YBa2Cu3O7 Films Research Articles

Use of real-time Fourier transform infrared reflectivity as an in situ monitor of YBa2Cu3O7 film deposition and processing

Fourier transform infrared reflectivity (FTIR) has been utilized as an in situ, real-time diagnostic during high-rate, e-beam deposition of YBa2Cu3O7 (YBCO). The results demonstrate the great utility of FTIR as an in situ monitor of YBCO deposition and postdeposition processing. They also point to a completely different picture of the nature and associated kinetic and thermodynamic pathways of the high-rate, e-beam process, both during deposition and as a function of subsequent trajectories through temperature and oxygen pressure space.

Enhancement of Current Carrying Capability in MOD-Processed YBCO Films Using Chemical Doping

Many efforts have been made to improve the current carrying capability of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (YBCO) films by introducing pinning centers using a variety of techniques. In this study, we have succeeded in producing Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Sm doped YBCO films for the development of coated conductors by a metal-organic deposition method using trifluoroacetates (TFA-MOD). Jc exceeding 5 MA /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K and self field was obtained in Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> doped YBCO film. Also it was found that YBCO films with Sm substituting for Y have shown an improved critical current density characteristic over a wide range of magnetic fields. A Jc of 0.25 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 3 T and 77 K was obtained which is more than 10% of the zero-field Jc. Similar results were obtained in BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> doped YBCO films. Additionally, TEM analysis was performed to study the microstructures and the pinning mechanisms. The results indicate that significant enhancement of self-field and in-field Jc of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Sm doped YBCO films may be due to introducing nano-scaled Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles, nano-scaled 90deg rotated Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> domains and BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanodots by different chemical doping, respectively. This indicates that chemical doping is a promising approach for enhancement of current carrying capability of YBCO coated conductors.

${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Coated Conductor Grown by Hybrid Liquid Phase Epitaxy

The hybrid liquid phase epitaxy (HLPE) approach has the potential to be a high rate-low cost process. This deposition process is used to grow epitaxial YBa2Cu3O7 (YBCO) films in the presence of a thin (100 to 500 nm) liquid BaO-CuO flux layer. Despite the presence of the molten flux, YBCO growth is found to be feasible on technical substrates because of the limited dissolution of the buffer layer in the thin flux layer. The high atom mobility at the growing interface under the liquid flux enables high growth rates (demonstrated to be greater than 10 nmldrs-1 in a wide temperature regime and predicted to be up to ~5 nmldrs-1). We report results on HLPE YBCO films grown on (100) strontium titanate and textured technical substrates such as rolling-assisted biaxially textured substrates (RABiTS) and ion-beam-assisted-deposited (IBAD) MgO. High values of the critical temperature above 90 K and critical current ~400 A per cm width for 3 mum thick films on single crystal substrates and promising high values on technical substrates are obtained. Furthermore, there is potential for making thicker films of the same quality since film density is maintained with thickness. Angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy are also reported. The angular and field dependence of critical current density are similar to standard PLD (pulsed laser deposition) films. Although the films are of high epitaxial quality they contain yttria precipitates which are possible sources of flux pinning centers.

Long Baseline 2nd-Order High-$T_{\rm c}$ SQUID Gradiometer Made From a Single-Layer ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Film

We have fabricated a 30 mm long baseline 2nd-order SQUID gradiometer from a single-layer YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> film. The gradiometer was patterned from a YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> film on a sapphire substrate by argon ion milling with a photoresist mask. The device had an overall size of 70.2 mm times 10.6 mm and a baseline of 30 mm with three parallel-aligned 10.2 mm times 10.2 mm pickup loops coupled directly to a dc SQUID to measure part <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> /partx <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Josephson elements of the device were YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> nanobridges which were made by a focused ion beam technique. Design of the gradiometer was based on the same rules as those of 2.9 mm short baseline gradiometers. Gradient sensitivity of the gradiometer was estimated to be ~ 1.8 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , which was equivalent to a field noise of 160 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , for an intrinsic SQUID flux noise of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> Phi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . We also studied the transition properties of the YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> nanobridge. The bridge showed an superconductor- normal metal-superconductor (SNS) behavior with the top Au layer intact and an superconductor-insulator-superconductor (SIS) behavior with Au removed. We believe that the Josephson nature of the bridge is ascribed to naturally formed grain boundaries in the bridge.

