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0 (T) is its pressure derivative. Very often only simple power laws are used for the temperature dependence of these “parameters” without any theoretical foundation. However, the thermo-physical properties of solids can be modelled much more reliably by using the thermodynamic approach, which starts from a reasonable model for the volume dependence of the groundstate (zero temperature or static lattice) energy E0(V) of the ideal lattice and adds appropriate terms to the free energy for the various (temperature dependent) excitations from phonons Fph(V,T), from the

The preparation of several 100 nm thick La 2 Zr 2 O 7 (LZO) buffer layers on biaxially textured Ni-5 at.%W substrates using chemical solution deposition is studied. This oxide material is currently of great interest for the fabrication of YBa 2 Cu 3 O 7− x (YBCO) coated conductors. Buffer layers for these coated conductors are required to have thicknesses greater than 100 nm in order to guarantee a sufficient barrier function against metal diffusion from the substrate. In this work, single LZO buffer layers with thicknesses exceeding 200 nm have been prepared. Detailed investigations were carried out in order to study the texture development with increasing thickness as well as the microstructure of these layers. Independent of the thickness, high quality buffer layers showing a distinct biaxial texture up to the surface, smooth surfaces, and a sufficient barrier function against Ni diffusion from the substrate have been reproducibly obtained. The high performance of these chemical solution derived LZO buffer layers was confirmed by a YBCO critical current density J c of 1.0 MA/cm 2 (77 K, 0 T) achieved for a coated conductor sample with a layer sequence YBCO/CeO 2 /LZO(CSD)/Ni-5 at.%W where CeO 2 and YBCO were deposited by pulsed laser deposition.

The Equations of State for Cu, Ag, and Au in the sub-TPa region are constraint by correlated fits of all the thermo-physical data at ambient pressure and by theoretical estimates of the intrinsic anharmonicities. A hierarchy in the parameters provides a robust fitting procedure with typical accuracies of the finally calculated pressures of probably better than 1% at temperatures to the melting curve and pressures into the TPa-region.

Epitaxial Nb/SmCo 5 and Nb/FePt thin films were prepared by pulsed laser deposition under UHV conditions to investigate the influence of the magnetic stray fields on the superconductive properties of the Nb layer. These two systems differ in their growth mode (smooth and continuous growth in the case of SmCo 5 versus island growth for FePt grains) and in their direction of the magnetic easy axis. Whereas the magnetization of the SmCo 5 domains is oriented parallel to the film plane, the magnetization of FePt grains is aligned perpendicular to the film plane which results in two different stray field geometries.

Polycrystalline samples of MgB2 doped with reactive nanostructured carbon were synthesized by pressure assisted sintering of mechanically alloyed precursors. Varying the nominal carbon concentration from x = 0 to 0.316, the effects of carbon doping on the lattice parameter, lattice strain, actual amount of incorporated carbon (xactual), grain size, normal state resistivity (?), connectivity, superconducting transition (Tc), critical fields (Birr and Bc2) and critical current density (Jc) as well as the pinning force (Fp) were evaluated. An evident solubility limit of carbon within the MgB2 matrix, forming MgB2?xCx with an xactual?0.125, was observed. In addition to the carbon saturation the superconducting properties, e.g.?Tc, Bc2 and Jc, also reflect saturation effects with respect to the actual carbon concentration. Improved electron scattering in MgB2?xCx seems responsible for the observed enhancement of Bc2 to 11.4?T at 20?K. On the other hand, calculations of the flux-pinning forces show a dramatic decrease of Fp,max with increasing carbon concentration. Therefore we conclude the observed improvement in critical current density at applied fields >6?T to result mainly from the raised upper critical field.

Y2O3 nanoparticles prepared by an inert gas phase condensation process were used to introduce artificial pinning centres in YBa2Cu3O7−δ thin films. The areal density of the particles was varied between 120 and 4200 particles µm−2 without changing the mean particle diameter of approximately 9 nm. Y2O3 particles were deposited on TiO2 terminated SrTiO3 (100) single-crystal substrates with areal densities up to 1654 particles µm−2 and subsequently covered with YBa2Cu3O7−δ by off-axis pulsed laser deposition (PLD). The areal density of the room temperature deposited particles is not changed by the substrate heating during PLD although their height on the substrate decreases. An influence on Jc is demonstrated for particle densities above 1588 particles µm−2, indicating that the substrate decoration with Y2O3 nanoparticles from the gas phase affects the formation of artificial pinning centres in the YBa2Cu3O7−δ films and can be applied to further study of the effect of particle size and areal density on defect formation in YBa2Cu3O7−δ.

