC, University of Houston, Houston, TX 77204-5507. 2 Department of Chemistry and MRSEC, University of Houston, Houston, TX 77204-5507.

Presenting Author: L. Smith

The surface exchange coefficient k of La_0.5Sr_0.5CoO_3-d (LSCO) thin films was determined from electrical conductivity relaxation measurements. The LSCO thin films were deposited by pulsed laser deposition (PLD). The electrical conductivity of the films were measured at high temperature with the oxygen partial pressure concentration switches between 0.01, 0.05, 0.10, 0.30, 0.50 and 1.00atm. The k values were obtained by fitting the conductivity relaxation curves using surface limited kinetics model. The results show, that the k value increases with temperature and with the oxygen partial pressure after the switch, but is not sensitive to the initial partial pressure. After prolonged annealing at 900^oC, the k value was found to have greatly increased. The change of the thin film surface morphology with the prolonged annealing is found to be responsible for the increase of k.