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Using the magnetic sputtering technique, the SnO2/Ag/SnO2 tri-layer transparent films were fabricated on float glasses successfully. Compared with the commercial FTO (F-doped SnO2) film, the SnO2/Ag/SnO2 tri-layer films have higher visible-light transmittance and better conductivity. The total thickness of the SnO2/Ag/SnO2 films is one third of the commercial FTO film leading to the high visible-light transmittance. The high carrier concentration of the SnO2/Ag/SnO2 films contributes to the tri-layer films’ low resistivity. In addition, to further improve the performance of the SnO2/Ag/SnO2 tri-layer films, samples were annealed under different temperatures. The results illustrate that the lowest sheet resistance (5.92 Ω/sq) and the highest visible-light transmittance (87.0%) were obtained after annealing at 200 °C. Furthermore, the thermal stability of the films could be enhanced by a multi-step annealing process due to the recrystallization effect.

Thickness effect severely limits the performance of REBa2Cu3O7-δ coated conductors. In this work, a Y0.5Gd0.5B2C3O7-δ/LaGdZr2O7/Y0.5Gd0.5Ba2Cu3O7-δ (YGdBCO/LGZO/YGdBCO) tri-layer film was fabricated by pulse laser deposition, which successfully inhibited the thickness effect and improved the superconductivity of YGdBCO film. By investigating the microstructure of the inserted LGZO layer, it was found that LGZO interlayer can not only reduce the surface roughness of the bottom YGdBCO layer by inhibiting the continuous growth of YGdBCO crystal grains but also realize the transmission of current between superconducting layers. With the deposition of LGZO interlayer, the critical current of the YGdBCO film increased significantly by nearly 50% from 180 A of a double-layer YGdBCO film with the same thickness to 270 A. Transmission Electron Microscope (TEM) observation and Energy Dispersive Spectroscopy (EDS) analysis indicate that the incomplete oxidized particles in the LGZO layer serve as the current channels between YGdBCO layers in the samples prepared at a laser energy of more than 210 mJ.

SrTiO3 films were deposited using pulsed laser deposition (PLD) at substrate temperatures ranging from 300 °C to 700 °C on a CeO2 layer and nano-Y0.5Gd0.5Ba2Cu3O7-δ buffered CeO2 layer, respectively. The effect of the substrate temperature and substrate film on the crystallinity, preferred orientation, and surface topography were investigated. On the CeO2 layer, there were two preferred SrTiO3 orientations, (00l) and (110). By introducing a nano-Y0.5Gd0.5Ba2Cu3O7-δ layer, pure c-axis oriented SrTiO3 films were obtained at each substrate temperature. Based on the lattice mismatch, three kinds of growth modes of SrTiO3 grains were proposed that were proved by scanning electron microscopy (SEM).

To evaluate the inhibition of the REBa2Cu3O7-δ (REBCO, where RE is rare earth) film thickness effect, a series of Y0.5Gd0.5Ba2Cu3O7-δ(YGBCO)/interlayer/YGBCO tri-layer films with Gd-Cerium oxide (CeO2) film were prepared under different experimental conditions in this study. The results illustrate that the electric current from the top YGBCO layer could transmit to the bottom YGBCO layer by adding Gd into the CeO2 interlayer with the approximate thicknesses limits of 10 nm. For further increase the electric current carrying capacity, a series of YGBCO/Gd-CeO2/YGBCO tri-layers were fabricated under different oxygen partial pressures and laser energies. The better crystallinity, and texture, and the smoother surface levels completely eliminated the thickness effect. However, the samples’ superconductivity declined sharply at low laser energies. Because the Gd particles deposited on the substrate were fully oxidized, this led to particle disappearance in the interlayer film. Additionally, YGBCO samples with a Gd-CeO2 interlayer were more likely to be damaged than a pure YGBCO sample in the measurement process, which could be solved by increasing the Gd content in the CeO2+Gd target. Hence, by depositing a Gd-CeO2 interlayer, YGBCO tri-layer films with high superconductivity and low damageability were obtained.

