Y123 Layer Research Articles

Matching field effects in c-axis in-plane aligned a-axis-oriented YBa2Cu3Oy films with two-dimensional artificial pinning centers induced by multilayerednano-structures

A relationship between microstructures ofYBa2Cu3Oy (Y123)films with two-dimensional artificial pinning centers (2D APCs) and their critical current density (Jc), especially undermatching fields (Bϕ), is discussed. Using a pulsed laser deposition (PLD) method,c-axis in-planealigned a-axis-oriented Y123/Pr123 multilayer films were grown on substrates. ThePr123 interlayer distance was changed by controlling a target shape and itsrotation speed in the PLD process. The multilayer structure was observed incross-sectional transmission electron microscopy images. Critical temperaturesof the films decrease as the Y123 layer becomes thinner. The magnetic field (B) dependenceof Jc showed that the interlayers act as 2D APCs in multilayer films. The matchingeffects were observed in two ways: curves and irreversibility lines.

Superconducting transitions of Y-123/Ba-Ca-Cu-O/Y-123 layered structure

The highest critical temperature reported for the superconducting system Ba-Ca-Cu-O is Tc=117K. We have investigated the fabrication of systems consisting of Ba-Ca-Cu-O mid-layers sandwiched by YBa2Cu3O7-δ(Y-123) films. These trilayered structures were fabricated using pulsed laser deposition under 13.3Pa O2 pressure and on a SrTiO3 (100) substrate heated to 800–850°. The base Y-123 films were fabricated with the c-axis orientation and the roughness of all films was investigated using reflection high energy electron diffraction. We have not yet achieved a value of Tc above 100K. However, three successive onset superconducting transitions were observed in the magnetic susceptibility, for example at Tc-on = 76.8K, 81.0K and 85.7K for systems with a BaCa2Cu3Ox mid-layer. These three transitions, Tc1, Tc2 and Tc3, were assigned to the base and top Y-123 layers (thickness 100nm) and the BaCanCun+10z mid-layer (thickness 45nm), respectively. Moreover, the superconductive transition determined by resistivity measurements of Y-123/Ba2CanCun+10z/Y-123 trilayers was sharper (Tc=91.7–89.4) than that of Y-123 alone (Tc=92.2–88.2).

Growth process of Ba-poor YBCO film fabricated by TFA-MOD process

Metal organic deposition process using trifluoroacetates (TFA-MOD) is one of the most promising processes to fabricate YBCO film. It has been reported that YBCO films grown by the starting solution with Ba-poor (cation ratio as Y:Ba:Cu = 1:1.5:3) have higher J C value and has smaller and less pores than those of the YBCO film with stoichiometric composition. It is important to investigate the growth mechanism of YBCO crystals to obtain a high J C film by controlling the crystal structures. In this study, YBCO films were fabricated under various Ba concentrations in the TFA starting solution, and the influences of Ba composition on the growth process and microstructures were investigated. As a result, the Ba-poor YBCO film with Ba/Y = 1.5 and high J C had less a-axis oriented Y123 in comparison with the film with Ba/Y = 2. Furthermore, pores in the Ba-poor film were less than that in the stoichiometric composition film. This decrease of pores in the Ba-poor film was considered to be caused by the smaller size of non-reacted phases especially such as Ba–F rich particles entrapped by growing Y123 in the growing Y123 layer. It is considered that both the reductions of a-axis oriented Y123 and pores were the reasons of improving J C values in Ba-poor film.

Microstructure of Epitaxial Y123 Films on ${\rm CeO}_{2}$-Buffered YSZ Prepared by Fluorine-Free MOD

Epitaxial YBa2Cu3O7 (Y123) films have been prepared by fluorine-free metalorganic deposition (MOD) using a metal acetylacetonate-based coating solution on cerium oxide (CeO2: 40 nm)-buffered yttria-stabilized zirconia (CbYSZ) substrates. The 210-nm-thick Y123 film demonstrated a high critical current density (Jc), the average Jc being 4.5 MA/cm2 at 77.3 K using an inductive method. However, with increasing thickness the Jc values decreased; the average Jc was 3.4 and 2.2 MA/cm2 for 400-nm- and 550-nm-thick films, respectively. In low-magnification cross sectional transmission electron microscopy (XTEM) images for the films, the stripe-like contrast due to the c-axis orientation of Y123 was clearly seen from the interface with CeO2 to the surface. The whole c-axis-oriented Y123 layers were very dense even in the 550-nm-thick film. Full width at half maximum (FWHM) of Deltaomega for the 308/038 reflections in XRD omega - 2thetas scanning decreased with increasing film thickness. High resolution XTEM images of the 550-nm-thick film showed wavy c-planes of Y123 due to the short stacking faults near the interface with CeO2 buffer and near the surface whereas the c-planes were very flat but contained long stacking faults in the middle part of the film. It is suggested that the absence of wavy stacking faults, which probably work as pinning centers, decreased Jc in the thicker films. Further decrease in Jc in the 550-nm-thick film is presumably caused by the roughness in the outer layer near the surface.

