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Abstract: For a-axis oriented and c-axis in-plane aligned YBa2Cu3O7− δ /artificial pinning center (Y123/APC) alternately-layered thin films, effects of the APC materials on the multilayer structures are discussed. Pr123, (Y1− x Pr x )123 and Gd2CuO4(Gd214) were used as APCs. The multilayer structure was observed for Y123/Pr123 films and Y123/Gd214 films. However, some grains are also grown in the Y123/Gd214 film. For the Y123/Pr123 multilayer film, each Pr123 layer act as two-dimensional APCs (2D APCs) in the magnetic field angular dependences of the critical current density. The growth mechanism of the multilayer structure in the Y123/2D APC films is discussed by a transmission electron microscopy and an atomic force microscope. It is found that two conditions are needed to obtain the c-axis correlated pinning effects by 2D APC in the a-axis oriented and c-axis in-plane aligned Y123/APC multilayer films: the same structure as Y123; Y-free APC materials. [Copyright &y& Elsevier]

Abstract: We grew pure ErBa2Cu3O7− δ (ErBCO) films and ErBCO films with BaSnO3 (BSO) doping as artificial pinning centers (APCs) by pulse laser deposition on SrTiO3 substrates, and the effects of oxygen pressure on crystallinity, critical temperature (T C) and microstructure of ErBCO films were investigated. In a previous study, we grew ErBCO films with BaNb2O6 (BNO) by controlling the growth temperature under a constant oxygen pressure of 400mTorr and confirmed the effect of BNO as APCs. We observed the tendency which diameter of nanorods became small and pinning force was strong at lower growth temperature. However, crystallinity and T C of ErBCO films degraded at low growth temperature. So, it is very important to improve crystallinity and T C by a novel method. In this study, we focused on oxygen pressure, and aimed at improvement of crystallinity and T C by controlling oxygen pressure. [Copyright &y& Elsevier]

Abstract: We fabricated a BaSnO3-doped NdBa2Cu3O7− δ film on a MgO substrate by a pulsed laser deposition method. We confirmed 00l reflections of NdBa2Cu3O7− δ film in X-ray diffraction. In the cross-sectional transmission electron microscopy observation of the film, the presence of nanorods with 20nm with average diameter is confirmed from bright-field images. We confirmed these nanorods contained tin (Sn) by EDS elemental maps. The crystal structure of the nanorod was determined to be cubic perovskite from its selected area electron diffraction pattern. Using the selected area electron diffraction patterns, the lattice constant of the nanorods in the NdBa2Cu3O7− δ film was calculated to be 0.415nm which was in good agreement with the lattice constant of BaSnO3 of 0.412nm. [Copyright &y& Elsevier]

Abstract: We report effects of growth temperature on superconducting properties and microstructure of ErBa2Cu3O7− δ (ErBCO) films with BaNb2O6 (BNO)-doping grown by pulse laser deposition (PLD) on SrTiO3 (STO) substrates. The BNO was introduced into the ErBCO films as artificial pinning centers. X-ray diffraction analysis indicated the high orientation of both c-axis and in-plane for the obtained BNO-doped ErBCO (BNO+ErBCO) films. Ba(Er0.5Nb0.5)O3 (BENO) nanorods were observed clearly in transmission electron microscopy (TEM) images of the BNO+ErBCO films. The BENO nanorod was thinner with decreasing the growth temperature. The BNO+ErBCO films showed higher critical current density (J C) than that of a pure ErBCO film in a magnetic field (H) in H∥c-axis, indicating that BENO nanorods played as c-axis correlated pinning centers. Furthermore, we found a tendency that J C of the BNO+ErBCO films were enhanced with decreasing the growth temperature. Consequently, the pinning effect of the introduced BENO was controlled by the optimization of growth condition such as growth temperature. [Copyright &y& Elsevier]

Abstract: We report superconducting properties and microstructures of a ErBa2Cu3O7−δ (ErBCO) film with 1.5wt% BaNb2O6 (BNO) grown by pulse laser deposition (PLD) on a SrTiO3 (STO) substrate. The BNO was introduced into the ErBCO film as an artificial pinning center. Nano-rods originated in the BNO-doping and some particulate defects were clearly observed in transmission electron microscopy (TEM) images of the ErBCO film. The ErBCO film with BNO-doping (BNO+ErBCO) had almost the same critical temperature (T C) as that of a pure ErBCO film. On the other hand, the BNO+ErBCO film showed less critical current density (J C) than that of the pure ErBCO film. The angular peaks for H∥c-axis on J C–B–θ curves were not confirmed under all the measured external magnetic fields. X-ray diffraction analysis indicated the high orientation to the both c-axis and in-plane for the obtained film. However, the low surface flatness was confirmed by the TEM and atomic force microscopy (AFM) observation. [Copyright &y& Elsevier]

Abstract: A multilayer alternately stacked a-axis oriented YBa2Cu3O7−δ and PrBa2Cu3O7−δ (Y123/Pr123 multilayer) has been grown on a SrLaGaO4 substrate with a Gd2CuO4 buffer layer by pulsed laser deposition. We used an Y123 target that contains a Pr123 sector for obtaining the Y123/Pr123 multilayer. The multilayer structure of the obtained film was confirmed by a transmission electron microscope. In magnetic field (B) angular dependences of critical current density (J C) (J C–B–θ curves), J C peaks were observed at B∥a-axis and B∥c-axis of the Y123/Pr123 multilayer. Peaks at B∥c-axis are absent in J C–B–θ curves of pure a-axis oriented Y123 films. Therefore, peaks at B∥c-axis in J C–B–θ curves of the Y123/Pr123 multilayer are attributed to Pr123 layers. This result indicates that the Y123/Pr123 multilayer has c-axis-correlated pinning centers. Consequently, it is concluded that Pr123 layers work as two-dimensional artificial pinning centers with the current direction along the b-axis. [Copyright &y& Elsevier]

