to 39 K in these reports. Here, we report our successful demonstration of the growth of 3 superconducting MgB 2 films using electron beam evaporated B precursor films followed by appropriate post-annealing. We also report results of transport property measurements on these ex-situ grown MgB 2 films. The MgB 2 films had a sharp T c (zero resistance) of 38.0 K with a ∆T c of 0.3 K and a ratio of the room temperature resistivity to the residual resistivity above T c of about 2. The resistivity decreased linearly with temperature indicating that the MgB 2 film is metallic.

KTaO 3 ͞KNbO 3 strained-layer superlattices of variable periodicity were grown by pulsed laser deposition on KTaO 3 substrates. The KNbO 3 layers were found to be strained in plane to match the substrate lattice parameter. Therefore, the applied strain is independent of the layer thickness. High-temperature x-ray diffraction was used to measure the ferroelectric-paraelectric phase transition temperature T c . For superlattice periodicity L # 5.1 nm, T c 475 K, independent of L. For L . 5.1 nm, T c increases to 825 K at L 33.8 nm. [S0031-9007(98)

YBa 2 Cu 3 O y (YBCO) films produced by the ex situ conversion of BaF 2 -based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y 2 O 3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba 2 Cu 3 O y or Ba-O-F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 m within the plane of the film in some cases. Conversely, discrete secondary phases of be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (J c ) and best film alignments for a given film thickness were found in samples where the layers of Ba 2 Cu 3 O y or Ba-O-F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y 2 Cu 2 O 5 and Ba-O-F. The data demonstrate that transient liquid phases are part of the conversion process of BaF 2 -based YBCO films. The control of both CuO segregation and the amount of liquid phases generated during the initial stages of phase formation is needed for optimizing the ex situ conversion process for high-J c coated conductors.

Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2Sr2Ca2Cu3Ox oxide-powder-in-tube conductors and (Bi, Pb)2Sr2CaCu2O8 (Bi-2212) and TlBa2Ca2Cu3Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD's). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD's are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2Cu3O7–δ films grown using laser ablation on such substrates have critical current densities exceeding 106 A/cm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

A method is described for determining the structure factor F(Q) at a scattering vector Q along a crystal truncation rod (CTR) by measuring the total power diffracted with the crystal fixed. When a detector collects the entire diffracted beam, PCTR/ P0 = pσT[λ|F(Q)|/a0 sin θ sin χ]2, where P0 and PCTR are the powers of the incident and diffracted beams, p is a polarization factor, σT is the Thompson cross section, λ is the X‐ray wavelength, a0 is the area of a two‐dimensional unit cell and θ and χ are diffractometer angles. No terms due to instrumental resolution are required for measurement of the structure factor. Simple expressions are derived relating structure factors to the integrated intensity of rocking curves employing a receiving slit wide enough to accept the diffracted beam in one direction only. Measurements employing a narrow slit are useful in measuring CTR intensity at grazing incidence (i.e. small perpendicular momentum transfer) or for specular reflection (i.e. small parallel momentum transfer). For the more general case (large perpendicular and parallel momentum transfer), accurate measurements are more easily made when the detector collects the entire diffracted beam