La2Zr2O7 Buffer Layers Research Articles

Polymer-assisted chemical solution deposition of high-quality La2Zr2O7 buffer layer applied to low-cost YBCO-coated conductors

Through a simple and low-cost way to gain the precursor solution, high-quality La2Zr2O7 (LZO) buffer layers approximately 300 nm thick only by one single coating were successfully deposited on the textured Ni-5at%W alloy substrates using an independently developed new method of polymer-assisted chemical solution deposition (PA-CSD) with and without Y2O3 seed layer. Highly epitaxial YBa2Cu3O7−x (YBCO) thin film with thickness of 500 nm is managed to be deposited on LZO/Y2O3/NiW. A study was made on the buffers and YBCO films with XRD, AFM, FIB-SEM, ESEM, and through superconducting critical temperature (Tc) analyses, and it was found that the Y2O3 seed layer had a good effect in improving the c-axis texture for the performance of LZO thin films. More importantly, the value of the self-field critical current density (Jc) of YBCO film on LZO/Y2O3/NiW architecture was 1.6 MA/cm2 at 77 K. Our results indicated that the low-cost and effective way to develop high-performance YBCO-coated conductors on the basis of high-quality LZO buffer layer were suitable candidates.

Development and characterization of biaxially-textured lanthanum zirconate film grown on cold-rolled Ni-W substrate by chemical solution deposition

High temperature superconducting tapes based on cuprate compounds are nowadays available on long lengths by several companies. Because high superconducting properties are strongly influenced by the crystallographic orientation of the superconducting film, and because the appropriate crystallographic orientation is obtained through epitaxial film growth, the development of an oriented template is of crucial technological importance. In the rolling assisted biaxially textured substrate (RABiTS) technique, a strong cube texture is obtained by cold rolling fcc metal tape and high temperature annealing, followed by the deposition of one or more buffer layer by either physical vapor deposition (PVD) or chemical solution deposition (CSD). Using the latter approach, it has been recently shown that it is possible to combine substrate recrystallization and buffer layer growth in a single step if the onset of recrystallization occurs at a temperature lower than buffer layer nucleation. In the present contribution, a detailed investigation of biaxially-oriented La2Zr2O7 (LZO) buffer layer grown on cold-rolled Ni-W substrate by combined EBSD, AFM and TEM analyses is reported. It is shown that it is possible to obtain highly {001}〈110〉-textured LZO film directly on cold-rolled Ni-W substrate. Although some small polycrystalline regions appear, this approach leads to a strong suppression of grain boundary grooving typically occurring in RABiT-type substrates. Further, it is shown that, notwithstanding the microstructure of the metal substrate continues to evolve during the conversion heat treatment, the obtained LZO film is well adherent, without cracks or delamination.

Effect of magnetic structural processing on structure and texture of La2Zr2O7 buffer layers

Epitaxial CeO2 seed layer and La2Zr2O7 (LZO) buffer layers were deposited on biaxially-textured Ni–5 at.% W (NiW) tape substrate by liquid-phase polymer assisted nanoparticles deposition (PAND) method. LZO layers deposited by PAND have consistently shown tilting of the [Formula: see text]-axis toward the direction of the sample’s surface normal. A new approach increasing the sharpening of the buffer texture by magnetic structural processing (MSP) of buffer layers was tested. The LZO layers, deposited on the seed and buffer layers after MSP, have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the LZO layers that were deposited on a layer without MSP. Transmission electron microscopy study confirmed the [Formula: see text]-axis tilting of CeO2 and LZO layers and revealed the absence of interfaces between LZO layers which have been grown on the layers after MSP. There are very small (2–4 nm) gated pores in the single-crystal structure of LZO layers that are not typical for structure of LZO layers obtained by liquid-phase methods. Thus the LZO buffer layers can serve as an effective metal-ion diffusion barrier.

