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The dynamic properties of a ring-shaped superconducting magnetic bearing used in textile machines were studied for a micrometer displacement range. Therefore, a new measurement setup was designed that allows to excite the freely levitating magnet ring in a defined direction with small excitation amplitudes. Here, we focus on radial and axial excitations with amplitudes between 2 μm and 30 μm. The data were analyzed by a fast Fourier transformation approach. The resultant excitation response was fitted by the transfer function of a spring-mass-damper system under harmonic force excitation, which gives the stiffness and damping coefficient for the particular excitation direction. The analysis shows a minor stiffness increase with decreasing excitation amplitudes in radial as well as in axial direction. At the same time, no clear trend was found for the damping coefficient. In contrast to other bearing designs, the studied ring-shaped bearing exhibits a ratio of 3 between the axial and radial stiffness.

Superconducting levitation systems mainly use permanent magnetic tracks to generate the magnetic field required for levitation. However, switchable tracks are necessary for crossings or turnouts. We present flux density simulations, which show the applicability of a concept combining permanent magnets with electromagnets to realize such a switchable track segment. Both tracks were simulated together with a superconducting bulk in order to calculate and compare the levitation force of both track types. A similar levitation force was achieved by the simulation of the permanent magnetic track as for measurements of the same setup. Simulations of the zero-field cooling setup proved the concept and indicate how the different magnetic fields above both tracks influence the levitation force. Nevertheless, the levitation force reduction due to magnetic field difference is small enough to maintain stable levitation when transitioning from the permanent magnetic track to the switchable.

High critical current densities can be realized in high-temperature superconductors, such as YBa 2 Cu 3 O 7-δ (YBCO), by controlling the density, shape, size, and direction of a secondary phase. Whereas the dependence on the growth rate and deposition temperature has been widely studied as key parameters for nano-engineering the pinning landscape, the vicinal tilt of the substrate surface might have an additional influence. Therefore, we deposited 6 mol% BaHfO 3 (BHO)-doped YBCO on SrTiO 3 (STO) substrates with vicinal angles α between 0° and 40° to identify the influence of the tilt on the growth mode of BHO. An undisturbed epitaxial growth of the superconductor as well as an epitaxial integration of the BHO phase in the YBCO matrix is observed for all vicinal angles investigated. The critical temperature is constant up to α = 20°, whereas the self-field critical current density at 77 K starts to decrease above 10°. A detailed structural analysis of the film cross sections showed that the growth mode of BHO changes already for a vicinal tilt of 2° from a pure c-axis oriented growth to a layered structure with BHO aligned parallel to the YBCO ab-plane. We identified a strong influence of such a microstructure on the current flow in BHO-doped YBCO films on STO substrates as well as on MgO-based coated conductors prepared by inclined substrate deposition.

In the past years, different superconducting levitation systems were developed around the world. Most projects focused on optimizing the flux density in the working space of the superconductor in order to maximize the levitation force of the system. In general, these systems use tracks with permanent magnetic Halbach arrays or combine permanent magnets with steel yokes to maximize the usable flux density. Therefore, none of these tracks can easily be switched off to allow a safe crossing or to build a fast turnout switch without moving parts. A new track was designed containing permanent magnets and a YBCO-tape-coil to realize a fast switchable track. In this concept, the permanent magnets provide the flux used for levitation, whereas the coil controls the flux in the space above the track, where levitation usually takes place. The magnetic behavior of this new design was studied and improved with two-dimensional (2-D) and 3-D simulations. Afterwards, a demonstrator was built on which the induced magnetic field was measured in the different operation modes. The results of the measurements and the simulations indicate that the flux density above of the track might be controlled by the coil current. It was proven that the new track design generates magnetic fields comparable to the standard permanent magnetic track, whereas only residual fields are measured in inactive mode, which can be further reduced with negative coil currents.

In this paper we report on the structural and superconducting properties of an epitaxially grown Ba(Fe 1-x Ni x ) 2 As 2 thin film using pulsed laser deposition. As target we used an optimally Ni-doped single crystal prepared from self-flux. The superconducting transition temperature of 21.4 K is among the highest values reported for Ni doping exceeding the critical temperature of the single-crystal target. The upper critical field shows a very high slope, which is connected to two-dimensional effect. Transmission electron microscopy investigations indicate planar defects, which might be the origin of this behavior.

Epitaxial films are a useful tool to study the interplay between the microstructure and the electrocaloric properties in order to optimize the performance of these materials. Therefore, epitaxial 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) films were grown by pulsed laser deposition on (001)-oriented single crystalline SrTiO3 (STO) substrates using an epitaxial La0.7Sr0.3CoO3 buffer as bottom electrode and additional Au top electrodes on the surface of the PMN-PT layer. The main goal of our study was to characterize the influence of the laser fluence on the structural properties. Our data show that pyrochlore-free PMN-PT films can be realized for low fluences. The relative permittivity and the polarization were determined as a function of temperature to verify the ferroelectric quality of our films.