An epitaxial Y2O3/YSZ/CeO2 buffer architecture has been prepared using pulsed laser deposition on cube texture Ni-3at.% W/Ni-10at.% Cr-1.5at.% Al and Ni-5at.% W/Ni-10at.% W composite tapes. The buffer layer growth was studied in detail and revealed good texture transfer throughout the structure, similar to standard Ni-5at.% W substrates. YBCO layers were successfully deposited on the buffered tapes and compared to films grown on SrTiO3 single crystals. A superconducting transition temperature of about 90K with a small transition width was observed on all metal substrates. A critical current density Jc of about 1MAcm -2 was measured at 77K in a self-field. It was found that J c is mainly limited by the grain boundary network in magnetic fields below 4T, whereas similar values as on SrTiO3 single crystals were measured at higher fields. � IOP Publishing Ltd.

The critical current density Jc is limited by the network of small angle grain boundaries in coated conductors based on biaxially textured metal substrates up to a texture dependent cross-over field. Below this cross-over field Jc can be improved by optimizing the grain boundary network. One possibility to enhance Jc at low magnetic fields is to use substrates with high aspect ratio grains. Therefore, cube textured Ni tapes micro-alloyed with silver were prepared having such an elongated grain structure with an aspect ratio of about 4. Highly textured NiO layers have been grown on these substrates using surface oxidation epitaxy (SOE). YBCO films were deposited afterwards on these substrates by pulsed laser deposition using a BaZrO3/SrRuO3 buffer layer architecture. Transport measurements revealed a significant enhanced Jc value along the rolling direction of the tape compared to the transverse direction. Similar results were obtained in numerical simulations based on measured EBSD texture maps.

A MgB2−xCx superconductor was prepared with reactive nanostructured carbon up to nominal x = 0.316 by high-energy ball milling. These products crystallize at temperatures below 700 °C, forming mainly MgB2−xCx with a particle size of about 20 nm and with lattice-dissolved carbon content up to about x = 0.13 under normal pressure conditions, and minor MgB4. The nominal higher addition of reactive nanostructured carbon does not have an influence on the a-axis of the MgB2−xCx structure. The superconducting behaviour reflects the optimum interplay of the lattice-dissolved carbon, which influences the carrier density, and the homogeneously distributed carbon, which probably acts as a pinning centre. For the sample with a nominal x = 0.221, the critical current density (Jc) increased by approximately one order of magnitude to Jc = 1.7 × 104 A cm−2 at 9 T and 4.2 K compared to the undoped MgB2.

Delaying nitrogen (N) applications into the growing season as a risk management tool is a concept that has received considerable attention in recent years. A 3-yr field study with spring wheat (Triticum aestivum L.) and canola (Brassica napus L.) was conducted at two Saskatchewan locations, Indian Head and Scott. The effects of postponing N applications for up to 30 d after seeding and several application methods were evaluated against mid-row banded urea at seeding. Liquid urea ammonium-nitrate (UAN) was applied at four separate times relative to seeding, either as an in-soil coulter band or a surface band. The surface band applications were applied either with or without the addition of 5% ammonium thiosulphate (ATS), a potential urease inhibitor. The dependent variables considered included plant density and grain yield for both crops, and grain protein in wheat. The only effect on plant density occurred in canola, where the post-seeding coulter applications slightly reduced stands compared with the other treatments. Postponing N fertilization for up to 30 d after seeding compared with N fertilization at seeding did not affect the yield of canola or protein in spring wheat, but reduced the yield of spring wheat at Indian Head in 2003, which was a very dry growing season. The coulter applications only showed a slight advantage over the surface band applications. For the surface band applications, the addition of 5% ATS did not provide a noticeable advantage over UAN alone. Canola appeared to be less sensitive to post-seeding applications than spring wheat. Deferring the entire amount of fertilizer N into the growing season appears to be a viable option but it is not without risk, especially when dry conditions are encountered. Key words: Triticum aestivum L., Brassica napus L., nitrogen management, no-till, surface dribble, urea-ammonium nitrate

A thin-film YBa2Cu3O7−δ sample has been investigated with regard to its irreversibility field at low temperatures. For these investigations, the magnetic-field dependence of the electrical resistance R(H) was measured at various temperatures in pulsed magnetic fields up to 50 T. These curves show an unusual, very rapid increase of R even at low fields. We describe a method of extracting Hirr that is comparable to measurements in static magnetic fields. The irreversibility line shows the same, nearly linear behaviour at low temperatures as bulk YBa2Cu3O7−δ samples and a power-law dependence at higher temperatures. These two regions are also clearly visible in pinning force plots.

An extensive study of the growth and properties of La 2 Zr 2 O 7 (LZO) buffer layers prepared by chemical solution deposition on Ni–5 at.%W rolling-assisted biaxially textured substrates, which is presently of great interest for the preparation of YBa 2 Cu 3 O 7− x -coated conductors, is presented. The main focus was on the understanding of the decomposition of the precursor layers, and their growth and texture formation, as well as their structural evolution during annealing, leading to highly biaxially textured LZO buffer layers. Therefore, various characterization methods, including spectroscopic analysis techniques, X-ray diffraction techniques, and other techniques, were applied. Epitaxially grown LZO buffer layers of high performance, showing a strong cube texture up to the surface, a crack-free surface morphology of low roughness, and a sufficient barrier function against Ni diffusion from the substrate, were reproducibly obtained.