Investigation on the texture evolution of epitaxial La2Zr2O7 buffer layer using EBSD techniques

Electron Backscattered Scattering Detection (EBSD) was used to characterize the texture of La2Zr2O7 (LZO) buffer layers prepared by chemical solution deposition on Ni-5at.% W(Ni5W) biaxially textured substrates. We investigated the texture forming process of LZO films with different cation concentrations of the precursor solution. In this paper, the texture evolution mainly depends on the film thickness and on the grain growth. With low cation concentrations in the precursor solution, the discontinuous LZO grains do not completely cover the Ni5W substrates and exhibit large lattice misorientation with respect to Ni5W (defined as cube orientation). A 45° rotation orientation is found to coexist with the cube orientation and is mainly transformed by the cube orientation with increasing thickness. The interface energy minimization may play a dominant role in texture transformation.

Cube texture evolution of Ni5W alloy substrates and La–Zr–O buffer layer of YBCO-coated conductors

The cube texture evolution of Ni-5 at%W alloy deformed up to a very high strain was thoroughly investigated by X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) during the process of deformation, recrystallization and grain growth. A typical copper-type rolling texture, mainly consisting of components of S, copper and brass orientations, is obtained after heavy cold rolling. The fraction of rolling texture is slightly strengthened during recovery and then strongly reduced during recrystallization process. The cube texture is formed by consuming the rolling texture components during the discontinuous recrystallization process. The cube grains have a size advantage with respect to the non-cube grains. A strong cube-textured Ni5W alloy substrate with cube texture area fraction of 98.2 % (<10°) is obtained after annealing at 1050 °C for 1 h. The full width half maximum (FWHM) values for the X-ray (111) φ-scan and the (002) ω-scan of this substrate are 5.84° and 4.76°, respectively. Furthermore, the area fraction of {001} 〈110〉 orientation of the epitaxially grown La2Zr2O7 buffer layer is 97.1 % (<10°), and the FWHM values of (111) φ-scan and (002) ω-scan are 5.22° and 5.00°, respectively.

Thin film deposition based on microacoustic sol atomization (MASA)

In this work, we demonstrate an innovative method for the deposition of functional thin films, based on microacoustic sol atomization (MASA) and subsequent gel condensation. This method offers several advantages over existing sol–gel deposition methods (e.g., ink-jet printing or dip coating), including a narrow droplet-size distribution with droplets in the low micrometer range, a miniaturizable aerosol source and the principle usability in roll-to-roll processes. The technique can be divided into three subsequent steps: In a first step, high-frequency surface acoustic waves atomize precursor solutions (sols) into an ultra-fine aerosol. In a second step, the aerosol condensates on the substrate surface, forming a gel, which in a third step can be pyrolyzed into a crystalline thin film. The new technique is demonstrated for the deposition of La2Zr2O7 buffer layers on biaxially textured Ni–5 %W tapes. Aerosols with median droplet diameters of 4 and 7.5 µm were produced from lanthanum/zirconium precursor solutions based on propionic acid or water, respectively. A continuous aerosol production was maintained for several minutes, allowing a droplet condensation on an area of about 1 cm × 5 cm. X-ray diffraction studies of the crystallized La2Zr2O7 films with a thickness of about 100 nm show a high crystalline quality with a strong (001) orientation. Additionally, our results indicate a significant influence of the fluid chemistry regarding the aerosol formation, as well as the droplet condensation and the thin film formation process, when the impinging droplets contain residual solvent. The deposition of functional thin films by microacoustic sol atomization (MASA) and subsequent condensation is demonstrated here for La2Zr2O7 buffer layers on biaxially textured Ni–5 %W tapes. Aerosols with median droplet diameters of 4 and 7.5 µm were produced via interaction of lanthanum/zirconium precursor solutions based on propionic acid or water, respectively, with high-power surface acoustic waves. A continuous aerosol production was maintained for several minutes, allowing a droplet condensation on an area of about 1 cm × 5 cm. X-ray diffraction studies of the crystallized La2Zr2O7 films with a thickness of about 100 nm show a high crystalline quality with a strong (001)-orientation.