Thin films of Yb3 +/Er3 + codoped Pb(Zr,Ti)O3 (PZT:Yb/Er) have been epitaxially grown on the SrTiO3 buffered Si wafer by pulsed laser deposition. Strong upconversion photoluminescence was observed in the PZT:Yb/Er thin film. Using piezoresponse force microscopy, polar domains in the PZT:Yb/Er film can be reversibly switched with a phase change of 180°. Ferroelectric hysteresis loop shape with a well-saturated response was observed. The epitaxially grown lanthanide-doped PZT on silicon opens up a promising route to the integration of luminescent functional oxides on the silicon platform.

Pure and 6 mol% BaHfO3 (BHO)-doped $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ (YBCO) films with a film thickness of around 1 $\mu\text{m}$ were prepared on CeO2-buffered ABAD-YSZ templates by pulsed laser deposition. The self-field $J_{\mathrm{c}}$ at 77 K reaches 1.1 MA/cm2 in the doped sample compared with 2.5 MA/cm2 in pure YBCO. Above a magnetic field of 2.2 T along $B\|c$ , $J_{\mathrm{c}}$ of the BHO-doped sample exceeds the $J_{\mathrm{c}}$ of the undoped film. The maximum pinning force density $(F_{\mathrm{P},\max})$ reaches a value of around 3 GN/cm2 for both samples, but $B(F_{\mathrm{P},\max})$ increases from 1.4 T (pure) to a value of 2.9 T (BHO:YBCO). The $J_{\mathrm{c}}$ anisotropy curves of the doped sample show a large and broad peak at $B\|c$ and a strongly reduced anisotropy at all temperatures and fields compared with the pure sample. A complex defect structure with YBa2Cu4O8 intergrowths, Y2O3 precipitates, and BHO nanocolumns with a fan-shaped structure is observed by transmission electron microscopy investigations, which can explain the measured $J_{\mathrm{c}}(B,\theta)$ behavior.

A new approach for the deposition of layers for coated conductors has been developed. High-frequency surface acoustic waves (SAWs) were applied for the atomization of precursor solutions into an ultrafine aerosol. The deposition via aerosol droplet condensation offers several advantages over existing deposition methods including ink jet printing and dip coating, e.g., a variable droplet size and the possibility of gel condensation in the aerosol phase due to solvent evaporation. In the future, a combination of two or more SAW atomizers might enable the simultaneous deposition of separate solutions and even nanoparticle dispersions. First, experiments were performed using water-based and propionic-acid-based mixed lanthanum and zirconium precursor solutions. These solutions are supplied to a SAW device via a stainless steel capillary, leading to continuous aerosol production. The aerosol droplets of the precursor solution were deposited on biaxial textured Ni-5 at.%W tapes having an area of 1-cm width and about 5-cm length and were subsequently crystallized into a continuous thin La 2 Zr 2 O 7 buffer layer in a tube furnace. X-ray diffraction studies showed that the La 2 Zr 2 O 7 films have high crystalline quality with a strong (001)-orientation. Furthermore, microstructural analysis on the deposited films showed homogeneous and dense layers.

The critical current I c (B) of YBa 2 Cu 3 O 7-δ (YBCO) coated conductors can be increased by growing thicker superconductor layers as well as improving the critical current density J c (B) by the incorporation of artificial pinning centers. We studied the properties of pulsed laser deposited BaHfO 3 (BHO)doped YBCO films with thicknesses of up to 5 μm on buffered rolling-assisted biaxially textured Ni-5 at% W tape and alternating beam assisted deposition textured Yttrium-stabilized ZrO 2 layers on stainless steel. X-Ray diffraction confirms the epitaxial growth of the superconductor on the buffered metallic template. BHO additions reduce the film porosity and lower the probability to grow misoriented grains, hence preventing the J c decrease observed in undoped YBCO films with thicknesses >2 μm. Thereby, a continuous increase in I c at 77 K is achieved. A mixed structure of secondary phase nanorods and platelets with different orientations increases J c (B) in the full angular range and simultaneously lowers the J c anisotropy compared to pristine YBCO.

Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT) is one of the most promising ferroelectric material for actuator, dielectric and electrocaloric applications. However, oriented and phase pure thin films are essential to use the outstanding properties of these compounds. In this work it is demonstrated that the use of miscut substrates influences the growth mechanism leading to a significantly broader deposition window to achieve the required film quality. Therefore, epitaxial 0.68Pb(Mg 1/3 Nb 2/3 )O 3 –0.32PbTiO 3 films were grown by pulsed laser deposition on (001)-oriented single crystalline SrTiO 3 (STO) substrates with a miscut angle between 0 and 15° towards the [100] direction using a conducting La 0.7 Sr 0.3 CoO 3 buffer layer. The influence of the vicinal angle on the PMN–PT structure was studied by high resolution X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. A nearly pure perovskite phase growth with a cube-on-cube epitaxial relationship was obtained on all miscut STO substrates, whereas a significant volume fraction of the pyrochlore phase was present on the standard substrate. Reciprocal space measurements revealed a peak split of the perovskite reflections indicating structural variants of PMN–PT with different c / a ratios. An additional tilting of the PMN–PT planes with respect to the buffer layer was observed on some samples, which might be explained with the incorporation of dislocations according to the Nagai model. Polarization loops were measured in a temperature range between room temperature and 150 °C showing a sharp drop of the remanent polarization above 65 °C on vicinal substrates.