Anharmonic contributions to the equation of state of solids are derived in closed form from a local mean-field potential for the atomic motion within the framework of the classical free-volume theory. The mean-field potential is calculated thereby from one cold isotherm and a series expansion of the partition function results in a good approximation for the anharmonic contribution up to the quartic terms. Quantum corrections are added to the classical terms to represent accurately experimental data for Cu, Ag, and Au.

An adequate buffer layer architecture is of great importance for YBa2Cu3O7?? (YBCO)-coated conductor fabrication. We present a transmission electron microscopy (TEM) analysis of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni?5?at.%W substrates for YBCO-coated conductors prepared by chemical solution deposition (CSD). The LZO thin films were heat-treated at 900 and 1050??C respectively. Electron diffraction patterns, and bright and dark-field images were used to determine the microstructure, texture and the nanoporosity of the films. By x-ray diffraction the films were found to be [100] oriented and strongly biaxially textured. Although x-ray diffraction suggests an epitaxial growth of LZO on Ni it was shown by TEM that this was not the case. The grain size of the films is between 100 and 300?nm and therefore much smaller than the Ni grain size of 40??m. Appropriate acquisition conditions for scanning electron microscopy (SEM) and TEM imaging are given to identify the nanogranularity of the films. For the film annealed at 1050??C high-resolution SEM images clearly show a polycrystalline LZO microstructure and the grain size can readily be determined. Electron diffraction rings are more pronounced than for the film annealed at 900??C, indicating a higher level of polycrystallinity in the film. SEM images of the film annealed at 900??C yield no evidence of a polycrystalline microstructure; only single misoriented LZO grains separated by 500?nm are observed. Nanovoids 10?40?nm in size were found in the LZO buffer layers with a high density. The voids had approximately cuboid shape, indicating an anisotropy of the surface energy in LZO. The surface planes of the voids were identified as {111} lattice planes. Despite the nanoporosity, which is a typical feature of CSD-grown buffer layers, the LZO buffer layers act as efficient Ni diffusion barriers. Energy dispersive x-ray microanalysis (EDX) in the transmission electron microscope yielded the composition of the films. In the LZO films no Ni-rich secondary phases were detected and significant C contamination occurred during spectrum acquisition.

At present, the development of superconducting YBa2Cu3O7−x coated conductors attracts much attention due to their enormous application potential in electric power systems. Worldwide research is focused on the investigation and improvement of buffer materials and YBa2Cu3O7−x superconducting properties as well as low-cost manufacturing processes in cooperation with industrial companies. Accordingly, chemical solution deposition has emerged as a highly competitive, versatile, and cost-effective technique for fabricating coated conductors of high performance. New chemical solution approaches are under development for buffer layer deposition. In order to achieve high critical current carrying YBa2Cu3O7−x layers, the established trifluoroacetate route is favored. This paper reviews the most recent work on chemical solution deposition within the IFW Dresden while also considering achievements on this specific research topic worldwide.

The behaviour of the upper critical field Hc2 of the multiphase magnetically ordering superconductor HoNi2B2C presents numerous features arising from the three distinct magnetically ordered phases of the material that form at temperatures below the superconducting critical temperature Tc, i.e. within the superconducting phase. A detailed investigation of the Hc2 of this material in the form of high-quality biaxially textured thin films has been conducted, including the only full set of angle-dependent measurements currently available. The results reveal a number of additional features that have hitherto been overlooked, in particular a far higher degree of anisotropy of the material throughout the entire temperature range below Tc than is commonly reported. By correlating these features with the known phase diagrams of the material, an explanation of the observed behaviour can be postulated, and the apparent loss of anisotropy attributed to the transition of the material into a different magnetic phase. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cube textured Cu/Cu-based tapes are shown to be an alternative to Ni/Ni alloy substrates widely used in high current capability YBCO-coated conductors. Copper, other than nickel, is non-magnetic and has a larger thermal and electrical conductivity, keeping up thermal stabilization of the superconductor at cryogenic temperatures. Jointly with the cube texture of exceptional strength that develops after rolling and recrystallization, Cu is, therefore, a candidate material for coated conductor architecture. In this work, we report on the texturing of pure copper and different copper alloys, such as Cu- Mn and a dispersion hardened Cu-B4C tape. For Cu and Cu-B4C, the maximum found in the cube texture histograms are 3.8° and 4.4°, respectively.

We present results of crack free layers of CeO2 and La2Zr2O7 deposited by means of CSD on cube textured Ni-4 at.% W substrates. EBSD-data show histograms with very good inplane- and out-of-plane textures and were used to simulate the critical current density in the YBCO layer. The surface roughness, a sensitive feature for good deposition results, was analyzed with a profilometer. In the CSD process we applied, the 2, 4-pentanedionates of the metal cations in glacial acetic acid and methanol served as starting substances.