High critical current (Ic) has long been proved important to REBa2Cu3O7−δ (REBCO or RE123) superconductor for the practical applications. To achieve high Ic values, the primary way is to increase the thickness of superconducting layer and to enhance high critical current density (Jc). However, Jc drops precipitously with increasing the thickness of the films. This phenomenon is called the thickness effect, which can be effectively inhibited by fabricating superconductor/interlayer/superconductor tri-layer structure. In this study, a series of YGBCO/CeO2/YGBCO and YGBCO/In doped CeO2 (CeO2 + In)/YGBCO tri-layer films with different interlayer thickness were fabricated. The microstructure, surface morphology and superconducting property of these samples were measured. It was found that all the tri-layer films had pure c-axis orientation. When using CeO2 film as an interlayer, the two YGBCO layers in the tri-layer films were almost completely isolated, resulting in the low Ic values, which were equivalent to the Ic of a single YGBCO layer. While using CeO2 + In film as an interlayer, the Ic values of all the YGBCO/CeO2 + In/YGBCO trilayers were almost double the Ic of a single YGBCO layer, and the Ic values of the trilayers firstly slow increased and then decreased with increasing the thickness of CeO2 + In interlayer. Under the optimal experimental parameters, the Ic value was much higher than that of the a double YGBCO layer without interlayer. The thickness effect of superconducting layer can be effectively inhibited by inserting CeO2 + In interlayer with wide thickness range.

The surface morphology and internal residual stress have influence on the critical current density (Jc) of REBa2Cu3O7-σ (REBCO) coated conductor. In order to modulate them, a series of Y0.5Gd0.5Ba2Cu3O7-σ (YGBCO) films were prepared by pulsed laser deposition (PLD) through introducing a seed layer in this paper. The thicknesses of seed layer changes from about 2 nm to 30 nm. For comparison, a standard sample without seed layer was fabricated at the same deposition condition. The surface morphology was illustrated by Scanning electron microscopy (SEM). The surface roughness was scanned by Atomic force microscopy (AFM). The microstructure and internal strain were measured by X-ray Diffraction (XRD). DC four-probe method was used to measure the critical current of the samples at 77 K and self-field. As a result, all samples have high Jc of about 4 MA/cm2, while the self-field Jc of the YGBCO films can be promoted by the seed layer. The results of our research work are as follows. First of all, seed layer makes the deposition of the YGBCO layer much easier to control. By this way, we can decrease the surface roughness of the samples. Furthermore, the internal residual stress of the YGBCO films with seed layer decrease. Finally, the best thickness of the seed layer was found by summarizing and analyzing the conditions of seed layer.

As an emerging technique for surface smoothing, solution deposition planarization (SDP) has recently drawn more attention on the fabrication of the second generation high temperature superconducting (2G-HTS) tapes. In our work, a number of amorphous oxide layers were deposited on electro-polished or mirror-rolled metallic substrates by chemical solution route. Topography evolution of surface defects on these two types of metallic substrates was thoroughly investigated by atomic force microscopy (AFM). It was showed that root mean square roughness values (at 50 × 50 μm 2 scanning scale) on both rough substrates reduced to ∼5 nm after coating with SDP-layer. The smoothing effect was mainly attributed to decrease of the depth at grain boundary grooving on the electro-polished metallic substrate. On the mirror-rolled metallic substrates, the amplitude and frequency of the height fluctuation perpendicular to the rolling direction were gradually reduced as depositing more numbers of SDP-layer. A high J c value of 4.17 MA cm −2 (at 77 K, s.f. ) was achieved on a full stack of YBCO/CeO 2 /IBAD-MgO/SDP-layer/C276 sample. This study enhanced understanding of the topography evolution on the surface defects covered by the SDP-layer, and demonstrated a low-cost route for fabricating IBAD-MgO based YBCO templates with a simplified architecture.

CeO2 film plays an essential role in nucleation and growth of YBa2Cu3O7−x (YBCO) films. In this work, the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated, in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction (XRD), atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED). Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum (FWHM) values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square (RMS) roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope (TEM) cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface, while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density (J c) as high as 4.6 × 106 A·cm−2 (77 K, self-field) is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2O3/Al2O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.

