Textured Ni-W Substrates Research Articles

Preparation of biaxially textured Ce1-x(Y0.2Zr0.8)xOδ buffer layers on RABiTS NiW tapes by chemical solution deposition

Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00 l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor.

Effect of post-annealing in low oxidizing atmosphere on the properties of CeO2 buffer layer for coated conductors

CeO2-x thin films have been fabricated by chemical solution deposition (CSD) technique on bi-axial textured Ni5W substrates. The effect of post-annealing in moderate oxidizing atmosphere on the structure and texture of the film has been studied by varying temperature and CO2 concentration during the post-annealing process. The results show that the structure and texture stability of the CeO2-x film is heavily dependent on the post-annealing temperature. A high post-annealing temperature could lead to the change of cerium valence and even oxidation of Ni5W substrate. In addition, an excess amount of CO2 could cause the degeneration of texture degree and surface flatness of CeO2-x film because of the increase of oxygen vacancy defects and the production of carbonates. Except effective removal of residual carbon in films, therefore, the production of both the oxygen vacancy concentration and carbonates should be greatly controlled to improve the texture degree and surface flatness of CeO2-x films by adjusting the concentration of oxidizing gas and the heat-treatment temperature during the post-annealing process or the YBCO deposition process. Moreover, the CeO2-x film post-annealed at 700 °C in the mixture atmosphere with 1% CO2 show sharper texture and smoother surface because of the existence of small amount of oxygen vacancy and carbonates compared with the as-prepared sample.

Magnetic granularity in pulsed laser deposited YBCO films on technical templates at 5 K

The manifestation of granularity in the superconducting properties of pulsed laser deposited YBCO films on commercially available metallic templates was investigated by scanning Hall probe microscopy at 5 K and was related to local orientation mapping of the YBCO layer. The YBCO films on stainless steel templates with a textured buffer layer of yttrium stabilized ZrO2 grown by alternating beam assisted deposition have a mean grain size of less than with a sharp texture. This results in a homogeneous trapped field profile and spatial distribution of the current density. On the other hand, YBCO films on biaxially textured NiW substrates show magnetic granularity that persists down to a temperature of 5 K and up to an applied magnetic field of 4 T. The origin of the granular field profile is directly correlated to the microstructural properties of the YBCO layer adopted from the granular NiW substrate which leads to a spatially inhomogeneous current density. Grain-to-grain in-plane tilts lead to grain boundaries that obstruct the current while out-of-plane tilts mainly affect the grain properties, resulting in areas with low . Hence, not all grain boundaries cause detrimental effects on since the orientation of individual NiW grains also contributes to observed inhomogeneity and granularity.

Tailoring Microstructure and Superconducting Properties in Thick BaHfO3 and Ba2 Y(Nb/Ta)O6 Doped YBCO Films on Technical Templates

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.

Thickness-Dependent Properties of YBCO Films Grown on GZO/CLO-Buffered NiW Substrates

To study the role of novel Gd\(_2\)Zr\(_2\)O\(_7\)/Ce\(_{0.9}\)La\(_{0.1}\)O\(_2\) buffer layer structure on a biaxially textured NiW substrate, a set of YBa\(_2\)Cu\(_3\)O\(_{7-\delta }\) (YBCO) films with different thicknesses were prepared by pulsed laser deposition (PLD). Interface imperfections as well as thickness-dependent structural properties were observed in the YBCO thin films. The structure is also reflected into the improved superconducting properties with the highest critical current densities in films with intermediate thicknesses. Therefore, it can be concluded that the existing buffer layers need more optimization before they can be successfully used for films with various thicknesses. This issue is linked to the extremely susceptible growth method of PLD when compared to the commonly used chemical deposition methods. Nevertheless, PLD-grown films can give a hint on what to concentrate to be able to further improve the buffer layer structures for future coated conductor technologies.