La2Zr2−xCexO7 prepared by chemical solution deposition on Ni–5%W: A promising buffer layer for YBCO-coated conductors

La2Zr2−xCexO7 buffer layers are synthesized by chemical solution deposition on Ni–5%W RABIT substrate. Their structure and microstructure are examined as a function of cerium ratio by x-ray diffraction, atomic force microscopy and electron backscattering diffraction techniques. The composition La2Zr1.9Ce0.1O7 is a very promising candidate as buffer layer for coated conductor tapes. Indeed this Ce-doped layer shows a lower structural mismatch with YBa2Cu3O7−δ, a better texture quality and a smother surface than the classic La2Zr2O7 buffer layer. As a conclusion, this layer presents a high potential to yield a high Jc value in YBa2Cu3O7−δ tapes.

All chemical solution deposition of textured YBa2Cu3O7−x/Y0.2Ce0.8O2/La2Zr2O7 multilayer films on biaxially textured NiW tape

Biaxially textured La2Zr2O7 (LZO) single buffer layer, Y0.2Ce0.8O2 (YCO) single buffer layer, and YCO/LZO bilayer buffer layer are prepared on NiW tapes using chemical solution deposition technique. All the buffer layers are of good in-plane and out-of-plane texture. The introduction of a YCO cap layer on the LZO buffer layer improves the surface quality of the films. YBa2Cu3O7−x (YBCO) films are then prepared on these buffer layers using our recently developed low-fluorine solution route. Purely c-oriented YBCO films with good in-plane and out-of-plane texture are obtained on the YCO/LZO bilayer buffer layers. The YBCO/YCO/LZO/Ni stack prepared using all chemical solution routes shows a high Tc over 90 K, a sharp transition temperature ΔT = 0.8 K, and a Jc of 0.7 MA cm−2(at 77 K, 0T).

Growth of thick La2Zr2O7 buffer layers for coated conductors by polymer-assisted chemical solution deposition

La2Zr2O7 (LZO) epitaxial films have been deposited on LaAlO3 (LAO) (100) single-crystal surface and bi-axially textured NiW (200) alloy substrate by polymer-assisted chemical solution deposition, and afterwards studied with XRD, SEM and AFM approaches. Highly in-plane and out-of-plane oriented, dense, smooth, crack free and with a sufficient thickness (>240nm) LZO buffer layers have been obtained on LAO (100) single-crystal surface; The films deposited on NiW (200) alloy substrate are also found with high degree in-plane and out-of-plane texturing, good density with pin-hole-free, micro-crack-free nature and a thickness of 300nm. Highly epitaxial 500nm thick YBa2Cu3O7−x (YBCO) thin film exhibits the self-field critical current density (Jc) reached 1.3MA/cm2 at 77K .These results demonstrate the LZO epi-films obtained with current techniques have potential to be a buffer layer for REBCO coated conductors.

Texture evolution of chemically deposited La2Zr2O7 buffer layer for coated conductors

A thorough study of the growth and characterization of La2Zr2O7 (LZO) buffer layers prepared by chemical solution deposition on Ni–5at% W biaxially textured substrates is presented. The main focus is to understand the processes of film growth, texture evolution, and lattice misorientation during heat treatment to obtain biaxially textured LZO buffer layers with a high degree of texture. We report a systematic investigation of LZO film growth with varying cation concentrations and processing temperatures. 45° rotated misorientation crystallization is found to coexist with the cube-on-cube orientation and maybe partially formed by the transformation of the cube-on-cube orientation with increasing annealing temperature. The texture component improves with increasing surface crystallinity. These epitaxially grown LZO buffer layers have a dense and smooth structure and a texture component of 98–99%.

Effect of Gadolinium substitutions in La2Zr2O7 films grown on textured Ni-5at.%W substrate by chemical solution deposition

In the YBa2Cu3O7−x coated conductor, the buffer layer is crucial for the texture transfer from the Ni-5%W substrate to the superconducting layer. We developed original La2−xGdxZr2O7 buffer layers (x ≤ 1) by chemical solution deposition to decrease the structure mismatch between the substrate and the buffer layer. They show a strong cube texture up to the surface, a crack free surface and a very low roughness. In conclusion, the La2-xGdxZr2O7 layers with 0.4 < x < 0.9 are promising and should be employed in the future as buffer layer in coated conductor to replace La2Zr2O7 buffer layer.