So far, huge progress has been achieved in coated superconductor wires with high performance, where cerium oxides (CeO2) usually figure as superior buffer layer. However, the influence of CeO2 layer’s surface morphology on the performance of YBCO layer is still illusive. In this work, we fabricated CeO2 layers with similar texture and diverse surface characteristics by altering process parameters on IBAD-MgO substrate and then deposited YBCO layers on these CeO2 layers by a reel-to-reel pulsed laser deposition (PLD) system. The abnormal relationship between the quality of YBCO layer and the surface morphology of CeO2 layer was investigated. Instead of texture quality, the critical current density of YBCO-coated layer is highly susceptible to the surface morphology of CeO2 layer, once their surface roughness root mean square (RMS) outstrips the threshold of atomic flat. And our study indicates RMS and flat area fraction are all key issues for PLD epitaxial multilayers but play in different priority. The possible defect formation process of YBCO/CeO2 was also discussed on the basis of the SEM images.

High-quality long REBCO-coated conductors have been successfully fabricated on flexible metal substrates by pulsed laser deposition (PLD). Although thinner REBCO films had a very high critical current density J c of 5.0 × 10 6 A/cm 2 (at 77 K, in zero magnetic field), J c of thick films decreased to less than 3.0 × 10 6 A/cm 2 as the thickness increased over 1 μm. In order to improve superconducting properties of REBCO thick films, microstructure and surface morphology of different thick REBCO films were systematically analyzed to understand the relationship between J c and epitaxial growth process. X-ray diffraction (XRD) analysis showed that thick REBCO films still had pure c-axis orientation by Gd substitution and Y 2 O 3 doping. Scanning electron microscope (SEM) images showed thick REBCO films with high J c had sub-micrometer size grains and narrow grain-boundaries. Our experimental results showed REBCO thick films with I c of 780 A/cm could be obtained. Hundred meters long coated conductor tapes with 500 A/cm have been routinely fabricated. And now, the process optimization for kilometer long coated conductor tapes is underway.

MgO thin films were grown on Y2O3/Al2O3 buffered C276 tapes by ion beam assisted deposition (IBAD) method and the effects of assisting ion beam current on their microstructure and surface morphology were investigated. In order to evaluate the quality of IBAD-MgO thin films, CeO2 cap layer was deposited directly on the IBAD-MgO template and then YBCO superconducting layer was grown by pulsed laser deposition (PLD) method. Film characterization was performed by in-situ reflection high energy electron diffraction, X-ray diffraction, and atomic force microscopy. The critical current Ic of the YBCO film was measured by the conventional four-probe method. It was found that the orientation, texture degree and surface morphology of the IBAD-MgO thin films were very sensitive to assisting ion beam current. By optimizing the assisting ion beam current, IBAD-MgO thin films had pure (002) orientation, excellent biaxial texture and very smooth surface with a root mean square surface roughness of less than 1 nm. The PLD-CeO2 layer had the best out-of-plane texture of Δω = 1.6° and in-plane texture of Δφ = 4.8° at 140 mA of assisting ion beam current. Under optimized experimental condition, high quality YBCO coated conductor with the critical current density Jc of 4.5 × 106 A/cm2 was fabricated at 77 K and self field.