X-ray photoelectron spectroscopic studies of CeO2 thin films deposited on Ni-W (100), c-Al2O3 (0001) and Si (100) substrates

The oxidation states of CeO2 films, deposited on biaxially textured Ni-W(100), c-Al2O3(0001) and Si(100) substrates, were investigated by using X-ray photoelectron spectroscopy (XPS). The CeO2 films were deposited by RF magnetron sputtering under same deposition conditions. X-ray diffraction (XRD) studies of the films revealed that preferred (200) orientation of CeO2 was observed in case of Ni-W substrate while (111) orientation on Al2O3 and Si substrates. The O1s and Ce3d spectra reveal that the films mostly consist of Ce4+ oxidation states with ∼72.6%, 74.7% and 74.9% on Ni-W, Al2O3 and Si substrates, respectively. The less Ce4+ content in case of Ni-W substrate has been attributed to the migration of oxygen atoms from film to the metallic substrate. The decrease of O2p states in the valence band spectra also in support with the presence of more oxygen vacancies in CeO2/Ni-W compared to that in other substrates. Further, the position of valance band maxima is almost identical (∼2.6 eV) for all the deposited films indicating that all films are n-type in nature.

Ultrafast pump-probe spectroscopy studies of CeO2 thin film deposited on Ni-W substrate by RF magnetron sputtering

This study presents the first investigation of rapid dynamical processes that occur in pure CeO2 thin film, using ultra fast pump-probe spectroscopy at room temperature. For this purpose we have used a single (200) oriented CeO2 film deposited on biaxially textured Ni-W substrate by RF magnetron sputtering technique. The ultrafast transient spectra show initial sharp rise transition followed by an exponential photon decay. This rise time is about 10 ps irrespective of the probe wavelengths range 500–800 nm. The initial decay constant (τ) at 500 nm probe wavelength is found to be 171 ps, while at 800 nm probe wavelength it is 107.5 ps. The ultrafast absorption spectra show two absorption peaks at 745 and 800 nm, and are attributed to the electronic transitions from 2F7/2–2F5/2 and 1S0–1F3 respectively. The relatively high intensity absorption peak at 745 nm indicates dominant f–f electronic transition. Further, the absorption peak at 745 nm splits into two distinct peaks with respect to delay time, and is attributed to the charge transfer in between Ce4+ and Ce3+ ions. These results indicate that CeO2 itself is a potential candidate and can be used for optical applications.

Epitaxial growth of CSD modified lanthanum zirconium oxide buffer layer for coated conductors

Texture and morphology evolution of modified Lanthanum Zirconium oxide (LaZr1.1Oy) films grown on biaxially textured Ni5%W tapes by chemical solution deposition (CSD) method at different heat-treatment conditions has been investigated. Results show that both the growth orientation and surface morphology of films are dependent on the heating rate and annealing temperature during heat-treatment process. Compared with the annealing temperature, heating rate shows a greater influence on the orientation growth of CSD-LaZr1.1Oy film. Slow heating rate is beneficial to a single (00l) orientation growth of LaZr1.1Oy grains on textured Ni-5at.%W (Ni5W) substrate. However, the surface morphology analysis reveals a minor effect of heating rate on the grain size and surface roughness of LaZr1.1Oy film. We consider that a slow heating rate would lead to the homogeneity nucleation of LaZr1.1Oy grains and eventually forming the great textured film due to the narrow temperature interval of the complete decomposition for LaZr1.1Oy precursor gel. In any case, high-quality LaZr1.1Oy film has been achieved at annealing temperature of 900 °C with heating rate of 2 °C/min. Moreover, we have grown epitaxial CeO2 film on the textured Ni5W substrate covered by LaZr1.1Oy film using CSD approach. CeO2 precursor solution was spin-coated on short sample of Ni5W/LZO and then heat-treated at 1000 °C for 30 min in Ar-4%H2. Detailed XRD and AFM studies indicate that CeO2 film has sharp bi-axial texture and smooth surface. These results demonstrate that a low-cost CSD LaZr1.1Oy film can act as a planarization template for the further production high Jc YBCO-superconducting film.