Nanostructural characterization of Y123 and Gd123 with BaZrO3 rods fabricated by pulsed-laser deposition

Both YBa2Cu3O7−x (Y123) and GdBa2Cu3O7−x (Gd123) layers with BaZrO3 (BZO) rods were deposited on Hastelloy tapes with textured buffer layers (CeO2/Gd2Zr2O7) using pulsed-laser deposition (PLD). Two volume percent of YSZ–Y123 and 2vol%YSZ–Gd123 were used as target materials. The critical current density (Jc) values of these layers in a magnetic field parallel to the substrate normal were enhanced compared with those of Y123 layers without BZO rods. In the entire incident angle of magnetic fields, the Jc reduction of the Gd123 layer with BZO rods were improved compared to that of the Y123 layer with BZO rods. Transmission electron microscopy was used to characterize the nanostructures of the specimens prepared by both focused ion beam and standard ion milling. The Y123 layer with BZO rods and the Gd123 layer with BZO rods were composed of c-axis oriented grains, in which BZO rods aligned in the [001] of Y(Gd)123 ware distributed homogeneously. The diameter of the BZO rods was about 5nm and the rods grew from the CeO2 interface to the surface. The orientation relationships between Y(Gd)123 and BZO were as follows: (001)Y(Gd)123//(001)BZO and (100)Y(Gd)123//(100)BZO. In the Gd123 with BZO rods, a high density of stacking faults in the (001) plane and distorted (001) planes were found. The formation of the BZO rods in the Y(Gd)123 and a high density of defects with respect to the (001) plane in the Gd123 were considered to enhance the Jc values in high magnetic fields.

Growth and Structural Characterization of Needlelike Crystals in the Y−Ba−Cu−O System

A system formed by a bar of Y2BaCuO5 (Y211) phase supported on two YBa2Cu3Ox (Y123) pellets was processed by thermal treatment at high temperature. The first effect was a change in chemical composition inside the bar, yielding new phases: mostly Y123 and BaCuO2. Their concentrations were higher near the bar ends. A second, very interesting result was the growth of two kinds of acicular crystals underneath the whole bar: green, transparent Y211 needles and needles with a green core of Y211, covered by a Y123 layer. Micro Raman and SEM analyses clearly identified the two different phases. XRD inspection has confirmed that Y211 crystals are high-quality single crystals. The preferential growth direction for Y211 needles is along the crystallographic b axis. A possible explanation, based on the VLS mechanism, for their growth is suggested.

Microstructural observations of epitaxial Y123 films on CeO2-buffered sapphire by metal organic deposition

Epitaxial YBa2Cu3O7 (Y123) films were obtained on CeO2-buffered sapphire substrates by a fluorine-free MOD process. A 170-nm-thick homogeneous film revealed a high critical current density (Jc > 4 MA/cm2) at 77 K, whereas a 320-nm-thick film had a low Jc of 0.7 MA/cm2. Both of the films have neither a-axis orientation nor BaCeO3 phase by x-ray diffraction. In this article, the microstructures of these Y123 films were observed by crosssectional transmission electron microscopy. The epitaxial c-axis layers were observed successively from the interface with CeO2 buffer to the surface. Selected area diffraction (SAD) exhibited that the orientation relationship among the Y123, CeO2-buffer and sapphire substrate was: Y123(001)[110] ∥ CeO2(100)[100] ∥ Al2O3(-1012)[1-210]. The impurity phase on the surface was revealed to be a CuYO2 compound by energy dispersive X-ray spectroscopy and SAD. The Y123 grains on the surface of the 320-nm-thick film were somewhat inclined to the epitaxial Y123 layer; this is one of the reasons for degraded Jc in the thicker films.

Irreversible properties of YBCO thick films deposited by liquid phase epitaxy on single crystalline substrates

We report on the field and temperature dependence of the critical transport current density Jc, the angular dependence of the transport current at various external magnetic fields and the irreversibility fields in YBa2Cu3O7−δ (Y-123) thick films prepared by liquid phase epitaxy (LPE). A comparison of the irreversible properties between specimens produced with and without silver additions to the melt is also presented. Transmission electron microscopy (TEM) was employed to obtain information on the correlation between the transport properties and the microstructure. The samples were deposited either directly on NdGaO3 (NGO) or on seeded (100) MgO substrates, where a 200 nm thin YBCO film deposited by pulsed laser deposition (PLD) acts as seed layer for the LPE process. The final thickness of the Y-123 layer is of the order of 1 µm for the NGO and between 2 and 10 µm for the MgO samples. The critical current densities reach 3 × 109 A m−2 at zero field and 77 K in the best case.