In China, the First National Key Project on CC Program started in 2009, which was focused on developing hundred meter long class CC tapes based on PLD/RABiTS processes. In this project, SJTU mainly worked on all of functional layer deposition process development. Northwest Institute for Non-ferrous Metal Research worked on RABiTS tape fabrication. At the end of the project in 2011, SJTU successfully fabricated hundred meter long CC tapes with over 300 A/cm (at 77 K, self field) on RABiTS tapes. To develop high performance CC tapes by PLD/IBAD-MgO processes, a pilot CC fabrication line was set up at Shanghai Superconductor Technology Corporation, Ltd. in 2013. High quality long REBCO coated conductors have been successfully fabricated on flexible polycrystalline metal tapes by PLD plus magnetron sputter and IBAD processes. Under optimized conditions, the IBAD-MgO layers showed pure (0 0 1) orientation and excellent in-plane texture. The in-plane phi-scan rocking curve is 4–6 degrees. AFM observation showed MgO layer had very smooth surface. The RMS is less 1 nm. On the textured MgO layer, sputter deposited single cerium oxide cap-layer showed pure (0 0 1) orientation and excellent in-plane texture of 4–6 degree. Reel-to-reel PLD process with high deposition rate was already scaled up to 100 m/h tape speed. Hundred meters long coated conductor tapes with over 500 A/cm performance have been routinely fabricated. And now, the process optimization for kilometer long coated conductor tapes is underway.

Yttria-stabilized zirconia (YSZ) films are deposited on CeO2/NiW tapes by RF sputtering for (Gd) BCO-coated conductors. Surface morphology and texture developments are investigated as the O2 : Ar ratio and sputtering power increase. Both the grain size and the roughness of YSZ films increase as sputtering power increases. A simple model proposed by Bartelt et al. is used to explain the results. The strain relaxation mechanism plays a major role in the sudden increase in roughness for YSZ film deposited at a sputtering power of 50 W. It is observed that low O2 : Ar ratio favors the growth of (200) orientation for YSZ film, while high O2 : Ar ratio favors the growth of (111) orientation. The preferential orientation (200) of the YSZ film with low O2 : Ar ratio arises from template effect of CeO2 buffer layer. The (111) orientation of YSZ film with high O2 : Ar ratio is due to thermodynamic mechanism aiming for the lowest surface energy. The grain size and roughness of our optimal YSZ film are 10–15 nm and 0.7 nm, respectively. The out-of-plane texture of our optimal YSZ film is 4.05°. The in-plane texture is 6.35°. The plan view and cross-section SEM images of YSZ films on CeO2/NiW tapes show a flat, dense and no micro-cracks morphology. Based on these results, (Gd) BCO films are deposited by RF sputtering, achieving self-field Jc of 4.0 MA/cm2 at 77 K.

YBa2Cu3O7 (YBCO) thin films have been fabricated on different textured CeO2-cap layers by pulsed laser deposition (PLD). The texture and critical current density Jc of YBCO thin films have been systematically investigated. Both in-plane and out-of-plane textures of YBCO films and CeO2-cap films were characterized by X-ray diffraction (XRD). And the critical currents of YBCO films were measured by the conventional four-probe method. It was found that the texture and Jc of YBCO films were largely dependent on the texture of CeO2-cap layers under the optimized deposition conditions. With increasing the degree of in-plane and out-of-plane texture of CeO2-cap layers, Jc of YBCO films decreased from 4.23×106 A/cm2 to 0.47×106 A/cm2. The FWHM values of the omega scan rocking curves of YBCO films decreased from 3.71 to 1.84° and the phi scan rocking curves from 6.68 to 4.91° with improvement of CeO2-cap layer texture. Our results indicated that the fabrication of high texture quality of CeO2-cap layer was necessary for the epitaxial growth of high-Jc YBCO films. The high-quality YBCO films which are comparable with those grown on single crystal substrates could be achieved on high textured CeO2-cap layers buffered metal substrates.

YBCO thin films were grown on NiW tapes under continuous moving deposition process. All of YBCO layer, buffer layer, and cap layer were deposited in a compact reel-to-reel pulsed laser deposition system. Since high critical current density is the most important and effective factor to improve performance/price ratio of coated conductor for large scale applications, we focused our research work on enhancing critical current density of YBCO layers on NiW substrates. It was found that superconducting transport properties of YBCO layers were dependent on not only in-plane texture but also surface morphology of buffer layers, especially surface structure and large particles along grain boundary in NiW substrates. High quality YBCO layers with >; 4.0 × 106 A/cm2 (at 77 K, in zero magnetic field) were fabricated on cap layers with nano-scale surface roughness.