Abstract: We fabricated an ErBa2Cu3O7−δ (ErBCO) thin film with BaZrO3 (BZO) doping (BZO+ErBCO) on a SrTiO3 (STO) substrate by a pulsed laser deposition (PLD) method using a novel target which consists of two parts. One is ErBCO for a superconducting phase, the other is rectangular shaped BZO for pinning centers. From an X-ray diffraction (XRD) pattern, the ErBCO film was c-axis oriented and in-plane aligned on the STO substrate. Microstructures of the BZO+ErBCO film were observed by a transmission electron microscope (TEM). In the TEM image, nano-particles of BZO were observed in the film, not nano-rods. This result means that the novel target enables to dope BZO nano-particles into the film without any target changing. From the TEM image and thickness of the sample, a volume percentage of BZO nano-particles is calculated to be 7.3vol%. It is almost the same to the calculated value from the percentage of laser irradiating area. [Copyright &y& Elsevier]

Abstract: ErBa2Cu3O y films including BaZrO3 are deposited using three types of targets by PLD to realize the self-oriented growth of BaZrO3 nanorods. Microstructures of the obtained films are observed using a transmission electron microscope (TEM). On the basis of the cross-sectional TEM images, the growth mechanism of the BaZrO3 nanorods is discussed. When about a half of BaZrO3-monolayer is added, it is found that the BaZrO3 is not widely segregated to BaZrO3 region and no BaZrO3 region on the ErBa2Cu3O y surface but the BaZrO3 is homogeneously distributed with approximately 10nm periods on the ErBa2Cu3O y surface. As a result, the crystal stress due to the differences of crystal length between the ErBa2Cu3O y and BaZrO3 are introduced for every 10nm to the films. This behavior is probably the origin of the self-oriented growth of BaZrO3 nanorods. [Copyright &y& Elsevier]

Abstract: Surface resistances (R S) have been measured for EuBa2Cu3O7−δ (EuBCO) films grown in an ozone atmosphere. We grew BaZrO3 dispersed EuBCO films with artificial pinning centers (APCs) in an ozone atmosphere. We have investigated the effects of BaZrO3 dispersion into EuBCO films. The EuBCO films were grown using a pulsed laser deposition (PLD) in an ozone atmosphere on (100) SrTiO3 substrates. We use a pure EuBCO target and an EuBCO+1.0wt% BaZrO3 target. By BaZrO3 dispersion into EuBCO films, the crystallinity of BaZrO3 dispersed EuBCO films was poorer than that of pure EuBCO films. BaZrO3 dispersion into EuBCO films did not improve their superconducting characteristics. Then we evaluated microstructure by using transmission electron microscopy (TEM). We observed nano-rods in BaZrO3 dispersed EuBCO films. However, we did not observe nano-rods in BaZrO3 dispersed EuBCO films grown in an oxygen atmosphere. The differences between an ozone and an oxygen atmosphere influence on nano-rod forming. We found that the nano-rod size is important and is strongly related to not only RE (RE: Rare Earth) ion radii but also growth conditions of films. [Copyright &y& Elsevier]

Abstract: Effects of artificial pinning centers (APCs) into ErBa2Cu3O7−δ films are discussed. The APCs used in this paper is BaZrO3 and Zn which are mixed into ErBa2Cu3O7−δ ceramic targets. The targets with various contents of APCs are ablated and films are grown on substrates with the APCs. X-ray diffraction patterns show there are no other phases than ErBa2Cu3O7−δ and APCs. Transmission electron microscopy (TEM) shows the BaZrO3 APSs grow along the c-axis of the films. The introduction of APCs decreases surface resistance (R S) of ErBa2Cu3O7−δ films and increases critical current density (J C) of the films. R S measurements revealed that the ErBa2Cu3O7−δ films with APCs showed a lower R S than that of the ErBa2Cu3O7−δ films without APCs. [Copyright &y& Elsevier]

Abstract: The Zn-doped ErBa2Cu3O7−δ thin films were prepared by a pulse laser deposition (PLD) on a SrTiO3, which is a lattice, matched substrate. The various contents of the Zn-doped ErBa2Cu3O7−δ ceramics were used as the targets. All the films were grown at 750°C under an oxygen pressure of 400mTorr. From the X-ray diffraction (XRD) patterns, only the 00 l reflections were observed. Surface resistance (R S) measurement revealed that the ErBa2(Cu0.9Zn0.1)3O7−δ films showed a superconducting transition temperature (T C) below 70K. The R S value of the ErBa2(Cu0.997Zn0.003)3O7−δ films and that of the ErBa2(Cu0.995Zn0.005)3O7−δ films was lower than that of the ErBa2Cu3O7−δ films for wide temperature region of 10–90K. From the observation of the atomic force microscopy (AFM), a lot of pores were observed in the surface of the Zn-doped ErBa2Cu3O7−δ films, which showed a low R S. [Copyright &y& Elsevier]

Abstract: We have designed and fabricated a microwave sensing system integrated with superconducting devices which can detect motion for crime prevention and security purposes. The system consists of a transmitting antenna, a receiving antenna, a power divider as a directional coupler, and a mixer. The antennas and the directional coupler were fabricated using 50-nm thick YBa2Cu3O7−δ (YBCO) thin films. A superconducting antenna with a resonant frequency of 10.525GHz and a superconducting directional coupler were designed and fabricated for the system. A Schottky barrier diode was used as a mixer. These devices were integrated and their operation as a sensor was examined. Comparisons of the output voltage of the IF signal amplifier showed that the superconducting integrated sensor system was superior to the normal conductor sensor. [Copyright &y& Elsevier]