$\hbox{La}_{{\kern-.5pt}1{\kern-.5pt}.{\kern-.5pt}85}{\kern-.5pt}\hbox{Sr}_{{\kern-.5pt} 0{\kern-.5pt}.{\kern-.5pt}15}{\kern-.5pt}\hbox{CuO}_{{\kern-.5pt}4}$ , $\hbox{BaFe}_{{\kern-.5pt}1{\kern-.5pt}.{\kern-.5pt}8}{\kern-.5pt}\hbox{Co}_{{\kern-.5pt} 0{\kern-.5pt}.{\kern-.5pt}2}{\kern-.5pt}\hbox{As}_{{\kern-.5pt}2}$ and $\hbox{FeSe}_{{\kern-.5pt}0{\kern-.5pt}.{\kern-.5pt}5}{\kern-.5pt}\hbox{Te}_{{\kern-.5pt}0.5}$ thin films have been prepared on piezoelectric (001) $\hbox{Pb}(\hbox{Mg}_{1/3}\hbox{Nb}_{2/3})_{0.72}\hbox{Ti}_{0.28}\hbox{O}_{3}$ substrates. By the use of the inverse piezoelectric effect, biaxial strain was induced into the films by applying an electric field to the sample. The strain sensitivity of the upper critical field and of the irreversibility line was determined by the analysis of the resistive transition. A biaxial compression in the order of 0.02% results in a shift of these fields. A consistent description of the field dependence is possible taking into account a strain dependent transition temperature. No influence of the strain state on the anisotropy of the upper critical field was found in first approximation.

YBa 2 Cu 3 O 7-δ (YBCO) films with a thickness of up to 2 μm containing nano-sized BaHfO 3 (BHO) have been grown on biaxially textured metal tapes by pulsed laser deposition. Transmission electron microscopy revealed the inclusion of Y 2 O 3 platelets and rod-like BHO structures. A c-axis oriented growth of the YBCO layer and biaxial oriented incorporation of BHO is confirmed by X-Ray diffraction. BHO expands the c-axis of YBCO, flattens the surface of YBCO and densifies the films. Y 2 O 3 inclusions get smaller and finer distributed, possibly with a positive influence on pinning effects. A superconducting transition temperature T c of about 89 K was determined, decreasing slightly with increasing BHO content. Transport current measurements in the maximum Lorentz force configuration showed an increased irreversibility field H irr and higher pinning force density F p with increasing BHO content in high magnetic fields.

The current transport capability of YBa 2 Cu 3 O 7-x (YBCO) based coated conductors (CCs) is mainly limited by two features: the grain boundaries of the used textured template, which are transferred into the superconducting film through the buffer layers, and the ability to pin magnetic flux lines by incorporation of defined defects in the crystal lattice. By adjusting the deposition conditions, it is possible to tailor the pinning landscape in doped YBCO in order to meet specific working conditions (T, B) for CC applications. To study these effects, we deposited YBCO layers with a thickness of about 1-2 μm using pulsed laser deposition on buffered rolling-assisted biaxially textured Ni-W substrates as well as on metal tapes having either an ion-beam-textured YSZ buffer or an MgO layer textured by inclined substrate deposition. BaHfO 3 and the mixed double-perovskite Ba 2 Y(Nb/Ta)O 6 were incorporated as artificial pinning centers in these YBCO layers. X-ray diffraction confirmed the epitaxial growth of the superconductor on these templates as well as the biaxially oriented incorporation of the secondary phase additions in the YBCO matrix. A critical current density J c of more than 2 MA/cm 2 was achieved at 77 K in self-field for 1-2 μm thick films. Detailed TEM (transmission electron microscopy) studies revealed that the structure of the secondary phase can be tuned, forming c-axis aligned nanocolumns, ab-oriented platelets, or a combination of both. Transport measurements show that the J c anisotropy in magnetic fields is reduced by doping and the peak in the J c (θ) curves can be correlated to the microstructural features.