Improved morphological and barrier properties of lanthanum zirconium oxide buffer layers obtained by chemical solution deposition for coated conductors

Lanthanum Zirconium oxide buffer layers with a narrow compositional window of LaZrxOy (x = 0.7–1.3) have been grown on textured NiW substrates by chemical solution deposition (CSD). X-ray diffraction analysis indicates that a single epitaxial LZO phase with well bi-axial texture can be obtained in a narrow compositional range of x = 0.7–1.1 in LaZrxOy, while higher x value yields incompletely (00l) textured films. Morphological and barrier properties have been investigated by atomic force microscopy (AFM) for as-grown samples and X-ray diffraction (XRD) for the re-annealed samples in an oxidizing atmosphere. AFM images indicate a dramatic improvement of surface plateness for LaZrxOy (x > 1) film with respect to LaZrxOy (x = 1) with standard composition. Barrier properties of LZO show an obvious increasing trend with the increase of x value in LaZrxOy, which may be related to the change of the intrinsic oxygen diffusion coefficient for buffer layers with different compositions. The improvement of surface planeness and barrier property in buffer layer is the key towards obtaining epitaxial YBCO films with a higher critical current density. Therefore, the present result demonstrates a promising route for producing low-cost and high-performance coated conductors.

Single Oriented CeO2 Buffer Layer Deposition On Biaxially Textured Ni-W Substrate By RF Magnetron Sputtering

Considerable attention has been gained on the deposition of CeO2 thin films with (200) single orientation as hetero-epitaxial buffer layer on (200) oriented biaxially textured flexible Ni substrates, in the fabrication of superconductor and semiconducting epitaxial thin films for device applications. In this work we have deposited (200) oriented CeO2 thin films on biaxially textured Ni-W substrate in a single-step process by RF magnetron sputtering, using CeO2 target. X-ray diffraction analysis shows that for the CeO2 thin film deposited at RF sputtering power below 200 W and for the substrate temperature of 700 o C, the film assumes single (200) orientation. For the substrate temperature below 700 o C and RF sputtering powers above 200 W the film shows polycrystalline nature with (111) and (200) orientations. The Raman spectrum of single oriented (200) CeO2 thin film shows only one sharp peak at about 464 cm -1 corresponds to the presence of F2g mode of CeO2. The ellipsometry studies reveal the value refractive index and optical band gap of single oriented film as 2.52 and 3.41 eV, respectively. Copyright © 2015 VBRI Press.

Growth And Field Emission Properties Of Vertically-aligned ZnO Nanowire Array On Biaxially Textured Ni-W Substrate By Thermal Evaporation

Vertically well aligned and highly dense ZnO nanowires (NWs) have been grown on biaxially textured Ni substrates by a simple thermal evaporation technique over a large area without using any catalyst. The grown ZnO NWs have crystallized in wurtzite hexagonal structure and have grown along [0001] direction. It is also observed that the degree of vertical alignment of NWs increases with increasing growth temperature. An intense photoluminescence peak at 383 nm with a negligible deep band emission revealed the good crystalline quality of ZnO NWs. Field emission properties of the grown NWs have been examined and a field enhancement factor of 1573 has been obtained, indicating the suitability of grown nanowires for field emission applications. Copyright © 2015 VBRI Press.

Epitaxial growth of Ba2YNbO6 films on biaxially-textured NiW substrates as a multifunctional single buffer layer for high Jc epitaxial YBCO film

Abstract

Growth of thick MOD-derived CeO2−x buffer layer with less residual carbon for coated conductors

120 nm thick CeO2−x buffer layer with less residual carbon has been prepared on biaxially textured NiW substrate using a newly developed heat-treatment route by a metal organic deposition approach. The thickness enhancement of CeO2−x buffer layer was achieved by multiple coatings. The residual carbon removal in CeO2−x buffer layer was realized by introducing CO2 into annealing atmosphere at the post-annealed step. Various characteristic methods, including X-ray diffraction, X-ray photoelectron spectra, emission scanning electron microscopy and atomic force microscopy analyses techniques have been applied to investigate the performance of CeO2−x film. The results show that thick high-quality textured CeO2−x film with smooth and crack-free surface has been produced at annealing temperature below 1000 °C. Furthermore, the atomic concentration of C in such thick CeO2−x buffer layer prepared using the post-annealed step by introducing CO2 into annealing atmosphere is obviously less than that in CeO2−x film fabricated in reducing atmosphere of Ar–4 % H2. In addition, the introduction of CO2 into post-annealing step is helpful to the decrease of oxygen vacancy defects in CeO2−x film, which can suppress the generation of cracks in film. It suggests that CeO2−x film fabricated by the newly developed heat-treatment route is proved to be a strong candidate as a buffer layer used for the further growth of the oxide film in coated conductors.