Abstract: We have investigated the dependence of the crystallinity and the superconducting characteristics in the EuBa2Cu3O7−δ (EuBCO) thin films on oxygen content. The EuBCO films were grown using a pulsed laser deposition (PLD) under an oxygen and an ozone atmosphere on (100) SrTiO3 substrates. The c-axis length of as-grown EuBCO films under the oxygen atmosphere was longer than that of the bulk. The c-axis length of in situ annealed EuBCO films was shortened as compared with the as-grown EuBCO films. Additionally, the surface resistance (R s) of the in situ 3 and 6h annealed EuBCO films was lower than that of as-grown EuBCO films. However, the surface resistance of in situ annealed more than 24h EuBCO films was not lower than that of in situ 6h EuBCO films. The c-axis length of the as-grown EuBCO films grown under an ozone atmosphere showed 1.170nm. It must be noted that the lowest surface resistance of EuBCO films was obtained by EuBCO films grown under the ozone atmosphere without any in situ annealing. We found that the growth of EuBCO films under the ozone atmosphere was good to dope oxygen in the films. [Copyright &y& Elsevier]

Abstract: We have grown a-axis oriented ErBa2Cu3O7−δ (ErBCO) films. Crystallinity of ErBCO films grown on Gd2CuO4 (GCO) buffer layers are investigated at various growth temperatures, in order to find a condition to fabricate a-axis oriented ErBCO films. a-Axis oriented ErBCO films are also grown at a high growth substrate temperature by using YBa2Cu3O7−δ (YBCO)/GCO double buffer layers. We have successfully fabricated a-axis oriented ErBCO films with the GCO buffer layer by optimizing the substrate temperature during growth. Furthermore, we optimized growth temperatures for a-axis oriented ErBCO films are increased by using the YBCO/GCO buffer layer. [Copyright &y& Elsevier]

Abstract: ErBa2Cu3O7−δ thin films with BaZrO3 dispersion pinning centers for high J C applications were grown using ErBa2Cu3O7−δ targets with various BaZrO3 contents. The J C improvement at high applied magnetic fields was observed for the ErBa2Cu3O7−δ films with BaZrO3 dispersion pinning centers. From the cross-sectional transmission electron microscope images of the ErBa2Cu3O7−δ films with BaZrO3 dispersion pinning centers, we believe that the BaZrO3 nano-particles in ErBa2Cu3O7−δ films play a role of pinning centers. Increase of the amount of BaZrO3 nano-particles in ErBa2Cu3O7−δ films induced drastic reduction of the surface resistance (R S). This result suggests that the ErBa2Cu3O7−δ films with BaZrO3 nano-particles can be applied to high power microwave emitting devices. [Copyright &y& Elsevier]

Abstract: We report the effects of oxygen post-annealing on critical current properties and normal state resistivities in ErBa2Cu3O y /SrTiO3(Er123/STO) thin films fabricated in the substrate temperature range from 720°C to 780°C by pulsed laser deposition (PLD). Interestingly, for films fabricated below 760°C, the critical current density (J c) increased by oxygen post-annealing process from 0.3–0.6×106 Acm−2 to the order of 106 Acm−2 for the as-deposited films despite critical temperatures (T c) of ∼90K for both annealed and as-deposited films. In the 780°C-deposited film, J c was not obviously enhanced. X-ray diffraction and measurement of normal state resistivities revealed that the PLD-Er123/STO films showed high-quality crystallographic and electrical properties in films deposited below 760°C. In high temperature resistivity measurements, the resistivity reduced with annealing time and showed a systematic change with changing oxygen partial pressure. These results strongly suggest that oxygen post-annealing is indispensable for improving J c in 123 films fabricated through a non-equilibrium process such as the PLD method even though the as-deposited films show a T c value of ∼90K. [Copyright &y& Elsevier]

Abstract: Microstructure deformation has been investigated for EuBa2Cu3O x films associated with orthorhombic–tetragonal transition during cooling in an oxygen atmosphere. EuBa2Cu3O x films have been grown by a pulsed laser deposition technique under 1000mTorr oxygen pressure and 800°C substrate temperature. After the growth, the films are cooled to 400°C and annealed in one atom oxygen pressure for 0–110h. The preferred orientation of the films is characterized by X-ray diffraction and ϕ-scan X-ray diffraction. Microstructures and lattice images of the EuBa2Cu3O x films are observed by a transmission electron microscope. All of the obtained EuBa2Cu3O x films are c-axis oriented. The ϕ-scan X-ray diffraction revealed that films without any 500°C annealing have a tetragonal structure. However, more than 3h annealed films are partly orthorhombic from the peak separation in the ϕ-scan. The angle between the two peaks is about 0.8°. We estimate the a-axis length/b-axis length ratio (orthorhombicity) from the angle between the separated peaks to be 0.866°. It agrees with the a-axis length/b-axis length ratio of well oxidized EuBa2Cu3O x bulk materials. [Copyright &y& Elsevier]

We report oxygen post-annealing effects of superconducting properties on ErBa2Cu3Oy thin films fabricated by a pulsed laser deposition (PLD) method. Critical current densities were dramatically enhanced by an oxygen post-annealing process at temperature range of 350–500 °C in comparison with that of the as-deposited film (∼0.3 MA/cm2). Even in REBa2Cu3Oy films grown by a non-equilibrium process such as the PLD method, the oxygen post-annealing process is crucially effective for enhancement of critical current properties, which is suggesting that the oxygen annealing is a practical process for improvement of critical current of PLD-REBa2Cu3Oy coated conductors. [Copyright &y& Elsevier]