Epitaxial growth of CeO2 buffer layers on biaxially textured (001)Ni tapes was studied using pulsed laser deposition. Relationships between microstructure and deposition parameters were systematically studied in order to develop reliable long tape coating processes. It was found that orientation and texture of CeO2 buffer layers were sensitive to deposition parameters. X-ray diffraction analyses showed that CeO2 buffer layers had pure (001) orientation at 860 °C. Under optimized deposition conditions, highly (001) oriented CeO2 buffer layers have been achieved at a high deposition rate of 1.5 nm/s in-plane texture and out-plane texture of CeO2 buffer layers were 4.25 degrees and 5.85 degrees, respectively.

We fabricated CeO2 films using pulsed laser deposition (PLD) for YBa2Cu3O7−δ coated conductors on Ni–5 at.%W alloy substrates and investigated the effect of Ni–5 at.%W tapes on the epitaxial growth and surface morphologies of CeO2 deposited on various substrates at various temperatures ranging from 650 to 770 °C. The texture and microstructure of substrates and CeO2 films were measured by X-ray diffraction (XRD), optical microscope (OM), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). It was found that the texture and microstructure of Ni–5 at.%W substrates, such as Ni(111), grain size, the depth of grain boundary grooves and surface roughness, affected the growth of CeO2 films. Especially, the depth of grain boundary grooves of substrates resulted in high intensity of CeO2(111) peak and high surface roughness of CeO2 films. We also found that high growth temperature effectively reduced the influence of substrate surface roughness on the epitaxial growth of CeO2 films. CeO2 films with high in-plane and out-of-plane alignments (Δφ=5.54°, Δω=3.40°) were obtained under optimum condition.

Yttria-stabilized ZrO2 (YSZ) buffer layers were prepared on Ni-5%W tapes coated with CeO2-seed layers by a pulsed laser deposition (PLD) technique. The influences of oxygen pressure on the structure and surface morphology of YSZ buffer layers for YBCO coated conductors was investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Atomic Force Microscope (AFM) were used to characterize YSZ films. It was found that the structure and surface morphology were sensitive to the oxygen pressure. When the O2 pressure was higher than 1 mTorr, the YSZ film had mixed orientation and rugged surface. When the oxygen pressure was reduced to 0.5 mTorr, YSZ film had the pure (001) orientation. The surface became smooth as the oxygen pressure decreased. However, when the pressure was low to 0.1 mTorr, X-ray diffraction peaks form YSZ (002) were weak and the rough surface appeared again. The results could be explained either by plume stoichiometric changes, gas and ions interaction, or atomic rearrangement on the substrate.

Yttria-stabilized zirconia (YSZ) buffer layers were deposited on CeO2 buffered biaxially textured Ni–W substrate by reel-to-reel pulsed laser deposition (PLD) for the application of YBa2Cu3O7−δ (YBCO) coated conductor and the influence of substrate temperature and laser energy on their crystallinity and microstructure were studied. YSZ thin films were prepared with substrate temperature ranging from 600 to 800 °C and laser energy ranging from 120 to 350 mJ. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin film structure and surface morphology depend on these parameters. It was found that the YSZ films grown at substrate temperature below 600 °C or laser energy above 300 mJ showed amorphous phase, the (0 0 1) preferred orientation and the crystallinity of the YSZ films were improved with increasing the temperature, but the surface roughness increased simultaneously, the SEM images of YSZ films on CeO2/NiW tapes showed surface morphologies without micro-cracks. Based on these results, we developed the epitaxial PLD-YSZ buffer layer process at the tape transfer speed of 3–4 m/h by the reel-to-reel system for 100 m class long YBCO tapes.