Growth And Characterization Of Large Grained Poly-Si Films Grown On Biaxially Textured Ni-W Substrate By Hot-wire CVD

Polycrystalline Si (Poly-Si) film with highly crystalline nature, and having most of the grains in the range of 50-100 µm has been grown over biaxially textured Ni-W substrate by Hot-wire chemical vapor deposition technique, using a single buffer layer of CeO2 thin film. This result has been achieved for the SiH4 source gas diluted to 95% with added H2 gas, and for the substrate temperature of 840±10oC and a deposition pressure of 40 mTorr. XRD analysis shows that the Poly-Si films have grown with (111) and (200) orientations. Raman studies reveal that a crystalline volume fraction of 95.3% has been achieved. The imaginary part of pseudo dielectric function, <ε2>, as extracted from ellipsometric data, shows two prominent shoulders at energy positions 3.4 eV and 4.2 eV corresponding to the optical absorption of crystalline Si, indicating a high crystallinity of the Poly-Si film. SEM micrograph shows that the grown Poly-Si film is following the morphology and grain size as that of biaxially textured Ni-W substrate. SIMS analysis of the total multilayer structure shows a formation of very sharp interfaces, with no diffusion between Si and Ni, indicating that a single buffer layer of CeO2 is sufficient to avoid the formation of nickel silicide while growing Si over Ni substrate. Thus, these results are very encouraging for the fabrication of Poly-Si film based solar cells with increased efficiency by minimizing the undesired recombination of charge carriers at grain boundaries.

Application of spray deposition techniques for fabrication of Sm-doped CeO2 thin films on biaxially textured Ni-W substrate

Chemical and thermo-resistant buffer layers are commonly used to separate metal substrates and high-temperature superconductors (HTS). This ensures that no reaction occurs between the superconductor's precursor materials and the substrate metal during high-temperature HTS tape processing. Various materials and coating procedures are available, with each combination of buffer layers requiring specific characteristics. This paper reports a feasibility study into the development and use of simple, aerosol-based production methods of samarium-doped cerium thin films for subsequent use as a buffer layer between a Ni substrate and yttrium barium copper oxide (YBCO) superconductor. The suggested methods are very cost effective and hence attractive for commercial use. It was shown that different types of aerosol nebulisers can produce textured, pinhole-free films of high integrity and uniformity. Thickness of the films could be precisely controlled by the deposition time enabling achieving any required value starting from 40nm. It was found that that the optimum film thickness is between 120 and 180nm, and higher film thickness led to the surface cracking. Microstructural and crystallographic characteristics, and chemical composition of fabricated films are also reported and discussed.

Synthesis of CeO2 microcrystals fabricated on biaxially textured Ni-W substrate by using an e-beam evaporation technique

Cerium-oxide (CeO2) microcrystals have been synthesized on a biaxially textured Ni-5%W (200) substrate by using the Electron beam (e-beam) evaporation technique with CeO2 powder as the source material. The substrate temperature and electron beam gun power at which the microcrystals were formed were 400°C and 400 W, respectively. The X-ray diffraction (XRD) analysis confirmed the crystallinity and a (111) orientation of the CeO2 crystals. Scanning electron microscope (SEM) image showed that the CeO2 crystals had large lateral dimensions in the range from 0.5 to 2.0 μm. The Raman spectrum shows only one peak at 464 cm−1 corresponding to the of F2g mode of the CeO2 crystals. No reports are available on the preparation of CeO2 crystals with such a large size on textured Ni-W substrate by using e-beam evaporation technique.