Recently solid phase epitaxial YBa2Cu3O7-δ films such as metal organic deposition using trifluoroacetate (TFA-MOD) technique, chemical solution-based coating pyrolysis, and BaF2 ex situ post reaction process have been improving their crystalline quality. In order to grow thick films, larger thermal expansion coefficient substrates than that of YBCO are preferable. From the viewpoint of thermal expansion coefficient, MgO is a promising substrate. However, it is difficult for solid phase epitaxial YBa2Cu3O7-δ films to grow directly on the MgO substrate, because fluorine reacts with Mg in the substrate. Therefore we evaluate buffer layer materials to protect MgO substrates against fluorine. Buffer layer are grown by pulsed laser deposition at around 730 °C on polished MgO substrates. Thin CeO2 buffer layers are difficult to grow directly on the MgO substrates. However, CeO2-capped double buffer layers grow epitaxially on MgO substrates. The examined materials for double buffer layers are CeO2/SrSnO3, CeO2/BaSnO3 and CeO2/BaZrO3. Crystallinity of the buffer layers are characterized by X-ray diffraction (XRD) θ–2θ-scans and XRD φ-scans. From XRD θ–2θ-scans patterns crystallinity of the CeO2 on BaSnO3 is higher than those of the others. From XRD φ-scans patterns, all of these buffer layers were the perfect in-plane alignment. The intensity of CeO2 film on BaSnO3 was the highest in all films. Surface morphologies are observed by AFM. From AFM observation, it was demonstrated that the surface of CeO2 film on BaSnO3 was smooth. We confirmed that CeO2 film grown on a BaSnO3 buffer layer crystallized better than others. [Copyright &y& Elsevier]

ErBa2Cu3O7-δ thin films are grown by pulsed laser deposition (PLD). Using a SrTiO3 as a lattice matched substrate. In the film growth, the substrate temperature is varied from 720 to 780 °C. From X-ray diffraction (XRD) patterns, only the 0 0 l reflections from the ErBa2Cu3O7-δ films are observed. The average of the c-axis length of the other films is 11.6875 Å. ErBa2Cu3O7-δ film grown at 735 °C is excellent in the crystallinity, while the intensity of 0 0 l peaks of the film grown at more than 780 °C obviously weakened. The zero resistance Tc is 90.5 K. Superconducting transition width is 1.5 K. Large and flat grains are observed by atomic force microscopy (AFM) at the surface of the film. From the scanning electron microscope (SEM) image, we confirmed some grains with the size of approximately 200 nm in diameter on the ErBa2Cu3O7-δ thin film. We observe the interface of ErBa2Cu3O7-δ and substrate clearly by transmission electron microscopy (TEM) measurements. [Copyright &y& Elsevier]

We discuss selective preferred orientation control of YBa2Cu3O7-δ films on a substrate. c-Axis oriented YBa2Cu3O7-δ films grow on the region without buffer layer. On the other hand a-axis oriented YBa2Cu3O7-δ films grow on the region with the buffer layer in spite of the same growth temperature and oxygen pressure. Crystalline orientation, surface morphology and transport properties along the b-axis of the a-axis oriented films will be also discussed. [Copyright &y& Elsevier]

A grain size control technology will be described. YBa2Cu3O7−δ thin films are grown by a pulsed laser deposition method in 400 mTorr oxygen atmosphere. The films are grown by a self-template method with various self-template growth temperatures. However the temperature of the main YBa2Cu3O7−δ layer was fixed. Grain size of YBa2Cu3O7−δ thin films on MgO substrates are observed by atomic force microscope. Mean diameter of grains are calculated by the number of grains in scanned area of 1×1 μm2. The mean diameters are 2.49×102, 2.89×102, 4.047×102 and 4.192×102 nm for films with an initial layer growth temperature of 670, 690, 714 and 730 °C, respectively. Grain size is found to depend on the initial growth stage of the YBa2Cu3O7−δ thin film growth. These grain sizes have a strong relationship with the inverse of substrate temperature indicating thermally excited migration of YBa2Cu3O7−δ nuclei. It is also clarified that migration length of YBa2Cu3O7−δ nucleus is longer on an YBa2Cu3O7−δ films than on MgO substrates. [Copyright &y& Elsevier]

Abstract: BaSnO3 (BSO)-doped ErBa2Cu3O7−δ (ErBCO) films are grown by a pulsed laser deposition (PLD) method on SrTiO3 (STO) substrates for realizing high J C in a magnetic field. ErBCO ceramics with BSO-contents of 0–8.0wt% are used as targets. From XRD analyses of the obtained films, 00 l reflections of ErBCO are observed, indicating that the films are c-axis oriented. BSO grew in a shape of nanorod in all ErBCO films. The BSO-doped ErBCO films showed higher J C than non-doped ErBCO films in magnetic fields, suggesting that BSO nanorods plays a role of pinning centers. On the other hand, the J C properties depended strongly on the concentration of BSO-doped in ErBCO films; a 4wt% BSO-doped ErBCO film showed lower J C than that of a 2wt% BSO-doped film. These BSO-content dependences on J C for ErBCO films were understood as poor alignment of ErBCO crystal grains caused by BSO doping. We believe that the optimized BSO doping content into ErBCO films for high J C is around 2wt% among the obtained films. [Copyright &y& Elsevier]