Epitaxial CeO2 seed layer and multiple CeO2/YSZ/CeO2 buffer layers were in-situ deposited in a reel to reel pulsed laser deposition chamber on rolling assisted biaxially textured NiW tapes. Epitaxial relationship and surface morphology of each layer were systematically studied by x-ray diffraction (XRD), high resolution scanning electron microscope (SEM) and atomic force microscope (AFM). The in-plane texture of CeO2 cap layer is 6-7 degrees, which was comparable to NiW substrate. During deposition parameter optimization, it was observed that the orientations of YBCO layers were related with individual NiW grains. Although c-axis orientation was the dominant orientation of YBCO films under optimum deposition conditions, a small amount of a-axis orientation was observed in YBCO films. These sun-micro scale a-axis orientated YBCO grains were not uniformly distributed in YBCO films, but only located inside a small percentage of NiW grains. SEM observation showed that grain size of buffer layers was sensitive to deposition parameters. The influence of buffer layer grain size and surface roughness on the epitaxial quality of YBCO layers was investigated.

Epitaxial growth of CeO2 buffer layers on biaxially textured (001) Ni tapes was studied using reel-to-reel pulsed laser deposition. Relationship between microstructure and deposition parameters was systematically studied in order to develop reliable long tape coating processes. Prior to buffer layer deposition, Ni tapes were in situ annealed in forming gas (97% argon + 3% hydrogen) under various pressures and tape speeds to accelerate reel-to-reel annealing processes. It was found that orientation and texture of CeO2 buffer layers were sensitive to deposition parameters. X-ray diffraction analyses showed that CeO2 buffer layers had pure (001) orientation at forming gas pressure of 5 mTorr and 700degC. Under optimized deposition conditions, highly (001) oriented CeO2 buffer layers have been achieved at a high tape speed of 20-50 m/h. In-lane texture of CeO2 buffer layers was 7 degree which was comparable to the value of Ni tapes.

In order to deposit YBCO coated conductor with high critical current densities on rolling assisted biaxially textured Ni-W tapes, this paper has systematically studied the influence of deposition conditions on the orientation, in-plane texture and surface morphology of buffers and superconducting layers. It was found that the crystalline alignment and the in-plane texture of cerium oxide cap-layers were well improved by optimizing deposition parameters. The full width at half maximum of phi-scan x-ray diffraction peaks were reduced from original values of 7-8 degrees to 5-6 degrees. A high critical current density of 4.6×106 A/cm2 has been achieved on optimized buffer layers. This value is comparable with the critical current density of YBCO thin films deposited on single crystalline substrates.

YBCO films were grown on CeO 2 /YSZ/CeO 2 buffered rolling-assisted biaxially textured substrates (RABiTS) by pulsed lased deposition (PLD). CeO 2 cap layer was deposited prior to YBCO growth. CeO 2 cap layers of different thickness were prepared to evaluate the thickness dependence of the YBCO films. The microstructure and surface morphology of the films were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the thickness of the cap layer can remarkably affect the preparation of the subsequent YBCO layer. The possible mechanisms responsible for the dependence of the structure and the preparation of the YBCO films on the thickness of the CeO 2 cap layers are discussed.

GdBa2Cu3O7 − δ (GdBCO) films with different thicknesses from 200 to 2,100 nm are deposited on CeO2/yttria-stabilized zirconia (YSZ)/CeO2-buffered Ni-W substrates by radio-frequency magnetron sputtering. Both the X-ray diffraction and scanning electron microscopy analyses reveal that the a-axis grains appear at the upper layers of the films when the thickness reaches to 1,030 nm. The X-ray photoelectron spectroscopy measurement implies that the oxygen content is insufficient in upper layers beyond 1,030 nm for a thicker film. The Williamson-Hall method is used to observe the variation of film stress with increasing thickness of our films. It is found that the highest residual stresses exist in the thinnest film, while the lowest residual stresses exist in the 1,030-nm-thick film. With further increasing film thickness, the film residual stresses increase again. However, the critical current (I c) of the GdBCO film first shows a nearly linear increase and then shows a more slowly enhancing to a final stagnation as film thickness increases from 200 to 1,030 nm and then to 2,100 nm. It is concluded that the roughness and stress are not the main reasons which cause the slow or no increase in I c. Also, the thickness dependency of GdBa2Cu3O7 − δ films on the I c is attributed to three main factors: a-axis grains, gaps between a-axis grains, and oxygen deficiency for the upper layers of a thick film.