The precursor manipulation of La2Zr2O7 epi-layers annealed by rapid thermal annealing

This paper reports on the epitaxial growth of a La2Zr2O7 (LZO) buffer layer on the cube-textured Ni-5 at.%W substrate with nitrates as the precursor salts.

Improved textured La2Zr2O7 buffer layers on bi-axially textured Ni–W substrates using CeO2 seed layers for YBa2Cu3O7 − x coated conductors

La2Zr2O7 (LZO) buffer layers were deposited on bi-axially textured Ni–W substrates with CeO2 seed layer by radio-frequency magnetron sputtering for the large-scale application of YBa2Cu3O7−x (YBCO) coated conductors. The microstructure and surface morphology of LZO buffer layers were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy and atomic force microscopy. The influences of substrate temperature and oxygen partial pressure on the microstructure and surface morphology of LZO buffer layers were discussed. It was found that epitaxial LZO films were preferentially c-axis oriented without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c-axis aligned LZO films with no random orientation were obtained at relatively low substrate temperatures of 600–800°C and in flowing 40Pa gas mixtures of Ar–O2 with an effective oxygen partial pressure of 0.1–20Pa. In addition, LZO films grown in low oxygen partial pressure have a smoother surface than films in higher oxygen partial pressure. Then, we fabricated YBCO coated conductors on the high-quality LZO buffer layers by pulsed laser deposition. The critical current density Jc=2.25MA/cm2 and critical current Ic=180A/cm of 0.8-μm-thick YBCO film at 77K, self field were obtained. The magnetic field and angular dependences of critical current per width were discussed. Highly textured LZO films grown on CeO2 seed layer were suitable as a buffer layer for the growth of YBCO coated conductors with high currents.

Tailoring the crystallographic orientation of MOD-derived La2Zr2O7 buffer layers for coated conductors

Well-textured metal-organic-deposited (MOD) Lanthanum Zirconate (La2Zr2O7, LZO) films were spin-coated on biaxially textured Ni–5at.%W substrates for low cost production of YBa2Cu3O7−δ (YBCO) coated conductors. Control of the crystallographic orientation of LZO buffers is of significance to achieve YBCO films with high current carrying capability by means of the selective MOD-seed layer and annealing conditions. X-ray diffraction analysis indicated that the three-layer LZO films on MOD-seed layer, especially MOD–CeO2, showed a significant improvement in out-of-plane and in-plane textures. The surface analysis revealed a typical dense, cracks-free, and homogenous morphology. 500nm-thick YBCO films epitaxially grown on three-layer LZO buffer layers without seed layer, on seed MOD-Y2O3 and MOD-CeO2 by direct-current sputtering, yielded critical current density (Jc) at 77K of 0.6MA/cm2, 1.2MA/cm2 and 1.4MA/cm2, respectively, exhibiting that the superconducting properties were governed by the crystallographic texture of the underlying buffer layer.

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.

Effect of Polymer Inclusion in Preparation of Thick LZO Buffer Layers for YBCO Coated Conductors

In this work, water-based precursor solutions suitable for dip-coating of thick La2Zr2O7 (LZO) buffer layers for coated conductors on Ni-5%W substrates with an inclusion of polymeric polyvinyl pyrrolidone were developed. The effect of varying percentage of the polymer addition on the preparation of the deposited films with maximum crack-free thickness was investigated. This novel water-based chemical solution deposition method involving polymers in two different chelate-chemistry compositions revealed the possibility to grow single, crack-free layers with thicknesses ranging from 140 to 280 nm, with good crystallinity and epitaxial growth. The effect of increasing polymer concentrations on the morphology and the structure of the films was studied. The appropriate buffer layer action of the films in preventing Ni diffusion was studied by X-ray photoelectron spectroscopy.