Abstract: Electrical transport properties are discussed for YBa2Cu3O7− δ 123) films with 2-dimensional artificial pinning centers (2-D APCs). An Y123/Pr123 multilayer film with T C0 of ∼80K was successfully grown on a SrLaGaO4 substrate. In the Y123/Pr123 multilayer film, the a-axis oriented Y123 and Pr123 were stacked alternately on the substrate. J C–θ curves in magnetic fields at 60K showed a peak at B //c, suggesting that the Y123/Pr123 multilayer films have c-axis correlated pinning centers. The magnetic field dependence of the J C( B //c)/ J C( B //a) showed a maximum around the calculated matching field of the Y123/Pr123 multilayer film. The J C( B //c)/ J C( B //a) decreased above the matching field. [Copyright &y& Elsevier]

Abstract: BaWO4 (BWO) doped ErBa2Cu3O7−δ (Er-123) (BWO+Er-123) films are fabricated and their superconducting properties are evaluated. We discuss the effect of BWO doping into Er-123 films on their crystallinity and superconducting properties. The grown BWO+Er-123 films were in-plane aligned and c-axis oriented. We characterize in-plane crystallinity of the films by XRD in-plane rotation measurement (φ-scan). The full width at a half maximum of the φ-scan pattern (δφ) of the grown BWO+Er-123 films became wider as increasing BWO doping. The critical temperature (T C0) of 2.0wt% BWO+Er-123 films was about 90.5K. From this result, it was confirmed that the BWO+Er-123 films had as high T C as pure Er-123 films. Surface resistance (R S) of the BWO+Er-123 films was degraded comparing to that of a pure Er-123 film. The relationships between critical current density (J C) and applied magnetic field (J C–B) and the magnetic field angular dependence of J C of the grown 2.0wt% BWO+Er-123 film were evaluated at 77K. As a result, it is confirmed that the J C of the Er-123 films in magnetic fields decreased by the BWO doping comparing to that of the pure Er-123 film. However, it was also confirmed that the 2.0wt% BWO+Er-123 film had weak pining centers along the c-axis of Er-123 films. From the result of a cross-sectional transmission electron microscope (TEM) image, some rod structures were observed in the 2.0wt% BWO+Er-123 films. The diameter of the rod was about 20nm. These rods grew along the c-axis of Er-123 films from the substrate to the surface of the film. [Copyright &y& Elsevier]

Abstract: We have improved surface resistance (R S) properties of ErBa2Cu3O7−δ (ErBCO) films by using BaTiO3 (BTO) doping (BTO+ErBCO). The as-grown BTO+ErBCO films did not have enough carriers. We solve this problem by using O3 +O2 as background gas during the growth of BTO+ErBCO films. Then, O3 +O2 gas is useful to grow BTO+ErBCO films with superior superconducting properties. The R S of a 2wt.%BTO+ErBCO film is the lowest in BTO+ErBCO films grown in this study. This value is equal to that of a 1.5wt.%BZO+ErBCO film. The microstructures of the 2wt.%BTO+ErBCO film are observed by transmission electron microscopy (TEM). In the image, the BTO+ErBCO films did not have the same nanorods as observed in the BZO+ErBCO films against our expectation. However, precipitates that the BZO+ErBCO films do not have, are observed. [Copyright &y& Elsevier]

YBa2Cu3O7-x (YBCO) is prepared by low-oxygen-pressure annealing of precursor films which are deposited from Y, BaF2 and Cu sources at room temperature. In the annealing process, pure oxygen gas is introduced into the reaction chamber. The other gases, for example, water vapor or nitrogen gas, are not intentionally introduced. We previously reported that it is difficult to control the in-plane alignment YBCO films on MgO substrates. Therefore, a single cap layer (BaSnO3) or double cap layers (CeO2/BaSnO3) are deposited on the MgO substrate. Subsequently, the YBCO films are prepared on the cap-layer-buffered MgO substrates. We evaluated the crystallinity and the film growth of the YBCO films on single-cap-layer-buffered and double-cap-layer-buffered MgO substrates. [Copyright &y& Elsevier]

We have systematically investigated dependence of crystalline orientation on film thickness of sputtered YBa2Cu3O7−x (YBCO) on an MgO substrate by the X-ray diffraction (XRD) method, the φ diffraction method and atomic force microscope (AFM). From examination of crystalline orientation by XRD method and in-plane orientation by the φ diffraction method, for thinner film below about 500 nm, the YBCO film is oriented with the c-axis perpendicular to the MgO substrate surface. For thicker film above about 500 nm, the c-axis oriented grains in the YBCO film vanish entirely and the a-axis oriented grains are formed. The rectangular images of a-axis oriented grains are also observed on the surface by AFM. We found that the crystalline orientation change drastically from c-axis oriented films to a-axis oriented films with increasing film thickness. [Copyright &y& Elsevier]

We have investigated crystallinity of YBCO films on an MgO substrate using an amorphous buffer layer. The evaluated films are obtained as follows: an amorphous YBCO buffer layer is deposited on the MgO substrate at a low temperature (200 °C); and then, an amorphous buffer layer is crystallized by the thermal annealing at a high temperature from 910 to 1030 °C; finally, main YBCO film is grown on the crystalline YBCO buffer layer over the MgO substrate. A significant improvement in the crystalline quality of the YBCO films was achieved, when amorphous buffer layers of 100 nm in thickness were crystallized by annealing temperature 950 °C and then annealing is continued for 1 h in air atmosphere. We confirmed that YBCO films grown on a well-crystallized buffer layer had better crystallinity than ones on bare MgO substrate, which has substantially large lattice mismatch. [Copyright &y& Elsevier]