Microstructure of Epitaxial Y123 Films on ${\rm CeO}_{2}$-Buffered YSZ Prepared by Fluorine-Free MOD

Epitaxial YBa2Cu3O7 (Y123) films have been prepared by fluorine-free metalorganic deposition (MOD) using a metal acetylacetonate-based coating solution on cerium oxide (CeO2: 40 nm)-buffered yttria-stabilized zirconia (CbYSZ) substrates. The 210-nm-thick Y123 film demonstrated a high critical current density (Jc), the average Jc being 4.5 MA/cm2 at 77.3 K using an inductive method. However, with increasing thickness the Jc values decreased; the average Jc was 3.4 and 2.2 MA/cm2 for 400-nm- and 550-nm-thick films, respectively. In low-magnification cross sectional transmission electron microscopy (XTEM) images for the films, the stripe-like contrast due to the c-axis orientation of Y123 was clearly seen from the interface with CeO2 to the surface. The whole c-axis-oriented Y123 layers were very dense even in the 550-nm-thick film. Full width at half maximum (FWHM) of Deltaomega for the 308/038 reflections in XRD omega - 2thetas scanning decreased with increasing film thickness. High resolution XTEM images of the 550-nm-thick film showed wavy c-planes of Y123 due to the short stacking faults near the interface with CeO2 buffer and near the surface whereas the c-planes were very flat but contained long stacking faults in the middle part of the film. It is suggested that the absence of wavy stacking faults, which probably work as pinning centers, decreased Jc in the thicker films. Further decrease in Jc in the 550-nm-thick film is presumably caused by the roughness in the outer layer near the surface.

Preparation of YBCO films by an excimer-laser-assisted MOD by scanning irradiation

Epitaxial YBa2Cu3O7 (YBCO) films were prepared on cerium oxide-buffered sapphire (r-cut α-Al2O3) substrates by an excimer-laser-assisted metalorganic deposition (ELAMOD) using a scanning substrate mode. The substrate surface was scanned under homogenized KrF excimer laser beam irradiation after application of a fluorine-free ingredient solution. The ELAMOD process has brought about the advantages of shorter heating time as well as higher critical current density (Jc) of the YBCO films. The Jc values over 6MA/cm2 were measured by an inductive method at 77.3K for the laser-irradiated areas. The scanning laser irradiation is considered to produce a desirable precursor for crack free films with high-Jc and to shorten the total time of heat treatment, in which three metal components are well-dispersed in short time. Such a precursor has contributed to prevent the occurrence of impurity phases, resulting in the high-Jc YBCO films. The X-ray diffraction measurement of the irradiated area clearly showed a complete c-axis-oriented YBCO and no impurity phases, whereas a-axis-oriented YBCO was dominant in the area without irradiation. The ELAMOD process using the scanning substrate mode has a potential ability to apply to continuous production of the large-area films or long tapes of YBCO.

Preparation of large-size Y123 films on CeO2-buffered sapphire substrates by MOD using a low-cost vacuum technique

High-Jc YBa2Cu3O7 (Y123) films with good homogeneity have been obtained on CeO2-buffered sapphire substrates by metal organic deposition (MOD) using a low-cost vacuum technique; only nitrogen gas and air instead of a high-purity gas mixture of argon and oxygen were supplied in the high-temperature heat treatment. A 2cm×12cm rectangular Y123 film was prepared in a large-size tube furnace with uniform temperature zone. The total pressure and oxygen partial pressure in the furnace were controlled by the flow rates of nitrogen and air and by evacuation speed of a rotary pump. The apparent inductive-Jc values, except those at a few positions near the film edges, were within 3.0±0.3MA/cm2, i.e., the fluctuation of Jc was within ±10% of the average. Comparison of the spatial distributions of Ic, film thickness and XRD intensity of Y123 suggests that the crystallinity of Y123 and Jc values at local points are uniform over the film and the thickness distribution affects the local Ic values, or apparent Jc distribution.

Universal temperature scaling of flux line pinning in high-temperature superconductingthin films

Dissipation-free current transport in high-temperature superconductors is one of the mostcrucial properties of this class of materials which is directly related to the effective inhibition offlux line movement by defect structures. In this respect epitaxially grown thin films ofYBa2Cu3O7−δ (YBCO) are proving to be the strongest candidates for many widescale applications thatare close to realization. We show that the relation between different defect structures andflux line pinning in these films exhibits universal features which are clearly displayed in adetailed analysis of the temperature-dependent behaviour of local critical currents. Thisallows us to identify different pinning mechanisms at different temperatures to beresponsible for the critical currents found. Additionally, the presence of grainboundaries with very low misorientation angles affects the temperature stability ofthe critical currents, which has important consequences for future applications.

Substrate-induced current anisotropy in YBa 2Cu 3O 7− δ thin films

The defect structure in thin epitaxial films of YBa 2Cu 3O 7− δ is strongly dependent on the substrate. Using vicinal cut substrates can lead to an anisotropic critical current density in the film plane. Temperature-dependent measurements using quantitative magneto-optics make it possible to investigate current densities along different directions independently. By applying a step-wise power-law to the data, different current limiting mechanisms could be identified.