Rotating superconducting bearings promise great potential in applications due to their frictionless operation. However, these bearings show a lower dynamic stiffness and damping coefficient compared to ball bearings. In this paper we studied a bearing consisting of a fixed YBCO ring and a rotating magnet above the superconductor. The influence of the magnet aspect ratio on the dynamic stiffness of the bearing was investigated in order to find an optimized size. To change the aspect ratio, we kept the inner diameter of the ring constant and reduced the outer diameter while increasing the ring height. In addition to these magnets, one magnet with a reduced cross-sectional area was studied. The aspect ratio selection was based on preliminary magnetic flux density simulations, which compared the magnetic flux density distribution and the potential radial force for different aspect ratios. To conduct the measurements, the field-cooled magnets were displaced in a lateral direction and then released, resulting in a damped oscillation. The dynamic stiffness constants were calculated for each bearing from the relation of three axis acceleration measurements for different field cooling heights. The comparison of the stiffness constants for the different bearings revealed an optimal aspect ratio for the given YBCO ring. This optimum is almost independent from the cooling height. The comparison between the two magnet rings with similar diameters and different heights was similar for the bearing characteristics at a low cooling height, whereas a significant reduction of stiffness was observed with a larger cooling distance. The difference is bigger for the magnet with a reduced height. The optimal aspect ratio as well as the stiffness dependence on the cross-sectional area was confirmed by simulations of the magnetic flux density distribution.

In this work we present multilayers consisting of Fe and Co-doped BaFe 2 As 2 fabricated by UHV pulsed laser deposition. Employing the advantage of a coherent interfacial bonding between the FeAs tetrahedra of the iron pnictide and bcc Fe enables the growth of epitaxial bi- and multilayers of Fe and the new Fe-based superconductors with high crystalline quality. Epitaxial growth of the multilayers was controlled in situ by reflection high energy electron diffraction (RHEED) and after film growth by X-ray diffraction and TEM analysis. The stoichiometry determined by Auger electron spectroscopy (AES) indicated As-deficient layers of Co-doped Ba-122. The multilayers exhibit critical temperatures of T c,90 = 29 K which is so far the highest critical temperature reported for Co-doped Ba-122. We propose that the T c -enhancement is caused by As-vacancies.

The incorporation of nanoscaled pinning centers in superconducting YBa 2 Cu 3 O 7-δ (YBCO) films is one of the core topics to enhance the critical current density J c (B, Θ) of coated conductors. The mixed double-perovskite Ba 2 Y(Nb/Ta)O 6 (BYNTO) can be grown in nanosized columns parallel to the YBCO c-axis and in steplike patterns, making it customizable to meet specific working conditions (T, B, Θ). We compare a 1.6 μm thick film of pure YBCO and a similar film with additional 5 mol% of BYNTO, grown by pulsed laser deposition with a growth rate of 1.6 nm/s on chemically buffered biaxially textured Ni-5at.% W tape. Our doped sample shows nanosized BYNTO columns parallel to c YBCO and plates in the ab-plane containing Y, Nb, and Ta. An improved homogeneity of the critical current density J c over the sample was evaluated from trapped field profiles measured with a scanning Hall probe microscope. The mean J c in the rolling direction of the tape is 1.8 MA/cm 2 (77 K, self-field) and doubles the value of the undoped sample. Angular-dependent measurements of the critical current density, J c (Θ), show a decreased anisotropy of the doped film for various magnetic fields at 77 K and 64 K.

GdBa 2 Cu 3 O 7-x (GdBCO) films doped with up to 13.6 mol.% BaHfO 3 (BHO) have been grown by electron beam physical vapor deposition (EB-PVD). A critical current density J c at 30 K, 3 T of 2.34 MA/cm 2 has been achieved for a doping level of 10.6 mol.%. This is the first report of artificial pinning centers being successfully incorporated into REBa 2 Cu 3 O 7-x (REBCO, RE = Y, Gd, Dy . . .) via EB-PVD. The samples were grown on Hastelloy tapes coated with a MgO buffer layer deposited by inclined substrate deposition. The J c of the samples was characterized at 77 K, 1 T and at 30 K, 3 T. An increase in J c (30 K, 3 T) upon Hf addition has been observed in the whole angular range α. The level of Hf addition was found to heavily influence the kind of nanoprecipitate formed, with low levels of Hf causing a reduction in the anisotropy of J c (77 K, 1 T) and higher levels of Hf resulting in the formation of nanoprecipitates elongated parallel to the GdBCO ab-plane, causing an increase in the anisotropy of J c (77 K, 1 T). The largest J c (77 K, sf) measured was 0.63 MA/cm -2 .

Scanning electron microscope imaging and electron backscatter diffraction are applied to 400 nm thick YBCO films grown on Ni-9at.%W and ABAD-YSZ tape. On Ni-9at.%W tape, the orientation of YBCO strongly varies from grain to grain, which is attributed to the different orientations of the underlying substrate grains with regard to the surface normal. On ABAD-YSZ, the structures causing the orientation variations are observed on a micrometer scale only, which is attributed to the granularity of the template. In contrast to Ni-9at.%W where no preferred misorientation axis is notable within single substrate grains, the misorientation of YBCO on the ABAD-YSZ tape is primarily caused by lattice rotations about the sample normal.