To study the possibility of enhancing the pinning forces in YBa2Cu3O7?? films through the introduction of nanosized precipitates, quasi-multilayers of YBa2Cu3O7?? and a transition metal (TM = Ti,Zr,Hf) were deposited on single-crystal SrTiO3 substrates using pulsed laser deposition. The transition metal layer thickness was chosen to be less than one unit cell, resulting in separated nanoscale islands that form inclusions with perovskite structure BaTM O3 during film growth. These inclusions grow biaxially textured within the film. Whereas the Ti-doped films show a very strong decrease in the critical temperature Tc and, hence, a strong decrease in the critical current density Jc with increasing TM amount for all temperatures, Hf and Zr doping show an increase in Jc for the smallest amounts of doping. An irreversibility field as high as 10.3?T at 77?K was observed in the case of low Hf content.

The preparation and properties of Tl-2212 (Tl2Ba2CaCu2O8) thin films on biaxially textured Ni substrates, buffered with CeO2/YSZ/CeO2 trilayers, have been studied. Tl-2212 thin films were grown using a two-step fabrication process that involved magnetron sputtering and low temperature post-annealing. XRD θ–2θ scans, rocking curves and -scans proved that the Tl-2212 thin films were epitaxially grown on the buffered RABiTS. The critical temperature Tc and critical current Jc (77 K, 0 T) were 103 K and 2.6 MA cm−2, respectively.

Cube textured NiO layers were prepared by surface oxidation epitaxy on microalloyed Ni tapes. Different perovskite buffers were successfully grown on these substrates using pulsed laser deposition. Among them, BaZrO3 and SrZrO3 buffers show an excellent epitaxial growth on NiO with an in-plane orientation similar to the underlying NiO. The subsequent deposition of YBa2Cu3O7−x on top of these buffers requires a thin intermediate SrTiO3 layer and results in epitaxial layers with a Tc of about 89 K and Jc values up to 1.6 MA cm−2. Alternatively, epitaxial SrRuO3 was grown on NiO using a thin intermediate BaZrO3 layer leading to YBCO films of similar quality. The investigation of the magnetic field dependence of the critical current density shows the major influence of the grain boundary network in the low-field region.

Rare Earth-Transition Metal permanent magnet films were epitaxially grown by pulsed laser deposition on heated MgO single crystal substrates of different orientations. The epitaxial growth relation of film, buffer and substrate is studied by pole figure measurements and its consequences on the anisotropic magnetic behavior are discussed. In the investigated material systems, RCo 5 (R = Sm, Pr) and Nd-Fe-B, high anisotropies and coercivities are achieved, the film morphology, domain structure and the coercivity mechanism are, however, distinctly different. The small scaled domain structure found for SmCo 5 and PrCo 5 films is a consequence of the small grain sizes and the magnetization process is dominated by strong pinning. Nd 2 Fe 14 B based films, on the other hand, are nucleation type magnets and coercivity is influenced by film morphology and roughness.

In order to improve the extrinsic superconducting properties of MgB2 a combination of nanocrystalline microstructure and particle doping was studied with regard to the enhancement of flux pinning. For comparison, MgO and SiO2 particles were separately introduced into the MgB2 matrix by the in situ preparation technique of mechanical alloying. The oxides do not affect the formation of MgB2 but influence characteristically the critical current density Jc and the irreversibility field Hirr in hot pressed bulk samples due to a change of microstructure and lattice constants. Optimal doping levels are 5 wt.% for MgO and 2 wt.% for SiO2 addition, which lead to improved Jc values of 1.3 × 106 and 1.2 × 106 A/cm2 in self-field at 7.5 K, respectively, but do not affect the critical temperature Tc. Microstructural investigations revealed a nanocrystalline MgB2 matrix with homogeneously distributed impurity particles.

Thin MgO and TiN films have been grown using ion-beam assisted pulsed laser deposition on amorphous substrates. The texture development was analysed using an in situ reflection high-energy electron diffraction (RHEED). Above 250 °C, a sharp cube textured nucleation layer was observed in both materials using an ion beam with an energy of 800 eV under an angle of 45° relative to the substrate normal. The cube texture is not stable during further ion-beam assisted growth but could be preserved using homoepitaxial growth at higher temperatures. Resulting films revealed an out-of-plane orientation of about 6° and in-plane orientations of less than 13°. MgO and TiN showed close similarities in the texture development, i.e., the texturing was taken place within the first nanometres during nucleation. The observed texture development can be explained through a combination of overall energy minimization and anisotropic sputter rates. Highly textured YBCO layers were grown on these templates using additional buffer layers.

