三浦 正志

In order to enhance the J(c) characteristics under the magnetic fields, we prepared Y1-xRExBa2Cu3Oy coated conductors (CCs) with artificial pinning centers by using the starting solution containing Zr-salt, where RE is Gd or Sm, in the trifluoroacetates-metal organic deposition. From microstructure observation, BaZro(3) (BZO) nanoparticles were uniformly dispersed in these films. High J(c) in the magnetic fields and significant enhancement of J(c) for all applied magnetic field angles were achieved. Especially, YGdBCO+BZO CCs showed the highest self-fields J(c) values (J(c)(sf)) of 4 MA/cm(2) and its minimum value of 0.64 MA/cm(2) at 77 K and 1 T. (C) 2009 The Japan Society of Applied Physics

Recent progress on the efforts for the high performances of I-c and I-c-B and the development of long tapes and extremely low cost tapes using the reel-to-reel system are reviewed. The control of the starting solution composition, especially for the Ba-poor composition from the Y:Ba:Cu = 1:23 stoichiometric one, is found to be effective to improve the J(c) value of the films. Consequently, the extremely high 1, Value of 735 A was obtained. On the fabrication of long tapes by the reel-to-reel system, it was found that the rigorous humidity control in the coating chamber is important to obtain the uniform characteristics in long tapes. The idea was applied to fabricate long tapes and a 56 m tape with the end-to-end I-c value of 250 A was realized. Additionally, a 1 m long tape using a textured NiW substrate was fabricated as an extremely low cost tape. The high end-to-end 1, value of 221 A was recognized in this tape. Concerning to the high production rate over 10 m/h which is one of the required conditions for the extremely low cost, new metal organic solution especially with F-free salt for Y was developed. and coating thicker than 0.5 mu m at 10 m/h for one coating and calcinations was achieved. Additionally, the possibility for the multi-turning system in the crystallization equipment was confirmed using the small furnace. (C) 2008 Published by Elsevier B.V.

For production of low cost coated conductor tapes, the TFA-MOD (metal organic deposition using trifluoroacetates) process is one of the promising methods and textured NiW alloy substrates are expected to be a candidate for their substrates. However, the superconducting properties obtained on the NiW substrates are not high enough due to lack of understandings on YBCO grain growth on the NiW. In this work. MOD growth conditions such as molar ratio (Ba/Y) of the starting solution, the crystallization temperature and P (O-2) (O-2 partial pressure) especially on the NiW substrates were studied. Compositional effects of the starting solution on I-c values have a trend having the highest value at Ba/Y = 1.5, which is similar to those on IBAD substrates, though the I-c values of YBCO on NiW are lower. One of the differences between YBCO layers on NiW and IBAD could be explained by the significant difference in a-axis oriented grain growth. The higher temperature and/or the lower PO2 were required to suppress the nucleation for a-axis oriented grain growth on the NiW. 1 m-long RTR production exhibited end-to-end I-c value of 221 A/cm w. which could be improved further by the optimization of the pro the cess conditions. (c) 2008 Elsevier B.V. All rights reserved.

The CeO2 buffer layer was fabricated using the multi-plume pulsed laser deposition (PLD) method with different deposition rates controlled by the excimer laser energy and frequency on the Gd2Zr2O7 template tape formed by the ion-beam assisted deposition (IBAD) with 14 degrees of A(P (full width at half maximum (FWHM) value of X-ray diffraction phi-scan for Gd2Zr2O7 (222) pole). The laser conditions with high pulse energy and low frequency resulted in a highly textured in-plane grain alignment (Delta phi). The surface roughness and Delta phi values were improved by increasing the thickness of the CeO2 buffer layer. YBCO films with the thickness of 1 mu m and 1.6 mu m were further deposited by the advanced trifluoroacetates-metal organic deposition (TFA-MOD) on the CeO2 buffered substrates with the deposition rate of 0.15 and 05 mu m/min. The J(c) values of 2.5 MA/cm(2) and 2 MA/cm(2) were obtained, respectively. High J(c) films could be deposited on the CeO2 buffer layer even at high deposition rate by the multi-plume deposition. (C) 2008 Elsevier B.V. All rights reserved.

We prepared REBa2Cu3Oy (REBCO) coated conductors (CCs) with high I-c values from the Ba-poor (Ba/Y < 2) solution compared with conventional CCs with the Y:Ba:Cu = 1:2:3 stoichiometric composition, In this study, we fabricated Y1-xSmxBa1.5Cu3Oy (YSmBCO) CCs under different experimental conditions of the maximum heating temperature and the oxygen partial pressure, in order to investigate the influence of fabrication conditions on microstructures and superconducting properties of the films for high I-c under magnetic fields. The YSmBCO film fabricated from the optimized condition showed high I-c especially at the high magnetic fields compared with the Sm-free YBCO films. The magnitude of the pinning force (F-p) of the optimized YSmBCO film increased under the high magnetic fields and the maximum F-p (F-p.max) value shifted to higher fields compared with those of Sm-free YBCO films. These results suggest that pinning centers were successfully introduced by the optimized fabrication conditions and the chemical substitution of Sm into the Y site enhanced F-p under the high magnetic fields in the YSmBCO coated conductors. (C) 2008 Elsevier B.V. All rights reserved.