Abstract: Critical current density (J C) of REBa2Cu3O7− δ (REBCO) films deteriorates in a magnetic field. One of the methods to solve the J C deterioration is to introduce artificial pinning centers (APCs) such as nanorods into the REBCO films. When many nanorods with a small diameter grew up than less rods with large diameter in REBCO films, the nanorod are considered to act as APCs. Therefore, we focused on controlling the rod diameter in order to realize the higher number density of nanorods in REBCO films. BaNb2O6 (BNO) was introduced in ErBCO films. In order to decrease the diameter of nanorods, we think it is necessary to control migration length of Nb atoms at the film surface of the ErBCO. As a result, it was observed in TEM image that diameter of nanorods was changed by varying substrate temperature and decreased with decreasing the substrate temperature. [Copyright &y& Elsevier]

Abstract: We report vortex-Bose-glass-like irreversibility lines (IL) depending on both growth temperature and nominal content of a nanorod material in Er–Ba–Cu–O films containing nanorods. The IL was expanded to higher magnetic fields with decreasing growth temperature , while decreased. Our findings indicate that in the production process of coated conductors containing nanorods is an important determination factor of critical current performance under high magnetic fields. [ABSTRACT FROM AUTHOR]

Abstract: Fe(Te,S) has a tetragonal PbO type structure with of around 10K, which is the simplest structure among iron-based superconductors. We deposited Fe(Te,S) thin films by PLD method using the second harmonic light of Nd:YAG pulsed laser (wavelength=532nm) in the range of a deposition rate from 14pm/s to 56pm/s on MgO, SrTiO3 and LaAlO3 substrates. We obtained the thin films showed the c-axis orientation normal to the film surface and in-plane alignment. The film deposited on LaAlO3 showed of 9.3K. and increased to 11K and 6.6K respectively by the excess adding Te to the stoichiometric target. was higher than that of a Fe(Te,S) bulk. The lattice constant of the films was strongly related to . has local maximum value at 6.195Å of c-axis length. [Copyright &y& Elsevier]

Abstract: We investigated the relationship between the intrinsic surface resistance () and critical current density (J c) of YBa2Cu3Oy (YBCO) film thinner than the penetration depth (λ L). The measured YBCO films were deposited on CeO2-buffered r-cut Al2O3 substrates by the pulsed laser deposition method. The thicknesses of these films were 300, 200, and 100nm, respectively. The means the surface resistance of YBCO film removing the loss by the impedance of the substrates. The effective surface resistance () including the impedance of the substrate and the J c of each YBCO film were measured using the dielectric resonator method at 21.8GHz and the inductive method. We calculated by using phenomenological expressions and the value. The values of each YBCO film were almost the same in the measured temperature region. As a result, we found that was in inverse proportion to the J c of YBCO film thinner than λ L. [ABSTRACT FROM AUTHOR]

Abstract: We report the microstructure change of BaSnO3 (BSO)–YBa2Cu3O7− x (YBCO) thin film system grown on SrTiO3 single crystal substrates by pulsed laser deposition with using the “surface-modified-target” and “mixture-target” methods. Although it was confirmed that the thick BSO nanorods incorporated to YBCO films act as strong artificial pinning centers, the formation mechanism of the nanorods is still unclear. The purpose of this work is to extend the structural investigation to higher contents of BSO (up to 71vol.%) in order to enlighten the relationship among interfacial energy, morphology and pinning performance in binary BSO–YBCO films. [ABSTRACT FROM AUTHOR]

Abstract: To clarify the growth mechanism of faceted REBa2Cu3O7− δ (RE123, RE=Sm, Y) crystals, the growth process of the crystals was observed in situ by using a high temperature microscope. The growth rate of each faceted interface of a crystal growing from the liquid+211 phases under an undercooling was obtained from the relationship between the position of each interface and growth time. It was observed that some of the faceted interfaces of a growing crystal stopped growing after a period of time, while other interfaces continued to grow with a growth rate approximated by a function of the undercooling. The above stoppage of the growth was observed in situ for the first time, and this fact could give powerful support to the mechanism for a similar phenomenon in REBCO films which were fabricated by the trifluoroacetates metal organic deposition method: growing microstructures of RE123 crystals in the film were revealed by transmission electron microscopy (TEM) for quenched specimens. Some very thin a-axis grains were formed by a change in c-axis growth rate. Furthermore, we showed the above growth and stop phenomena of faceted interfaces of REBCO crystal grains using numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract: The temperature T variation of the normalized magnetization relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster relaxation at low T appearing in standard magnetization relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the low-T range is also evidenced. The collective (elastic) creep regime is generated by the T dependent macroscopic currents induced in the sample during standard magnetization measurements. [ABSTRACT FROM AUTHOR]

Abstract: Fe–Te–S thin films deposited by pulsed laser deposition at 400°C on SrTiO3 (100) and MgO (100) single crystals showed epitaxy and 4-fold symmetry. Films deposited on both substrates reached zero resistance condition ( on STO and 5.37K on MgO) and presented large upper critical field (Bc 2(0) = 61.1T on STO and 74.2T for MgO using 90% of the normal state resistance and Werthamer–Helfand–Hohenberg model), indicating that the coherence length ξ 0 of the present films is very short (ξ 0 =2.3nm on STO and 2.1nm on MgO). [ABSTRACT FROM AUTHOR]

Abstract: We were successful for three-dimensional imaging of microstructures in YBa2Cu3O7− y (Y123) films fabricated by metal organic deposition using trifluoroacetates (TFA-MOD) method. We have reported previously, that a transmission electron microscopy (TEM) analysis clarified microstructures such as Y123 crystal grains and pores in the Y123 films. In order to derive important parameters for enhancement of superconducting properties of the Y123 films, quantitative analyses of those microstructures are required. Then, control of both pores and a-axis oriented grains distribution in the Y123 films are important. However, general TEM images provide only a two-dimensional projection of a three-dimensional object. An electron tomography is an effective technique for three-dimensional structure analysis of various materials. Cross-sectional view specimen for the three-dimensional electron tomography was prepared by focused ion-beam milling equipped with micro-sampling system. A scanning transmission electron microscopy – annular dark field technique was used for the present three-dimensional electron tomography. For the cross-sectional specimen of fired Y123 films, three-dimensional shapes and distributions of both pores and unreacted phases were observed in reconstructed images. Also, morphologies of the Y123 film surface were clearly seen. [Copyright &y& Elsevier]