A reel-to-reel, dip coating process has been developed to continuously deposit epitaxial La2Zr2O7 (LZO) and CeO2 on 5 m long cube-textured {100} (001)Ni tapes. Recent results for La2Zr2O7 and CeO2 buffer layers deposited on long lengths of Ni substrate for the realization of YBa2Cu3O7−x (YBCO)-coated conductors are presented. The major achievement is the development of a new all chemical solution deposition (CSD) process leading to the formation of highly textured buffer layers at moderate annealing temperatures. Reproducible highly textured, dense and crack-free LZO buffer layers and CeO2 cap layers were obtained for annealing temperatures as low as 900 °C in a reducing atmosphere (Ar–5 at.%-H2). The thickness of the LZO buffer layers was determined to be (200 ± 10) nm per single coating; prepared cerium oxide layers showed a thickness of 60 nm ± 10 nm. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A Tc 0 of T = 90.5 K and ΔTc = 1.4 K was obtained on PLD-YBCO/CSD-CeO2 /CSD-LZO/Ni–5 at.% W, which shows the outstanding features of this new buffer layer architecture processed by CSD. The large layer thickness combined with low annealing temperatures is the main advantage of this new process for low-cost buffer layer deposition on Ni-RABiTS (rolling-assisted biaxially textured substrates).

The usual quasiharmonic Mie–Gruneisen (MG) equation of state is modified by the inclusion of ‘intrinsic anharmonicities’, which have been considered up to now primarily in the high temperature limit. A comparison with experimental data for the rare gas solids, Ar, Kr and Xe and for MgO reveals that the anharmonic contributions cannot be represented perfectly within the MG approximation. A small but significant modification of the MG approach is presented to estimate intrinsic anharmonic contributions within a mean-field approximation for the thermal part of the internal energy. This estimate results in reasonable interpolations to low temperatures, where quantum effects are dominant. The present approach is also compared with more restricted recent theoretical results.

A self-consistent statistical method for the calculation of thermodynamic properties for simple crystals is used to study the formation of vacancies in rare gas crystals (RGC) at high temperature near the melting point. We show that the vacancy formation energy drops dramatically as the melting temperature is approached and that the vacancies repel each other. An analysis of the solid state parameters at high temperature leads to the conclusion that at high temperature structural defects, such as vacancies, dislocations, etc., are centers of relaxation for the excessive potential energy of the interatomic interaction.

The preparation of cube textured NiO buffer layers on biaxially textured Ni tapes using surface oxidation epitaxy (SOE) offers a cheap and scalable route for the production of long-length YBCO coated conductors. A second buffer layer is necessary to ensure epitaxial growth of the YBCO as well as to prevent Ni contamination of the superconducting layer. Zirconate buffer layers offer a close lattice misfit to NiO as well as a high stability during the YBCO deposition. BaZrO/sub 3/ and SrZrO/sub 3/ buffers were successfully deposited on NiO using pulsed laser deposition. Additionally, BaZrO/sub 3/ films were prepared on NiO using metal-organic decomposition. All buffers show a high quality epitaxial growth with an in-plane orientation similar to the underlying NiO. The subsequent deposition of YBCO on top of these buffers resulted in epitaxial layers with a T/sub c/ above 85 K and j/sub c/ up to 1 MA/cm/sup 2/ on NiO if a thin intermediate SrTiO/sub 3/ layer is used. Microstructural investigations showed that the roughness and the surface topography of the buffer layers is mainly determined by the quality of the NiO layer.

The critical current density in RABiTS (rolling assisted biaxially textured substrates) based coated conductors is limited by the network of small-angle grain boundaries up to a texture dependent crossover field H/sub co/. The current flow through this network is percolative in nature and thus depends on misorientation angle distribution, the width and length of the tape, and on the grain shape. These dependencies were simulated using a fast and simple limiting path algorithm on real grain boundary networks obtained by electron backscattering diffraction (EBSD) and cross-checked with transport measurements. A strong dependence of J/sub c/ on conductor width below 20 grains and a large increase in J/sub c/ for elongated grains was found. H/sub co/ of tapes with very sharp cube textures are around 1 T at 77 K. Hence, the intra-grain pinning must be increased for a further improvement of coated conductors applied in higher magnetic fields. With transport measurements on YBa/sub 2/(Cu/sub 1-x/Zn/sub x/)/sub 3/O/sub 7-/spl delta// single crystalline thin films, the possibility of a J/sub c/ increase due to Zn doping was investigated. Monolayer films with Zn contents up to 0.2%, however, showed a decrease in J/sub c/ and H/sub irr/, whereas multilayer films with x=0.017% and x=0.025% Zn) showed an increase in J/sub c/ at 77 K.

X-ray diffraction measurements on diamond and various metals under hydrostatic pressures up to ∼140 GPa together with determinations of ruby luminescence line shifts provide new constraints for the refinement of a practical pressure scale based on either the ruby line shift or the X-ray diffraction with the given calibrants. Implications for other high-pressure studies with diamond anvil pressure cells as well as for theoretical high-pressure studies and for equation of state forms are discussed.