Ion-beam assisted deposition (IBAD) is one of the major approaches to realise highly textured templates for YBa 2 Cu 3 O 7− x (YBCO) coated conductors. Whereas IBAD-MgO is mostly used so far in such buffer architectures, TiN is a suitable alternative for this approach as it is showing a similar textured nucleation required for fast processing. Highly textured TiN films were prepared by ion beam assisted pulsed laser deposition on Hastelloy as well as on stainless steel using a Ta 0.75 Ni 0.25 or Y 2 O 3 bed layer. The biaxial texture was preserved to a higher thickness using homoepitaxial growth at higher temperatures and transferred to a second SrZrO 3 buffer layer. Finally, YBCO layers with an in-plane and out-of-plane alignment of less than 6° and 3°, respectively, were prepared on the buffered metal tapes leading to critical current densities well above 1 MA/cm 2 . The microstructure of the different architectures was studied in detail.

Ion Beam Assisted Deposition (IBAD) offers the opportunity to prepare highly textured templates for YBa2Cu3O7-δ (YBCO) coated conductors. We investigated a new simplified buffer layer architecture on mechanically polished stainless steel tapes with an amorphous Ta0.75Ni0.25 bed layer. Cube textured TiN layers have been prepared by ion beam assisted pulsed laser deposition on these substrates. Consequently, highly textured YBCO layers were obtained with an (103) in-plane alignment of Δφ = 5.9° using an additional SrZrO3 buffer layer. A maximum critical current density of about 2.9 MA/cm2 was measured at 77 K in self-field. The films showed an improved Jc(H)-behavior compared to standard YBCO coated conductors.

Pulsed laser deposition was used in combination with real time reflection high energy electron diffraction to prepare layer-by-layer grown La 1 − x Sr x CoO 3 films on single terminated substrates. The films exhibit an epitaxially and completely strained film growth resulting in an atomic flat surface with terrace structure. The films were compared to similar layers grown by off-axis laser deposition under higher oxygen partial pressure. With decreasing oxygen pressure an increased unit cell volume and decreasing magnetic moment was observed. Furthermore, we exemplarily show the preparation of layer-by-layer grown LaCoO 3 |SrTiO 3 multilayers.

Through dip-coating Ni-5%W substrates in a water-based sol-gel solution, thin films of La2Zr2O7 (LZO) were produced. This method yields highly crystalline and epitaxial films. The surface of the LZO film was found to be smooth and homogeneous. Subsequently, CeO2 layers followed by an YBa2Cu3O7-y layer were deposited via Pulsed Laser Deposition (PLD) onto the LZO film. The crystallinity and biaxial texture of the LZO layer was successfully transferred to the next layers, as demonstrated by pole figures and RHEED measurements. Resistive Tc-measurements were carried out on these samples and showed a Tc of 85 K.

Ion beam assisted deposition (IBAD) was used in combination with pulsed laser deposition to develop a conductive biaxially textured buffer architecture based on IBAD-TiN for coated conductor applications. Highly textured TiN layers were prepared on Hastelloy substrates with an amorphous Y2O3 seed layer. The cube textured nucleation layer was preserved to higher thicknesses using homoepitaxial growth. A double layer of Au and Ir was used to reduce the lattice misfit between TiN and YBCO. Finally, a 120 nm thick Nb:SrTiO3 layer was deposited to ensure the epitaxial growth of the superconducting YBCO layer at higher oxygen pressures. In-situ RHEED measurements revealed an undisturbed epitaxial growth of the complete buffer layer stack. The buffered tape was successfully used for the deposition of a 300 nm thick YBa2Cu3O7-x layer, showing an in-plane FWHM value of 7.2deg and a critical temperature T c of about 88 K. The results are promising for the development of a completely electrical conductive buffer architecture based on the IBAD approach.

In the present work, La 2 Zr 2 O 7 (LZO) buffer layers were deposited using pulsed laser deposition (PLD) on various metallic substrates including epitaxial pure Ni on a LaAlO 3 (LAO) substrate as well as highly textured Ni–5 at.%W tapes. It is shown that the LZO deposited on pure Ni-buffered LAO exhibits a mixed orientation while LZO on Ni–5 at.%W grows epitaxially. This difference may be explained by the existence of a sulphur superstructure on the surface of Ni–5 at.%W tapes, promoting the epitaxial (0 0 l ) nucleation of seed layers. Highly textured YBa 2 Cu 3 O 7− δ layers were prepared either by using a single buffer layer of LZO or bilayer buffers of CeO 2 /LZO on Ni–5 at.%W. The superconducting transition temperature ( T c ) increases with the LZO thickness, reaching a value of 90 K with a very narrow transition width (1.5 K) for 240 nm thick LZO layers. Inductive J c measurements at 77 K in self-field show a value of about 0.96 MA/cm 2 for the thickest LZO layers, which is comparable to the value observed on standard buffer architectures such as CeO 2 /YSZ/Y 2 O 3 .

Thin films of La2Zr2O7 (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.

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 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.

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.