Growth and Characterization of La2Zr2O7 Buffer Layers Deposited by Chemical Solution Deposition

Abstract The deposition and characterization of La2Zr2O7 thin films deposited by metal-organic decomposition method on both single crystal SrTiO3 and cube textured Ni-5 at.%W substrates are presented. Metal acetylacetonates in propionic acid solution was used. The results showed that LZO films are epitaxially grown with smooth surface with rms roughness around 2 nm. YBa2Cu3O7-δ films, deposited by pulsed laser deposition technique on LZO buffer layers, showed critical temperature of 90 K and critical current density in self magnetic field Jc = 1.6 and 13 MA/cm2 at 77 K and 4.2 K, respectively. A better Jc retention in magnetic field for YBCO films deposited on LZO/STO than YBCO on bare STO is observed indicating a rather strong vortex pinning as confirmed by microwave measurements.

La2Zr2O7 Buffer Layer Prepared on Cube Textured Ni-5at.%W Substrates by a Nitrate Route

This paper states the epitaxial growth of La 2 Zr 2 O 7 (LZO) buffer layers on the cube textured nickel alloy substrate, with the nitrate as the precursor. The solution stability and the heat treatment processing were discussed respectively. The solution of hydrated nitrates dissolved in ethanol being a sol at a higher temperature, the precursor was pre-dried and methanol was substituted with a higher dielectric constant. Because of the multi-step decomposition of the nitrates, a multi-step heat treatment route was followed, the complete decomposition of the intermediate phases being essential. The orientation analysis shows a cube textured film with the FWHM values of the (222) phi-scan and of the (400) ω-scan being 8.50° and 8.10° respectively. The SEM image shows a dense and homogeneous film without cracks and holes. The analysis above indicates that the present route is feasible for the preparation of LZO buffer layers

Fabrication of highly textured Ni–7at.%W substrates and further application for coated La2Zr2O7 buffer layer

In this work, highly cube textured Ni–7at.%W (Ni7W) substrate was fabricated from the ingots synthesized by Spark Plasma Sintering (SPS) technique. Both the La2Zr2O7 (LZO) buffer layer and the YBCO superconducting layer were coated using chemical solution deposition (CSD) and pulsed laser deposition (PLD) layer by layer. The full-width-at-half-maximum (FWHM) values of the (111) phi-scan and the (200) ω-scan in rolling direction of the Ni7W substrate were 6.30° and 5.08°, respectively. The EBSD analyses indicated that the percentage of the cube texture component on the surface of the as-obtained Ni7W substrate was 99.4% within a tolerance angle of less than 10°. Highly epitaxial growth of homogenous crack-free LZO film was obtained cube-on-cube relative to the Ni7W substrate, with FWHM values of (222) phi-scan and (400) ω-scan of 7.57° and 5.73°, respectively. The critical temperature of the YBCO layer prepared on LZO/Ni7W substrate is about 90.5K, while the critical current density is 1.25MAcm−2 (77K, sf).

Preparation of ${\rm CeO}_{2}/{\rm La}_{2}{\rm Zr}_{2}{\rm O}_{7}$ Buffer Layers on Textured Ni5W Substrates by Chemical Solution Deposition Method

CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> caped La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (LZO) buffer layers on cube-textured Ni5W substrates were fabricated by the method of chemical solution deposition(CSD). The orientation of both LZO film and CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /LZO buffer layer was investigated using conventional XRD and X-ray four circle diffractometers, respectively. The results reveal that both the LZO film on Ni5W substrates and CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film on LZO buffer layer are grown epitaxially. The value of Full Width at Half Maximum (FWHM) of (111) Phi scan of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /LZO buffer layer is around 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> , and the FWHM of (200) omega-scan of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> buffer layer is 6.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> , indicating a good in-plan orientation of the as obtained buffer layers. It was observed by the high resolution SEM that the surface of LZO buffer layer is crack-free and very dense. The surface result observed by AFM indicates a very smooth CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surface with 5.9 nm of the root mean square roughness measured in an areas of 30 times 30 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . AES depth profile results of CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /LZO buffer layers shows that the deposited LZO film could effectively prevent the diffusion of Ni into the buffer layer.