Neutron irradiation studies on Y-123 thick films deposited by liquid phase epitaxy on single crystalline substrates

AbstractThe influence of neutron irradiation on the angular, field and temperature dependence of the critical transportcurrent density J c of YBa 2 Cu 3 O 7 d (Y-123) thick films, as well as on the irreversibility fields was investigated. Thespecimens were deposited by liquid phase epitaxy either directly on NdGaO 3 or on seeded (100)MgO substrates with afinal Y-123 layer thickness of 1 and 5–10 lm, respectively. XRD of the superconducting layers proves good in-planeand out-of-plane alignments with FWHMs below 2 . The specimens showed excellent irreversible properties withcritical current densities of up to 3 10 9 A/m 2 at zero field and 77 K and irreversibility fields above 7 T at 77 K for Hkcprior to neutron irradiation, which was performed in fast neutron fluence steps of 10 21 m 2 , corresponding to 5 10 21 defect cascades per m 3 per step. J c enhancements by 100% and an anisotropy reduction by a factor of 2 are achieved atthe optimum neutron fluence. 2003 Elsevier B.V. All rights reserved.

Fabrication of coated conductor using LPE process

We tried to apply the LPE process to fabricate RE123 coated conductors. We have been investigating the construction using a BaZrO 3 buffer layer, called “non-reactive buffer type” on the textured Ni substrate. It was confirmed that this construction is stable for the LPE process, because the BaZrO 3 is stable to the RE–Ba–Cu–O solution at the process temperature. First, Y123 was grown on the MgO single crystal substrate with the BaZrO 3 buffer layer in order to confirm the potential of this combination. We confirmed that the BaZrO 3 layer could be effective to prevent from chemical diffusion of Ni and a high superconducting performance cloud be obtained as T c=92 K and J c=2×10 5 A/cm 2. We prepared with the Sm123 seeded substrate on the BaZrO 3/SOE/textured Ni, and confirmed that the seed layer and buffer layer showed the fourfold symmetry in the crystal in-plane alignment. Y123 was tried to grow on this sample and it was confirmed that the BaZrO 3 buffer layer prevented from the reaction between the Ni substrate and the solution. Consequently, the Y123 layer with a good in-plane alignment was obtained and it showed high T c value of 90 K.

金属基板上へのRE123のLPE成膜

RE123 superconductive oxides are expected to be utilized for electric conductors due to its high superconducting performance at 77 K. The liquid phase epitaxy (LPE) process has an advantage to fabricate a thick superconducting layer at a high growth rate with high superconducting properties for realizing high Jc conductors. We tried two structures to fabricate in-plane aligned Y123 layer on textured Ni substrates with SOE-NiO. One was a double layered LPE structure and the other was a non-reactive buffered structure using a BaZrO3 buffer layer. The in-plane aligned Y123 LPE layer was successfully grown on an NiO/Ni textured substrate for each structure and the Tc value of 90 K was achieved in the non-reactive buffered structure. The in-plane alignment of the seed layer was found to be a crucial factor for the double LPE process since the partial dissolution of worse aligned seed crystals caused formation of non-coverage regions on the surface of the NiO buffer layer, where the NiO buffer layer would react with the solution during the second LPE processing.

TRANSPORT STUDIES ON NANOMETER THICK YBa2Cu3O7-δ MULTILAYERS USING Y0.4Pr0.6Cu3O7 AND PrBa2(Cu0.8Ga0.2)3O7 AS BUFFER LAYERS

We have fabricated PrBa2[Cu1-xGax]3O7 (PBGCO) ceramic samples for x = 0.05, 0.10, 0.15 and 0.20. The electrical resistivities of these samples are many orders of magnitude higher than that of PrBa2Cu3O7 (Pr123) while the other physical properties remain much the same. PBGCO therefore may be a possible buffer layer for YBa2Cu3O7-δ (Y123) superlattices/multilayers. For this reason YBa2Cu3O7-δ/PrBa2(Cu0.8Ga0.2)3O7 (Y123/PBCGO) and YBa2Cu3O7-δ/Y0.4Pr0.6Ba2Cu3O7 (Y123/YPBCO) superlattices were fabricated and their transport properties were studied. It is found that although PBGCO is better for insulating Y123 films in trilayers, inter-Y123 layer coupling exists between separated Y123 layer.