In this work, the chemical and microstructural stability of YBiO3 buffer layers during the growth of YBa2Cu3O7-delta (YBCO) was studied. The superconducting YBCO films were deposited via both Pulsed Laser Deposition as well as Chemical Solution Deposition. Although excellent superconducting properties are obtained in both cases, self-field critical current densities of 3.6 and 1.2 MA/cm(2) respectively, chemical instability of the YBiO3 buffer layer is observed. An elaborate transmission electron microscopy study showed that in the case of vacuum deposited YBCO, the YBiO3 becomes unstable and Bi2O3 sublimates out of the architecture. Due to this structural instability, an intermediate Y2O3 layer is obtained which maintains it microstructural orientation relation with the substrate and acts as growth template for YBCO. For chemical solution deposited YBCO, reaction of YBCO with the YBiO3 buffer layer is observed, leading to large grains of YBa2BiO6 which are pushed towards the surface of the films and strongly reduce the superconducting properties. Upon using high growth temperatures for the superconducting layer, these secondary phases decompose, which subsequently leads to Bi2O3 sublimation and a textured YBCO film which directly nucleated onto the LaAlO3 single crystal substrate. Hence, this electron microscopy study indicates that bismuth-based buffer layers systems are not suitable for implementation in coated conductors. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Biaxially textured La2Zr2O7 (LZO) and Ce–Gd–O (CGO) buffer layers were grown on Ni-RABiTS (rolling-assisted biaxially textured substrates) to obtain suitable buffer layer architectures for YBa2Cu3O7−x (YBCO) coated conductors. Both buffer systems were prepared using newly developed precursor solutions containing a simple carboxylic acid as solvent. Reproducible highly textured LZO buffer layers were obtained at annealing temperatures as low as 900 °C. CGO buffer layers were grown on top of LZO at annealing temperatures of 1000 °C. Both layers revealed a very good in-plane alignment and are textured up to the surfaces. These results, obtained using new precursor solutions, which are simple in preparation, are very promising for further development of low cost buffer layer architectures for YBCO coated conductors.

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.

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.

High temperature oxidation of cube textured (1 0 0)Ni and (1 0 0)Ni–0.1wt%(Mo or Mn) was carried out in a wide temperature regime between 900 and 1400 °C in air. Special attention was paid to avoid pre-oxidation at lower temperatures, thus favouring nucleation controlled surface oxidation epitaxy (SOE) as opposed to SOE achieved by competitive grain growth. Consequently, cube textured epitaxial NiO layers, under 1 μm in thickness, have been grown on pure Ni in a much wider working window than previously published. Furthermore, thin cube textured NiO layers have been grown on Ni–0.1%Mo tape in a still wider working window of ∼200 °C between 1150 and 1350 °C. Preliminary results on Ni–0.1wt%Mn show a similar trend. An in-plane orientation of

We report on the transport properties of clean, epitaxial Fe(Se,Te) thin films prepared on Fe-buffered MgO (001) single crystalline substrates by pulsed laser deposition. Near Tc a steep slope of the upper critical field for H||ab was observed (74.1 T/K), leading to a very short out-of-plane coherence length, \xi c, of 0.2 nm, yielding 2\xi c(0) approximately 0.4 nm. This value is shorter than the interlayer distance (0.605 nm) between Fe-Se(Te) planes, indicative of modulation of the superconducting order parameter along the c-axis. An inverse correlation between the power law exponent N of the electric field-current density (E-J) curve and the critical current density, Jc, has been observed at 4 K, when the orientation of H was close to the ab-plane. These results prove the presence of intrinsic pinning in Fe(Se,Te). A successful scaling of the angular dependent Jc and the corresponding exponent N can be realized by the anisotropic Ginzburg Landau approach with appropriate \Gamma values 2~3.5. The temperature dependence of \Gamma behaves almost identically to that of the penetration depth anisotropy., Comment: 8 figures

Epitaxial BaZr x Ti1−x O3 (BZTO) thin films with Zr contents of x = 0, x = 0.12 and x = 0.2 were grown by pulsed laser deposition on (0 0 1)-oriented single crystalline SrTiO3 substrates utilizing an additional conducting SrRuO3 buffer layer. It was found that the oxygen pressure during the deposition heavily influences the lattice constants and the microstructure of BZTO. A low of 0.01 mbar gives rise to a significant tetragonal distortion. Texture measurements reveal that an undisturbed epitaxial growth is only achieved for BZTO films prepared in 0.01 mbar oxygen. In contrast, the formation of twins was observed for higher . A detailed microstructural analysis indicates that the sample preparation in low prevents a preferential growth of columnar grains within the BZTO layers and leads to smoother film surfaces. BZTO thin films deposited with optimized deposition parameters show characteristic ferroelectric polarization behavior. The saturation polarization at room temperature declines with increasing Zr content and the characteristic ferroelectric hysteresis diminishes. Temperature-depended measurements of the relative permittivity reveal the existence of a broad transition range and a significant shift of the phase transition temperature to lower values for increasing Zr content.