Enhanced flux pinning in YBa2Cu3O7 layers by the formation of nanosized BaHfO3 precipitates using the chemical deposition method

Both a high critical current density and a cost-competitive, easily upscalable procedure are among the most critical requirements for coated conductors. In this work, a low-cost method based on the trifluoroacetic acid process was used to prepare nanosized BaHfO3 particles inside a YBa2Cu3O7 film matrix. The inclusions have a perovskite structure and grow epitaxially in a cube-on-cube relationship. A drastically improved pinning force density and high irreversibility fields in the YBa2Cu3O7 layers were found and are discussed in respect to the Hf doping level in the precursor solutions, which resulted in an increased nanoinclusion content.

Effect of oxygen stoichiometry and microstructure on superconducting properties of YBaCuO films

Microstructure and oxygen stoichiometry of YBaCuO films manufactured by laser ablation are investigated. Dependence of the specific electrical resistivity and superconducting parameters of films on microstructure and oxygen stoichiometry is demonstrated. Conditions of deposition are determined, under which films with minimum microstructure defects and good conducting properties are formed.

Crossover between Channeling and Pinning at Twin Boundaries inYBa2Cu3O7Thin Films

The critical current (Jc) of highly twinned YBa2Cu3O7 films has been measured as a function of temperature, magnetic field, and angle. For much of the parameter space we observe a strong suppression of Jc for fields in the twin boundary (TB) directions; this is quantitatively modeled as flux-cutting-mediated vortex channeling. For certain temperatures and fields a crossover occurs to a regime in which channeling is blocked and the TBs act as planar pinning centers so that TB pinning enhances the overall Jc. In this regime, intrinsic pinning along the TBs is comparable to that between the twins.

High Tc Josephson Nanojunctions Made by Ion Irradiation: Characteristics and Reproducibility

Reproducible High Tc Josephson junctions have been made in a rather simple two-step process using ion irradiation. A microbridge 1 to 5 micrometers wide is firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7 film through a gold mask such as the unprotected part becomes insulating. A lower Tc part is then defined within the bridge by irradiating with a much lower dose through a 20 nm wide narrow slit opened in a standard electronic photoresist. These planar junctions, whose settings can be finely tuned, exhibit reproducible and nearly ideal Josephson characteristics. Non hysteretic Resistively Shunted Junction (RSJ) like behavior is observed, together with sinc Fraunhofer patterns for rectangular junctions. The IcRn product varies with temperature ; it can reach a few mV. The typical resistance ranges from 0.1 to a few ohms, and the critical current density can be as high as 30 kA/cm2. The dispersion in characteristics is very low, in the 5% to 10% range. Such nanojunctions have been used to make microSQUIDs (Superconducting Quantum Interference Device) operating at Liquid Nitrogen (LN2) temperature. They exhibit a very small asymmetry, a good sensitivity and a rather low noise. The process is easily scalable to make rather complex Josephson circuits.

Features of vortex pinning and magnetic flux creep in epitaxial thin films of high-Tc superconductor YBa2Cu3O7−δ near the critical temperature

The temperature dependence of the dynamic relaxation rate in YBa2Cu3O7−δ epitaxial thin films is investigated in the temperature range from 77K to the critical temperature Tc with and without an applied dc magnetic field, and the dependence on the dc field at 77K is measured at fields up to 45mT. It is shown that the experimental results are in good agreement with the vortex lattice pinning model proposed previously which considers the main pinning centers in thin films to be threading dislocations on a network of low-angle grain boundaries. From the results of the experiment it is concluded that the influence of thermal fluctuations on the vortex pinning by threading dislocations and on the magnetic flux creep near Tc is not so crucial as in the case of pinning by extended linear defects in thick films or single crystals. Estimates are made which show that this fact can be explained by a transformation of the Abrikosov vortices into Pearl vortices when the magnetic field penetration depth becomes greater than the film thickness as the temperature approaches a critical value. Because of this, the mechanisms of pinning and flux creep in thin films are of a substantially collective character even in extremely weak magnetic fields and at temperatures very close to Tc.

Laser scanning microscopy of guided vortex flow in microstructured high-Tc films

We report the visualization of guidance of vortices by artificial microholes (antidots) in superconducting thin films using a low-temperature laser scanning microscope. Previously, guided motion of vortices via tilted rows of antidots in YBa2Cu3O7 films was detected indirectly by using resistive Hall-type measurements. Here we prove that vortices are steered between antidots into a priori chosen direction by imaging of resistive photoresponse with a spatial resolution down to about 1μm. We observe predominant paths for vortex motion. Vortices are nucleated and annihilated at antidots, i.e., antidots define starting and ending points of predominant vortex paths. Depending on the misorientation angle between rows of antidots and the current-driven direction of vortex motion, different channels dominate in antidot-guided vortex motion. Our experimental results can be explained by the n-channel model. Finally, we present direct measurements of the local critical currents. This technique can be used as a quantitative method for the analysis of vortex motion in micropatterned thin films.