By using a simple single-pass reel-to-reel system, we demonstrate a simple and robust in-situ route for the continuous deposition of 1-2 m long Coated Conductors (CC) consisting of 1 /spl mu/m thick superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films deposited by thermal co-evaporation onto 100 nm thick CeO/sub 2/ buffered cube textured Ni tapes. The buffer layer was deposited by either e-beam or thermal evaporation using respectively ceria or metallic cerium. The structural and morphological properties of the samples were investigated by X-ray /spl thetav/-2/spl thetav/ Bragg-Brentano, and pole figure diffraction, Nomarsky optical microscopy and Scanning Electron Microscopy (SEM) analysis. The 123 composition was controlled during deposition by means of an atomic absorption system. The optimized buffer layer and YBCO layer are grown at 690/spl deg/C in respectively forming gas and oxygen partial pressures of 5/spl times/10/sup -5/ mbar. These conditions ensure the growth of dense and crack-free layers with good biaxial texture, as indicated by FWHM's values in the 5-7/spl deg/ range for both in- and out-of-plane orientations. Zero-resistance critical temperatures T/sub c/=86-87 K with transition widths /spl Delta/T/sub c/

Samples of cube textured Ni tapes were oxidized in flowing oxygen at different temperatures. Crystal orientation maps (COMs) of the resulting oxide layers were produced by electron backscatter diffraction. The oxide layers were also analysed by X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy (AFM). The oxide grain size of a sample oxidized at 600 degrees C was similar to that of the substrate and the oxide was highly textured, both indicating epitaxial growth. The orientation relationship between the substrate and the oxide was directly observed from XRD to be (111)NiO//(001)Ni, [101]NiO//[110]Ni with four, equivalent, in-plane variants. In each variant, the oxide has both110- and211-type directions parallel to the Ni110directions. Differences in oxide thickness and surface roughness on neighbouring grains were revealed by AFM and these were attributed to the existence of a range of oxide growth conditions resulting from small differences in the orientation of each substrate grain. Similar macrotexture and microstructure were observed on a sample oxidized at 1300 degrees C, but additional, facetted oxide crystals had formed at the oxide grain boundaries. COMs showed that these crystals were either cube or 45 degrees rotated cube orientated, a texture different to that of the large oxide grains. The grain boundary crystals were thought to form by inward diffusion of oxygen at defects in the growing oxide scale.

In order to improve the intrinsic properties of MgB2 superconductors, the application of mechanical alloying (MA) of elemental Mg and B powders is a very promising fabrication technique. The enhancement of the upper critical field Hc2 and the irreversibility field Hirr as well as of the critical current density Jc shows the potential of this preparation route. Nevertheless, a better understanding of the MA process would allow further optimization of its parameters for MgB2 preparation. The coaction of the grain refinement of the starting substances Mg and B with the chemical reaction forming MgB2 by mechanical fracturing, cold-welding and solid-state-reaction of the powder particles leads to a complex behaviour of the whole system. Additionally, the introduction of oxygen from the working atmosphere and the incorporation of W, C and Co impurities stemming from the milling tools has a strong influence. Hence, two opposed processes are taking place which lead?with the milling time as the only parameter?in the beginning to an improvement of the superconducting properties of MgB2. This can be attributed to the grain refinement resulting in a higher reactivity and, therefore, an optimal grain connectivity and a high density of grain boundaries in hot pressed nanocrystalline MgB2 bulks, which is due to clean surfaces and a larger surface area of the particles. In contrast, for milling times longer than 50?h this excellent performance degrades rapidly. The saturation of the grain refinement at a final coherent scattering length, which is regarded as a minimal bound for the grain size of about 10?nm associated with an enrichment of the impurities (mainly oxygen) to a maximum content of about 4.5?at% for the longest milling time, causes a porous microstructure with reduced grain connectivity. These results allow us to achieve an optimum MgB2 microstructure by applying appropriate mechanical alloying conditions, i.e.?a medium processing time of 50?h.

Cu- and Fe-cladded monofilamentary tapes and 19-filamentary tapes with Fe matrix have been prepared by the powder-in-tube (PIT) method using mechanically alloyed precursor powders consisting of the constituents Mg, B, and MgB2. Despite of the low Tc values of about 31 K for monofilamentary tapes with Fe sheath maximum critical current densities (Jc) of 29 and 6 kA/cm2 at 4.2 K in external magnetic fields of 7.5 and 10 T, respectively, were achieved. The maximum Jc value of 18.5 kA/cm2 at 20 K in a field of 2 T was obtained for these conductors. The heat treatment of the monofilamentary tapes under uniaxial pressure of 0.5 GPa led to enhanced Jc values compared to those of tapes annealed under normal pressure. Up to 27 and 11 kA/cm2 were achieved at 4.2 K in external fields of 8 and 10 T, respectively, for samples annealed under pressure. For the 19-filamentary tape Jc values up to 35 and 9 kA/cm2 in fields of 7.5 and 10 T, respectively, were measured at 4.2 K. Investigation of the microstructure by optical microscopy, SEM/WDX and XRD have shown that the high Jc values may be mainly due to the remarkably small grain size of the MgB2 phase and defects particularly precipitates of magnesium oxide. Jc of the Cu-cladded tapes is one order of magnitude below that of Fe-cladded ones. The main reason for this discrepancy is the higher porosity of the superconducting cores with Cu sheath compared to that with Fe sheath. At higher sintering temperatures strong interactions between the Cu sheath and constituents of the precursor contribute to the suppression of the superconducting properties of Cu-sheathed conductors.