Biaxially textured MgO films have been grown using ion-beam assisted pulsed laser deposition. Above 250 °C a cube texture with a 〈1 1 0〉 direction parallel to the ion beam is observed in films thinner than 10 nm at ion incidence angles between 35° and 55°. The in-plane alignment determined using RHEED analysis was better than 21°. A strongly anisotropic sputter rate is responsible for this oriented nucleation. During further growth the nucleation texture changes in such a way that the 〈1 0 0〉 direction becomes parallel to the ion beam. This change can also be explained by the anisotropic sputter rate of MgO found in sputtering experiments on single crystals selecting grains with a 〈1 0 0〉 direction parallel to the ion beam during growth.

In this work, water-based precursor solutions suitable for dip-coating of thick La{sub 2}Zr{sub 2}O{sub 7} (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100-280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55{sup o}. TEM studies illustrated the presence of nanovoids, typical for CSD-LZO films annealed under Ar-5%H{sub 2} gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer. - Graphical abstract: Thick LZO buffer layers from water-based precursor solutions were synthesized and their crystallinity, microstructure and buffer layer action were studied. The buffer layer action of the LZO layer was substantial to restrict the Ni penetration within 30 nm of a 140 nm thickmore » film. Highlights: > LZO buffer layers with high thicknesses for use in coated conductors were prepared. > Prepared from water-based solutions. > Polymeric PVP increases the crack-free critical thickness of thick films. > Thick films showed good barrier action against Ni penetration. > Seed layers promote epitaxial growth of thick layers.« less

The angular-dependent critical current density, ${J}_{\text{c}}(\ensuremath{\Theta})$, and the upper critical field, ${H}_{\text{c}2}(\ensuremath{\Theta})$, of epitaxial $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}$ thin films have been investigated. No ${J}_{\text{c}}(\ensuremath{\Theta})$ peaks for $H\ensuremath{\parallel}c$ were observed regardless of temperatures and magnetic fields. In contrast, ${J}_{\text{c}}(\ensuremath{\Theta})$ showed a broad maximum at $\ensuremath{\Theta}=90\ifmmode^\circ\else\textdegree\fi{}$, which arises from intrinsic pinning. All data except at $\ensuremath{\Theta}=90\ifmmode^\circ\else\textdegree\fi{}$ can be scaled by the Blatter plot. ${H}_{\text{c}2}(\ensuremath{\Theta})$ near ${T}_{\text{c}}$ follows the anisotropic Ginzburg-Landau expression. The mass anisotropy increased from 1.5 to 2 with increasing temperature, which is an evidence for multiband superconductivity.

Epitaxial hcp cobalt films with pronounced $c$-axis texture have been prepared by pulsed lased deposition either directly onto ${\text{Al}}_{2}{\text{O}}_{3}(0001)$ single-crystal substrates or with an intermediate ruthenium buffer layer. The crystal structure and epitaxial growth relation was studied by x-ray diffraction, pole figure measurements, and reciprocal-space mapping. Detailed vibrating-sample magnetometer analysis shows that the perpendicular anisotropy of these highly textured Co films reaches the magnetocrystalline anisotropy of hcp-Co single-crystal material. Films were prepared with thickness $t$ of $20ltl100\text{ }\text{nm}$ to study the crossover from in-plane magnetization to out-of-plane magnetization in detail. The analysis of the periodic domain pattern observed by magnetic force microscopy allows us to determine the critical minimum thickness below which the domains adopt a pure in-plane orientation. Above the critical thickness the width of the stripe domains is evaluated as a function of the film thickness and compared with domain theory. Especially the discrepancies at smallest film thicknesses show that the system is in an intermediate state between in-plane and out-of-plane domains, which is not described by existing analytical domain models.

The strength of the unidirectional, uniaxial, cubic, and dynamic rotatable anisotropy field together with the effective damping parameter in polycrystalline ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}∕\mathrm{Ni}\mathrm{O}$ ferromagnet and/or antiferromagnet systems is studied as a function of NiO thickness and thermal history. A partial transformation of antiferromagnetically induced combined uniaxial and cubic anisotropy to undirectional anisotropy with increasing NiO thickness is confirmed by hysteresis loop modeling. Independent of the occurrence of exchange bias, the overall exchange anisotropy is constant over a wide range of NiO thickness. A reduction of exchange bias with initial annealing is due to a transformation from a fixed to a rotatable antiferromagnetic spin structure, manifesting itself in the appearance of rotatable anisotropy. With annealing at the interface a ${\mathrm{Ni}}_{x}{\mathrm{Fe}}_{y}{\mathrm{O}}_{z}$ layer is formed that changes the interfacial coupling, leading to an additionally enhanced rotatable anisotropy and spin-wave damping. The data imply that the spin structure inside the antiferromagnetic layer is responsible for exchange bias and the dominating contribution to coercivity, the interfacial structure for the overall coupling. The chemical interface structure and the thermomagnetic history are relevant, and have to be taken into account, comparing experimental data with theoretical models of exchange coupling.