Oriented Sm-doped CeO2 thin films on biaxially textured Ni-W substrate produced by ultrasonic spray deposition

A new method of producing Sm-doped CeO2 thin films on metal substrates using an ultrasonic nebuliser has been developed and experimentally verified. Sm-doped CeO2 films with a thickness down to 50nm and the required properties were consistently and cost effectively produced on Ni–W textured substrates. High film uniformity and c-axis crystal orientation were confirmed by electron microscopy and X-ray diffraction. Characteristics of films and elements valence states are discussed. Our results suggest that the techniques used are promising for further development of buffer layer formation for textured high-temperature superconducting tape applications.

Study of Ta-doped CeO2 Buffer Layer for Coated Conductors

Abstract Ta-doped CeO 2 buffer layers were grown on the home-made textured Ni-5W substrates for YBCO coated conductors by a simple metal-organic deposition technique. The characterization of the samples was discussed. XPS results indicate that Ta 5+ is reduced into Ta 4+ prior to Ce 4+ , which is helpful to suppress the formation of holes and cracks in CeO 2 films from reducing Ce 4+ into Ce 3+ . Additionally, no new phase is found by doping Ta into CeO 2 , which indicates that Ta 4+ replaces the Ce 4+ position in CeO 2 lattice to form Ce 0.75 Ta 0.25 O 2 . The Ce 0.75 Ta 0.25 O 2 has a good out-of-plane and in-plane texture FWHM values for ω scan and ϕ scan are 4.38° and 6.67°, respectively. AES measurements show that no Ni element is detected on the surface of Ce 0.75 Ta 0.25 O 2 film, and a one-layer film has a thickness of about 70 nm. It is promising that the presently developed Ce 0.75 Ta 0.25 O 2 film can be used as a single multi-functional buffer layer for coated conductor.

X-ray photoelectron spectra and composition of YBa2Cu3O7 − δ films prepared by laser ablation

The Y3d, Ba3d 5/2, Cu2p 3/2, and O1s X-ray photoelectron spectra of thick (600 nm) superconducting YBa2Cu3O7 − δ films deposited on textured Ni-W substrates with Y2O3 + ZrO2 and CeO2 buffer layers have been studied. It has been established that, after the mechanical removal of surface layers with a diamond scraper (and as the analyzed region of the film approaches the interface), a decrease in the oxygen content leads to a decrease of the orthophase fraction and an increase of the tetraphase and Cu+ ion fractions. This is caused by the presence of elastic stresses in the superconducting film due to the lattice misfit between the phases making up a composite sample. These stresses prevent oxygen diffusion involved in oxidizing annealing. The spectra of the superconducting film have not revealed signals generated by elements of the substrate and buffer layers.

Epitaxial growth and characterization of La2Zr2O7 multilayers on biaxially textured NiW substrate by chemical solution deposition under highly reducing conditions

The paper presents the growth and characterization of highly textured La2Zr2O7 (LZO) multilayer coatings on Ni–5at.%W (NiW) biaxially textured substrates by chemical solution deposition (CSD) under highly reducing conditions (Ar+12%H2) in order to protect the metallic substrate from oxidation. The coating solution consists in a stoichiometric mixture of lanthanum and zirconium acetylacetonates dissolved in an excess of propionic acid. The precursor chemistry was studied by means of infrared spectroscopy, thermogravimetric–differential thermal analyses, Raman spectroscopy and X-ray diffraction carried out on the precursor powder. The as-grown multilayer LZO coating exhibits a sharp in-plane and out-of-plane texture, with the full-width-at-half-maximum of the ω-scans and φ-scans of about 7.2° and 8.0°, respectively, close to that of the NiW substrate. The volume fraction of the c-axis oriented grains from the top layer of the coating increases with the number of layers. The LZO coating exhibits a smooth and crack-free surface, appropriate for the further epitaxial growth of a seed layer for the YBa2Cu3O7−x (YBCO) deposition. Transmission Electron Microscopy was used to investigate the microstructure of the CSD LZO thin films deposited on flexible NiW substrates. A high density of nanovoids, with a size ranging between 10 and 30nm, was observed in the LZO layers. YBCO films epitaxially grown by pulsed laser deposition on the CSD LZO buffer layer exhibit critical current densities, Jc, close to 1.6MA/cm2 at 77K and self-field and zero resistance critical temperature (Tc(R=0)) of 90.3K.