Abstract: To improve J C properties in a magnetic field (J C–B) of YBa2Cu3O7− δ (YBCO) films by a TFA-MOD (trifluoroacetates metal organic deposition) method, we fabricated YBCO films with SnO2-doping as artificial pinning centers and investigated the superconducting properties and the crystalline structures. TFA-MOD is expected as a cost-effective method with a non-vacuum system to fabricate YBCO films with high superconducting properties. However, YBCO films have problems that J C decreases in a magnetic field (B). In this study, the TFA solutions with SnO2 for pinning centers were used as starting materials. In the transmission electron microscope image, existence of second phase particles with size of 20–30nm has been observed in the YBCO film. These nano-particles contained Sn-element and distributed randomly in the film. The J C/J C (self field) values of the SnO2-doped YBCO films were enhanced in all magnetic field angles. Therefore it is considered that 3D pinning centers of Sn-compounds were introduced into YBCO film. [Copyright &y& Elsevier]

Abstract: In REBa2Cu3O y (RE123) films with BaZrO3 (BZO), the columnar shaped BZO precipitates, called nano-rods, are formed as the c-axis-correlated pinning centers. In order to understand the vortex pinning properties of RE123 films with BZO nano-rods, we measured the resistivity ρ and critical current density J c of three different films, i.e. the Er123 films with 0, 1.5 and 3.5wt% BZO prepared by pulsed laser deposition. We found that the peak related to the c-axis-correlated pinning in the angular dependence of J c became large in a low field region but small in a high magnetic field with increasing BZO concentration. In addition, the irreversibility field at B||c-axis increased also with increasing BZO concentration, although the dip in the angular dependence of ρ and the peak of the J c at B||c-axis decreased in the high magnetic field near the irreversible field. It is suggested that the BZO addition is effective to the enhancement of J c in a low field region as well as the improvement of the irreversibility field. However, we have to consider the c-axis-correlated pinning by the edge dislocations as well as the nano-rods in order to understand it in a high field region. [Copyright &y& Elsevier]

Abstract: BaZrO3 (BZO) yields a dramatic enhancement in flux pinning properties in REBa2Cu3O y films due to the formation of self-organized BZO nanorods. In this study, we fabricated BZO-doped (Nd,Eu,Gd)Ba2Cu3O y (NEG) films by various film growth processes, such as low temperature growth (LTG) and modified LTG (mLTG), and we compared the superconducting properties and the microstructures of BZO within the NEG films. From measurements of magnetic field angular dependence of J c, even though both LTG and mLTG films showed high J c peaks at the B‖c-axis, the J c peak in the mLTG film was higher than that in the LTG film. This difference is attributed to a difference in the configuration of BZO in the films. In order to clarify the configuration of BZO within the films, we evaluated X-ray reciprocal space maps (RSM) of the films. The RSM including BZO 103, NEG 108 and NEG 109 reflections exhibited epitaxial relationship of (001)[100] BZO‖(001)[100] NEG. We also observed tetragonally deformed BZO. [Copyright &y& Elsevier]

Abstract: In order to improve a critical current density (J c) under applied magnetic fields, an addition of BaMO3 (BMO; M=Zr, Sn) nanorods into REBa2Cu3O y (REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO3 (BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm1+ x Ba2− x Cu3O y (Sm+BZO) film by using modified Vapor–Liquid–Solid (VLS) technique (VLS-Sm+BZO/i). The in-field J c of the VLS-Sm+BZO/i film showed 4.5 times higher than that of Sm+BZO film fabricated by conventional pulsed laser deposition method (PLD-Sm+BZO) at B =4T and the J c–B–θ curves of the VLS-Sm+BZO/i film was higher than that of the PLD-Sm+BZO film around the applied field angle of 40° against the c-axis of the SmBCO. From a TEM observation, we found that the BZO nanorods of VLS-Sm+BZO/i film grew discontinuously along the c-axis of the SmBCO. [Copyright &y& Elsevier]

Abstract: We investigated the flux pinning properties of nano-rods comprised of BaZrO3 and BaSnO3 in REBa2Cu3O7−δ (REBCO, RE: rare earth elements) thin films. The doping amounts of BaZrO3 in YBa2Cu3O7−δ thin films and BaSnO3 in ErBa2Cu3O7−δ thin films were varied with 0–3.5 wt% and 2.0–4.0 wt%, respectively. The in-field critical current density of 1.5 wt%-BaZrO3-doped YBa2Cu3O7−δ film was higher than those of any other samples measured in this study. The α values in the relation of J c–B −α are 0.2–0.3 for the BaZrO3- and BaSnO3-doped films. This fact shows the introduction of nano-rods is effective for the less magnetic field dependence of J c. As one of the important results, it was found that the introduction of nano-rods caused the peak or kink in the magnetic field dependence of the pinning parameter m which was derived from the scaling of current–voltage characteristics. This phenomenon is the sign of the flux pinning due to the one-dimensional pinning centers. The peak fields of the BaSnO3-doped films were slightly lower than those of the BaZrO3-doped films, though the dope levels of the BaSnO3-doped films were higher. This suggests that the diameter of BaSnO3 nano-rods is larger than that of BaZrO3 ones. [Copyright &y& Elsevier]