Growth of RE–Ba–Cu–O thick film on metal substrate by liquid phase epitaxy process

A liquid phase epitaxy (LPE) process on a metal substrate has been developed for the RE123 coated conductors. In order to prevent the reaction between the solvent and metal substrate, which is the first problem to be solved, for its development, an MgO buffer layer on the metal substrate was applied, since MgO is relatively stable in the liquid solvent. However, it disappeared when the substrate was dipped into the liquid. This phenomenon was clarified by a solubility measurement that was not due to melting but due to dissolution. Then, a combination of using a buffer layer and a saturated liquid by the MgO was considered to prevent the dissolution. Actually, the MgO buffer layer retained and it protects the Hastelloy substrate from the reaction. Additionally, it was clarified that there is little difference in Y 2O 3 solubility in the liquid with and without the MgO addition in the liquid. The Mg substituted Y123 LPE layer was grown at a similar growth rate even from MgO-saturated liquid under the same temperature conditions for the growth of Y123 from the solvent without MgO. Furthermore, the Y123 layer was grown from the liquid without MgO on the Mg substituted Y123 LPE layer to obtain the high superconducting characteristics. The double layered LPE film on MgO single crystal substrates revealed a high T c value of 90 K and a high J c value of 10 5 A/cm 2 at 77 K. Then, the new construction of RE123(LPE)/RE123–Mg(LPE)/MgO/Hastelloy was proposed for applying the LPE process to the coated conductor production. The fabrication of the construction on Hastelloy substrates was achieved.

LPE process application to RE123 coated conductor

The fabrication process of REBa 2Cu 3O y (RE123: RE=Y, Sm, Nd3·) system superconducting tapes was developed using the Hastelloy substrate by the liquid phase epitaxy (LPE) process. The reaction between Hastelloy and the BaCuO melt is prevented by an MgO buffer layer for the melt saturated with MgO. The suitable construction for tape processing by LPE was consequently found as YBa 2Cu 3O y (Y123) 〈by LPE〉 / YBa 2(Cu,Mg) 3O y (Y123(Mg)) 〈by LPE〉 / MgO / Hastelloy. The superconducting properties of the Y123 layer with this construction were confirmed on the MgO single crystal substrates. The Y123 / Y123(Mg) / MgO structure revealed a high T c value of 91 K and a J c value of 1.2×10 5 A/cm 2 (77K, 0T). For short smaples, the Y123(Mg) layer was successfully grown on Hastelloy substrate with MgO by the LPE process. For the fabrication of long LPE conductors, the ability of the long tape LPE apparatus was confirmed as a preliminary study in which the Y123 layer was grown on the MgO substrates by laterally moving the substrates on the melt surface.

Y-system coated conductor on metal substrate by LPE method

Utiligation of MgO as a buffer layer for LPE(Liquid Phase Epitaxy) growth of YBa 2Cu 3O y (Y123) was investigated. In order to investigate the reaction, the tapes with MgO layers were dipped into the melt of two different compositions. The tape was completely dissolved into the melt without addition of MgO. However, the tape survived in the MgO-saturated solution. The modified LPE process was developed which is the Y123 LPE growth using the Y123 layer saturated with MgO as the second buffer layer to prevent dissolution of the first MgO buffer layer into the melt.

MgO飽和溶液を用いた金属基板上YBCO-LPE膜の作製

The fabrication process of RE123 system superconducting tape on Hastelloy substrates was developed using the liquid phase epitaxy (LPE) process. To prevent reactions between metal substrates and the Ba3Cu5Ox solution, we selected an MgO buffer layer for the solution saturated with MgO. The Hastelloy substrate was completely dissolved into the melt without addition of MgO. However, the Hastelloy substrate survived in the MgO saturated solution. The modified LPE process was developed which is the Y123 LPE growth using the Y123 layer saturated with MgO as the second buffer layer to prevent dissolution of the first MgO buffer layer into the melt. Using the MgO single crystal substrates, we got the YBa2Cu3Ox film on the YBa2(Cu, Mg)3Ox/MgO substrates. Finally, the YBa2(Cu, Mg)3O layer was grown on MgO/Hastelloy substrates from the solution saturated with MgO.

Determination of the low critical magnetic fields in high temperature superconductor films

We present results of the determination of the lower critical magnetic fields: Josephson H c1J, H c2J and Abrikosov H c1J type for the Y-123 and Bi-2212 layers onto MgO substrate. Based on the DC magnetic field dependence of the real part χ′ of complex AC susceptibility we assumed that H c1J=3.1 Oe and H c2J=11.4 Oe for Y-layer and H c2J=4.5 Oe and H c1g=16.3 Oe for Bi-layer.