The conductor width dependence of the critical current density Jc in the grain boundary network occurring in RABiTS based coated conductors is simulated using experimentally obtained electron backscattering diffraction (EBSD) maps and the exponential dependence of the critical current density on the misorientation angle. It is found that a conductor width of around 20 grains (of average size) is sufficient to pass 90% of the maximum current density, independent of texture quality and grain aspect ratio in the current direction. The aspect ratio does however influence the absolute value of Jc, giving higher Jc values for higher aspect ratios. These results are in good agreement with Jc simulations based on purely statistical grain boundary distributions.

It has been shown recently (Holzapfel et al 2001 J. Phys. Chem. Ref. Data 30 515-29) that equations of state (EOS) data for simple metals like Cu, Ag and Au can be described most accurately on the base of a modified Mie-Gruneisen model including intrinsic anharmonicities. In contrast to commonly applied parametric EOS forms, which use only temperature dependent parameters, V(T), K(T) and K'(T), in the same parametric form, the present approach describes the thermal pressure more accurately and allows therefore to extrapolate more safely into wider ranges of pressure and temperature. Starting from the phonon density of state and a separate modelling of zero temperature and thermal contributions including quasiharmonic and intrinsically anharmonic contributions, the low energy part of the phonon density of states is represented by a modified pseudo-Debye model, which needs only one additional Einstein frequency for the high energy part. This optimised model is successfully applied to describe not only the EOS of Cu, Ag and Au, but also of other simple solids like NaCl and MgO, which are of special interest for pressure measurements in wide ranges of pressure and temperature.

A statistical method is used to calculate thermodynamic properties of Ar, Kr and Xe (isobaric and isochoric heat capacity, bulk modulus, thermal expansion coefficient, interatomic distances, Gruneisen parameter), and good agreement with experimental values is observed. It is shown that at high temperature, slightly above the melting point of the rare gas crystals, an instability of the crystalline state occurs. As the temperature approaches this instability, the isobaric heat capacity and the thermal expansion coefficient show strong increases similar to the experimentally observed anomalies.

RECo 2 Laves phases with RE=Pr, Nd, Sm, Tb have been studied up to 40 GPa by energy dispersive X-ray diffraction. No structural phase transitions are observed for any of the compounds up to the highest pressures applied. The bulk modulus K 0 and its pressure derivative K 0 ′ for ambient conditions were determined for each compound. Data obtained with liquid N 2 as pressure transmitting medium could be fitted reasonably well with standard equations of state. However, pressure transmitting media like mineral oil and isooctane cause strong deviations from the regular hydrostatic behavior. This behavior can be explained by assuming relatively small values for the shear modulus ( G 0 K 0 ) for this class of materials making the RECo 2 Laves phases very sensitive to non-hydrostatic stress.

We present a noninvasive inductive analysis of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) IBAD (ion beam assisted deposition) and RABiTS (rolling assisted biaxial textured substrates) coated conductors that enable us to analyze the electromagnetic granularity effects. We distinguish flux penetration through grain boundaries and grains and determine the inductive intergranular critical current density. The signature of reverse flux at low angle grain boundaries has been clearly identified by the appearance of a peak in the return branch of the irreversible magnetization. The present analysis evidence that IBAD and RABiTS coated conductors may exhibit comparable inter-grain critical current densities with the determining factor being the average in-plane grain misorientation.

Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films were prepared via chemical solution deposition (CSD) in a trifluoroacetate (TFA) process. The dip coated substrates were treated in a two stage annealing process. We obtained epitaxially grown 190 nm thick films on single-crystalline strontium titanate with T/sub c/ of 89.9 K and a transition width of 0.7 K. Critical current densities up to 4 MA/cm/sup 2/ were reached. The interface between the substrate and the YBCO is sharp even on an atomic level. Biaxially textured strontium titanate films and ytterbium oxide films as buffer layers were also built in a TFA process on single-crystalline substrates. Biaxially textured CeO/sub 2/ buffer layers were deposited on nickel RABITS using a nonfluorine precursor.

Ni and Ni base alloys are good candidate substrate materials in the development of coated conductors. The present paper reports the development of a high strength (Ni–3%W/Ni–10%Cr–1.5%Al) composite tape of 80 μm thickness with strong cube texture.