Recently large attention has been devoted to chemical solution deposition (CSD) as a promising method for fabricating low-cost YBCO coated conductors. We present an extensive transmission electron microscopy (TEM) cross-section analysis of CSD grown La 2 Zr 2 O 7 (LZO) buffer layers on flexible Ni–5at%W substrates. The high performance of these chemical solution derived buffer layers was confirmed by a YBCO critical current density J c of 0.84 MA/cm 2 achieved for a coated conductor sample with a layer sequence Ni–5at%W/LZO (CSD)/CeO 2 (CSD)/YBCO, where the YBCO film was deposited by pulsed laser deposition (PLD). TEM sample preparation was carried out by conventional mechanical polishing and ion milling techniques. TEM bright-field images of the LZO films and nickel substrates were acquired under two-beam conditions. The layer thicknesses and nanovoid size were determined for the LZO buffer layers. Moreover, the interfaces between the different layers were investigated and identified. Electron diffraction patterns were obtained in order to determine the microscopic texture of the samples. Despite the presence of nanovoids in the LZO buffer layers, they act as efficient Ni diffusion barriers.

Quasi-multilayers of Y123/M (M = incomplete oxide layer) are prepared by using pulsed laser deposition. X-ray diffractions indicate that the different growth-controlled precipitates occur inside base films of Y123. In the case of M = YSZ, a heterogenous perovskite phase of BaZrO 3 , forms as the result of a solid state reaction of YSZ with Y123, leading to T c obviously decreasing with increasing of M. In the case of M = Y 2 O 3 , however, T c does not decrease so much. Magneto-transport measurements show the enhanced flux pinning force in high fields for both Y123/Y 2 O 3 and Y123/YSZ, being clearer at lower temperatures.

Low-temperature magnetic force microscopy is used for the direct visualization of vortex distribution in high-temperature superconducting films. With the scanning probe microscope (Omicron Cryogenic SFM) magnetic fields up to 7 T (vertical) and 3 T (transversal) can be applied to the sample during in situ imaging at temperatures ranging from 7 K to 300 K in ultra high vacuum. The samples investigated were 300 nm thick YBa 2 Cu 3 O 7− δ films grown epitaxially on SrTiO 3 (0 0 1) substrates by off-axis pulsed laser deposition with a mean roughness less than 10 nm. Prior to imaging, the samples were cooled down in the microscope to 7.7 K in a magnetic field of 3 mT. Flux lines have been successfully imaged by measuring their stray field in the scan height of 40 nm above the sample surface. The number of vortices observed corresponds to the theoretically expected one. Whereas a constant current leads to unacceptable heating of the sample, the use of current pulses allows transport measurements without thermal movement of vortices.

A homogeneous nickel oxide film epitaxially grown on cube textured nickel tapes was prepared as a first buffer layer for subsequent buffer and YBa 2 Cu 3 O x (YBCO) layer depositions. The nickel oxide film was produced under growth conditions of surface oxidation epitaxy (SOE). The preparation of homogeneous oxide films by SOE with a high texture quality and without disturbing columnar oxide growth succeeded on micro-alloyed nickel tapes. Cerium, yttrium and silver are proven beneficial elements for micro-alloying in this respect. In silver doped metallic substrates, the cube oriented grains were produced with an increased grain aspect ratio, which was transferred to the SOE nickel oxide. Increased transport currents in the YBCO coatings were measured in the longitudinal direction of the tapes, which were coated with an additional system of buffer layers. The critical current density reached up to J c = 2.35 MA/cm 2 at 77 K in self field.

A newly developed SrZr1−xTixO3 single perovskite buffer was successfully applied on surface oxidized Ni tapes leading to highly textured YBCO films. An inductively measured Tc above 88 K and inductive Jc values up to 1 MA/cm2 were achieved on Ni–0.1at.%Mo substrates indicating a similar quality as a standard BaZrO3/SrTiO3 double layer.

Ion-beam assisted deposition (IBAD) is a promising technique for preparing highly textured templates on various substrates. A major requirement for the textured nucleation of materials with a rocksalt structure using the IBAD approach is an amorphous seed layer. Metallic Ta0.75Ni0.25 films were used as amorphous layers on Si/Si3N4 as well as on electropolished Hastelloy tapes for the ion-beam assisted pulsed laser deposition of transition metal nitrides. Highly biaxially textured TiN and NbN films have been grown on these layers even at room temperature in a reactive deposition process using an ion beam with an energy of 800 eV under an angle of 45° relative to the substrate normal. The cube texture was preserved to higher thicknesses using homoepitaxial growth. Finally, 10 nm thick Au films were used to study the surface texture quantitatively using x-ray diffraction showing in-plane orientations down to 8°. The results offer the possibility to realize a fully conductive buffer layer architecture for high-temperature superconductors based on the IBAD approach.