Abstract: For an enhancement of J c under applied magnetic fields, introducing BaZrO3 (BZO) into REBa2Cu3O y (REBCO) is effective. However, there have been few reports on the comparison of configurational effect of BZO on the crystallinity, superconducting properties and microstructures in REBCO films. In this study, we fabricated 2 vol.% BZO-doped Sm1+ x Ba2− x Cu3O y (SmBCO) films by pulsed laser deposition with two different methods during deposition; using BZO-doped SmBCO target (BZO-mixed SmBCO), and alternating SmBCO and BZO targets (BZO-layered SmBCO). The angular dependence of J c (77K, B =1T) in the BZO-mixed SmBCO film exhibited strong peak in the direction parallel to the c-axis, while the J c of the BZO-layered SmBCO film was enhanced in the whole field angle range. From a microstructure analysis, nanosized BZO-particles were observed in the BZO-layered SmBCO film and they acted as isotropic pinning centers. [Copyright &y& Elsevier]

Abstract: (Nd,Eu,Gd)Ba2Cu3O y (NEG) films were prepared on LaAlO3 single-crystal substrates by metal-organic deposition (MOD) using fluorine-free solutions of metal 2-ethylhexanates (2-EH) or metal naphthenates (MN) with a small amount of trifluoroacetic acids (TFA) added. The addition of TFA to fluorine-free solutions lowered the growth temperatures, promoted crystal growth, and improved the superconducting properties of NEG films. This was similar to the effects observed on the growth of superconducting films by TFA-MOD using metal-trifluoroacetates. We report the successful growth of NEG films with T c of 92.6K and J c of 0.36MA/cm2 without introduction of water vapor. [Copyright &y& Elsevier]

Abstract: To improve critical current density, J c, under magnetic fields and at 77K, some pinning centers have been introduced into REBa2Cu3O y films (RE: rare earth elements). Pinning centers have been distinguished as one-dimensional, two-dimensional or three-dimensional artificial pinning centers (APCs) on the basis of their structural dimension. One-dimensional and three-dimensional APCs have considerably improved J c as a result of our efforts. For example, BaZrO3 or BaSnO3 nanorods are significantly effective one-dimensional APCs. It is found that the nanorod structure can be controlled and the J c–B properties vary depending on the nanorod structure. Moreover, the principle of two-dimensional APCs, which have been successfully designed in a multilayer structure, has been clarified. In this paper, the microstructures of the one- and two-dimensional APCs, such as the nanorods and the boundaries, are described in particular. The J c–B properties also are discussed. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O7− x +BaSnO3 (YBCO+BSO) mixed films with increased BSO content were prepared on SrTiO3 substrates by pulsed-laser deposition of YBCO+ x wt% BSO mixed targets (x =2, 4, 6 and 8wt%). TEM images reveal that BSO is incorporated into the YBCO matrix in form of nanorods, whose density and size increase with the BSO content. The pinning properties for the mixed YBCO+BSO film were systematically studied. The 4wt% BSO sample exhibited the maximum global pinning forces FP at all temperatures: 28.3GN/m3 near 3T at 77K, 103GN/m3 near 5T at 65K, and >241GN/m3 near 9T at 40K. [Copyright &y& Elsevier]

Abstract: We investigated the influence of the BZO nanorods on the surface morphologies of conventional PLD-SmBCO film and the SmBCO film prepared by a low-temperature growth (LTG) technique, developed by us as a novel crystal growth method. Dynamic force microscope (DFM) images showed that growth modes in SmBCO including BZO nanorods films were transformed from spiral growth mode into the 2D nucleation and growth mode. Moreover, observations using the DFM showed growth steps of the PLD- and LTG-SmBCO. Plan-view transmission electron microscope (TEM) images suggested that the BZO pinned the growth of the SmBCO layer. [Copyright &y& Elsevier]

Abstract: To clarify the growth mechanism of YBa2Cu3O7− X (Y123) crystals in the multi-coated film fabricated by the trifluoroacetates–metal organic deposition (TFA–MOD) method, the growth processes of Y123 crystal grains were studied by the experimental method and the numerical method. Microstructures of growing Y123 crystals were revealed through transmission electron microscopy (TEM) observations of the specimens quenched during the growth of Y123 crystals on LaAlO3 (LAO) substrates. It was observed that some a-axis grains grow among many c-axis grains, and they have some terraces near the initial boundaries of multi-coated layers. The above terraces of a-axis grains were considered to form by the change in c-axis (c-plane) growth rate of a-axis grains, which may have some dislocations and/or stacking faults. The growth processes and the above microstructures of faceted Y123 crystal grains were also shown by the two-dimensional numerical simulation using c- and a-axes growth rate functions. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O y (YBCO) films grown by starting solutions with Ba-poor (Y:Ba:Cu=1:1.5:3, Ba/Y=1.5) have been reported to perform higher J c than that for YBCO films with stoichiometric one due to smaller and less pores in YBCO films by metal organic deposition (MOD) using tri-fluoroacetates (TFA). However, we have reported that a lot of non-reacted particles such as Y and Cu oxides were remained for the YBCO film surface grown by the precursors using Ba-poor solution. In this study, influences of YBCO growth rate on microstructures of the YBCO film were discussed to control microstructures of these second phase particles. As a result, microstructures of the YBCO film depended strongly on the YBCO growth rate, residues of Y and Cu oxides were dispersed randomly throughout the YBCO film grown at higher growth rate. Consequently, it was succeeded to control the segregated phases as seen in the previous YBCO film with Ba/Y=1.5 at the film surface into the YBCO film. J c of the YBCO film grown at higher rate was a value almost equal to that grown at previous growth rate. [Copyright &y& Elsevier]