The growth of nickel oxide (NiO) on {100}〈001〉 cube textured, rolling-assisted biaxially textured substrates (RABiTS) of pure nickel was studied. Single-phase (100) NiO formed only in a narrow temperature range at 1250 ± 5 °C. At lower or higher temperatures, other orientations, namely (111), (311), and (220), also formed. At 1250 °C, practically single phase (100) NiO was observed for short oxidation times t of 0.2–10 min (oxide thickness < 10 μm). For 10 < t < 120 min, small quantities of (111) NiO formed in addition to (100), but near-single-phase (100) NiO formed once again after oxidation for >150 min (thickness > 35 μm). The ratio of (100) to (111) textures with oxidation time is explained in terms of epitaxial constraints, growth rates, and oxygen absorption on the (100) and (111) grains. The optimum oxidation conditions are oxidation for approximately 0.5 min at 1250 °C in flowing oxygen, yielding (100) NiO, a few microns in thickness, and root-mean-square roughness of approximately 40 nm on the length-scale of the grain size.

A comparison of recent high pressure x-ray diffraction data for diamond and Ta with low pressure ultrasonic data provides a basis for the refinement of the ruby luminescence pressure scale, whereby not only the slope and curvature parameters A=1904 GPa and B=7.665 of the previous scale are changed, but evidence is given for a modified form for the ruby R1 luminescence line shift under pressure with A=1820 GPa, B=14, and an additional parameter C=7.3. This revised ruby pressure scale resolves to a large extent previous discrepancies between equation of state data derived from x-ray measurements on the basis of the currently used ruby scale, on the one hand, and ultrasonic or theoretical studies, on the other hand.

Instead of commercially available MgB2 powder, we have used partially reacted powder prepared by mechanical alloying. This precursor powder consists of grains with a size of only a few nanometres and contains reacted MgB2, and also the starting material Mg and B, and is, therefore, more reactive than fully reacted commercial powders. Using copper as a sheath material, tapes were prepared by the usual powder-in-tube process. After annealing at relatively low temperatures (770–870 K) in inert atmosphere, the tapes have good superconducting properties. Magnetically we have measured a critical current density of 400 kA cm−2 at 4.2 K.

Epitaxial thin films of the superconducting borocarbide compound YNi 2 B 2 C have been grown on single-crystal MgO (001) substrates using pulsed laser deposition. The deposition temperature has a strong influence on the structural properties of the films, which in turn affect the superconducting transition temperature, T c . The resulting phases and their orientations with respect to the substrate have been investigated by X-ray diffraction and HRTEM, using cross-section samples. For deposition temperatures around 750 °C, c -axis oriented growth of YNi 2 B 2 C films occurs preferentially. At lower temperatures a weaker a -axis orientation was found by X-ray diffraction, whereas by HRTEM grains with a -axis and a weak c -axis orientation could be identified. An interfacial layer some 100 nm thick was formed bordering on the substrate, comprising mainly Y 2 O 3 but also other epitaxially grown phases such as YNi 4 B. The growth directions of Y 2 O 3 are [001] at 750 °C and [111] at lower temperatures. The in-plane orientations and the lattice mismatches of the bordering phases were also investigated.

For the realization of a practical pressure scale based on equation of state (EOS) data for selected calibrants, a detailed modelling of the thermal contributions is required. While 'parametric EOS' forms with their temperature-dependent parameters V0 (T), K0 (T), and K'0 (T) are useful for limited ranges in pressure and temperature, the separate modelling of the zero-temperature and thermal contributions is more appropriate especially for wide temperature ranges under high pressures (Holzapfel W B, Hartwig M and Sievers W 2001 J. Phys. Chem. Ref. Data 30). The remaining uncertainties due to explicit anharmonic contributions beyond the implicit contributions of the quasiharmonic approximation are therefore discussed here in more detail.

Highly biaxially textured Ni tapes have been strengthened by introducing Al2O3 particles with internal oxidation. The tape strength could be increased by a factor of five compared to pure Ni tapes. Therefrom an engineering current density increase by a factor of 4 can be derived by reducing the substrate thickness. Al-oxide formation at the surface of the tapes is prevented by the design of a composite tape consisting of an Al free surface region and an Al containing core with about the same strength. In this composite Al2O3 only evolves in the tape core.

Hard magnetic SmCo films were prepared by pulsed laser deposition in UHV and at moderate background pressures on polycrystalline Al2O3. Structure and magnetic properties are discussed for varying Sm-content. The perpendicular anisotropy observed at a deposition pressure of 0.06 mbar is compared with texturing models known for sputtered samples.

Structural phase transitions in the TiH0.74 alloy have been studied in the pressure range extending to 30.5 GPa at temperatures of up to 630 K, using diamond anvils and energy dispersive x-ray diffraction. Two phase transitions were observed at high pressures. At room temperature, the TiH0.74 alloy undergoes a transition to the (η+ω) two-phase state at above 7 GPa, and then this state persists up to 30.5 GPa. The other phase transition occurs upon heating (η+ω)-TiH0.74 to T>560 K to give a single-phase state, ζ-TiH0.74. The ω-phase corresponds to the high-pressure phase of pure titanium. The Ti sublattices of the η- and ζ-phases are indexed within the tetragonal symmetry, their specific volumes being much the same. Analysis of the specific volumes and the hydrogen contents in these two phases suggests that hydrogen atoms are likely to occupy tetrahedral interstices in the ζ-phase and octahedral interstices in the η-phase.