Effects of magnetic substrates on ac losses of YBa2Cu3O7 films in perpendicular ac magnetic fields

Effects of a magnetic substrate on the ac losses of superconducting films were investigated by measuring the losses for octagonal disks of an YBa2Cu3O7 layer on a magnetic Ni–5at.% W substrate in perpendicular ac magnetic fields at 20Hz and 77K. At low fields, the losses depended on ac magnetic field amplitude B and film thickness t as ∝B3∕t instead of ∝B4∕t3 for a superconducting film on a nonmagnetic substrate. These results are described by considering the formation of a virtual infinite stack of superconducting films due to the magnetic mirror effect.

Drastic improvement of surface structure and current-carrying ability in YBa2Cu3O7 films by introducing multilayered structure

Much smoother surfaces and significantly improved superconducting properties of relatively thick YBa2Cu3O7 (YBCO) films have been achieved by introducing a multilayered structure with alternating main YBCO and additional NdBCO layers. The surface of thick (1μm) multilayers has almost no holes compared to YBCO films. Critical current density (Jc) has been drastically increased up to a factor &amp;gt;3 in 1μm multilayered structures compared to YBCO films over entire temperature and applied magnetic field range. Moreover, Jc values measured in thick multilayers are even larger than in much thinner YBCO films. The Jc and surface improvement have been analyzed and attributed to growth conditions and corresponding structural peculiarities.

Structure, pinning and supercurrent in YBa2Cu3O7 films and ReBa2Cu3O7 multilayers

High quality YBa2Cu3O7 (YBCO) films and multilayers of ReBa2Cu3O7 superconductors, where Re is rare earth elements (Y and Nd), have been prepared by pulsed laser deposition. Pinning characteristics of the structures obtained have been analysed and attributed to growth conditions and corresponding structural peculiarities. Relatively thick (∼1 µm) multilayers exhibit better performance than mono-layer YBCO films having arbitrary thickness. differences in the films and multilayers are discussed in terms of their structure homogeneity and defects induced by the growth of the layers.

Structural aspect of high-Jc MOD-YBCO films prepared on large area CeO2-buffered YSZ substrates

YBa2Cu3O7 (YBCO) film was prepared by fluorine-free metalorganic deposition (MOD) on a 2-inch-diameter CeO2-buffered yttria-stabilized zirconia (CbYSZ) substrate. The MOD-YBCO films on a flat CbYSZ prepared using a metal acetylacetonate-based coating solution demonstrated high critical current density (Jc), the average being higher than 4 MA/cm2 at 77.3 K and in a self field using an inductive method. The Jc distribution was uniform in the whole area of the MOD-YBCO films on the large size substrates. Cross sectional transmission electron microscopic images of the MOD-YBCO film exhibited a very smooth CeO2/ YSZ and CeO2 buffer layer/ YBCO film interfaces. Both the buffer and the YBCO layers were dense; however, a small amount of (100)-oriented YBCO occurred inside the matrix of (001)-oriented YBCO layers. Also, some distinct dislocations were observed at the CeO2/ YBCO interface. From around the stepped surface of the CeO2 buffer layer there seemed to grow a slightly distorted (001)-oriented YBCO domain, however, the domain restored its (001)-oriented periodicity in the region at some distance above the steps. Such growth mode is considered to correlate the high Jc of the MOD-YBCO film with very small average roughness of CeO2 buffer layer.

Microstructural observations of epitaxial Y123 films on CeO2-buffered sapphire by metal organic deposition

Epitaxial YBa2Cu3O7 (Y123) films were obtained on CeO2-buffered sapphire substrates by a fluorine-free MOD process. A 170-nm-thick homogeneous film revealed a high critical current density (Jc > 4 MA/cm2) at 77 K, whereas a 320-nm-thick film had a low Jc of 0.7 MA/cm2. Both of the films have neither a-axis orientation nor BaCeO3 phase by x-ray diffraction. In this article, the microstructures of these Y123 films were observed by crosssectional transmission electron microscopy. The epitaxial c-axis layers were observed successively from the interface with CeO2 buffer to the surface. Selected area diffraction (SAD) exhibited that the orientation relationship among the Y123, CeO2-buffer and sapphire substrate was: Y123(001)[110] ∥ CeO2(100)[100] ∥ Al2O3(-1012)[1-210]. The impurity phase on the surface was revealed to be a CuYO2 compound by energy dispersive X-ray spectroscopy and SAD. The Y123 grains on the surface of the 320-nm-thick film were somewhat inclined to the epitaxial Y123 layer; this is one of the reasons for degraded Jc in the thicker films.