We introduced artificial pinning centers for trifluoroacetates (TFA)-metal organic deposition (MOD) Y1-xSmxBa1.5Cu3Oy coated conductors to enhance critical current density (J(c)) under magnetic fields and to improve the magnetic field angular dependence of J(c)(J(c)-B-theta). The coated conductors showed high J(c) values and isotropic J(c)-B-theta property with the ratio J(c,min)/J(c,max) of 0.91 (77K, B = 1 T). From a microstructural observation, BaZrO3 (and/or ZrO2) nanoparticles were uniformity dispersed in the films. The uniform dispersion of nanoparticles was maintained not only along the lateral direction but also in the thickness one. It could be considered that the nanoparticles in the TFA-MOD REBCO coated conductors may act as pinning centers to enhance the J(c) in all field orientations. (c) 2008 The Japan Society of Applied Physics.

The introduction of the c-axis-correlated disorder is a promising technique for the improvement of the critical current density J(c) for B // c of REBa(2)Cu(3)O(y) (RE123) films and tapes. In order to understand the vortex pinning mechanism with the different variety of the c-axis-correlated disorder, the angular dependence of J(c) was measured in detail for an Y123 film with BaZrO(3) nano-rods, a Sm123 film with fine nano-particles and edge dislocations and an Y123 film with columnar defects introduced by the heavy-ion irradiation parallel to the c-axis. We found that the vortex pinning state for the variety of the c-axis-correlated pinning is similar in low fields below the matching field, but it shows different behaviors in high fields above the matching field. It is considered that the interstitial vortices interacted with the c-axis-correlated disorders through the vortex interaction may play an important role for the appearance of the c-axis-correlated pinning behavior in a high-field region above the matching field. (C) 2008 The Japan Society of Applied Physics.

The critical current density J(c) and resistivity rho of REBa2Cu3Ox (RE123) films were evaluated in high magnetic field and wide temperature regions. We use three different samples such as a heavy ion irradiated Y123 film, a BaZrO3 (BZO) added Y123 film and a low temperature growth Sm1-xBa2+xCu3Oy (LTG-Sm123) film. In these films, there exist the different c-axis correlated disorders like columnar shaped fission tracks for the heavy ion irradiated Y123 film, columnar shaped BZO precipitates for the BZO added Y123 film and edge dislocations at grain boundaries for the LTG-Sm123 films. The large peak of the angular dependence of J(c) for B//c direction was observed for all samples measured in this study in a low field region, suggesting that the c-axis correlated pinning works well for these samples. However, we found that the behavior of the J(c) peak for B//c strongly depends on a sort of c-axis correlated pinning centers. In the case of the columnar shaped fission tracks in the Y123 film, the J(c) peak for B//c increases monotonically with increasing a magnetic field and seems to be connected with the dip structure in the angular dependence of rho. In the case of the columnar shaped BZO precipitates, however, the J(c) peak for B//c vanishes in a high field region above a few tesla and no dip behavior of rho was observed. On the contrary, in the case of the edge dislocations for LTG-Sm123 film, the J(c) peak for B//c shrinks with increasing field and almost vanishes. But it grows again with further increasing a magnetic field and the dip of the angular dependence of rho is also observed. Hence the vortex pinning phase diagram strongly depends on a sort of c-axis correlated pinning centers. It is considered that these different behaviors of the J(c) peak for B//c are related to the competition of the random and c-axis correlated pinnings.

A critical current density J(c) and an irreversibility field B-i were measured for the low temperature growth (LTG) processed Sm1+xBa2-xCu3Oy, films with and without Sm-rich123 nano-particles. The reduction of the resistivity and the small enhancement of B-i due to the c-axis correlated pinning were observed for both LTG-Sm123 films with and without nano-particles. These results suggest that the c-axis correlated pinning affects similarly the resistivity and the B-i properties regardless of the nano-particle addition. In the J(c) properties of the nano-particles added sample, three peaks in the angular dependence of J(c) at 77.3 K appear in addition to the intrinsic anisotropy described by the effective mass model. Those are a broad peak for B parallel to c, a sharp peak at B parallel to ab and a shoulder at about 20 degrees off ab-plane. The broad peak at B parallel to c, which is related with the c-axis correlated pinning, decreases in low fields up to 3 T but increases again in a high field region with increasing a magnetic field. These behaviors may be connected to the enhancement of the B-i, which was obtained by the resistivity measurements. The global pinning force is scaled well in a low field region, but shifts to the low field direction in a high field region, with decreasing temperature. (C) 2007 Elsevier B.V. All rights reserved.

In order to achieve further lower substrate temperature (T,) of YBa2Cu3Oy (YBCO) thin films for coated conductor application, we developed low temperature growth (LTG) It technique. In the LTG II technique, a c-axis oriented (Yb1-xNdx)Ba2Cu3Oy thin layer was deposited on MgO substrate as seed layer at low T-s and then YBCO layer was fabricated on the seed layer at the same T-s. As a result, we achieved that the LTG II-YBCO thin films showed complete c-axis orientation at lower T-s than that for obtaining C-axis oriented PLD-YBCO thin films by 15 degrees C, and showed a high J(c). We discussed the orientation mechanism of the LTG II-YBCO thin film using a simple nucleation model. (C) 2007 Elsevier B.V. All rights reserved.

We have fabricated Sm1+xBa2-xCu3Oy (SmBCO) multilayer (Multi-SmBCO) films with alternating main SmBCO (x = 0.04) layers and additional Sm-rich (x = 0.08) layers. We confirmed that Cu2O precipitates in PLD-SmBCO films increased with increasing film thickness, though those in the Multi-SmBCO films hardly appeared even in thick films. I-c of the Multi-SmBCO film with a 1.7 mu m thickness achieved 800 A/cm-width (J(c) = 4.6 MA/cm(2)) at 77 K. Furthermore, the Multi-SmBCO film showed improved J(c) at all magnetic field, especially, at high-magnetic fields. The enhancement of J(c) in the high-magnetic fields would be related to Sm-rich phase (low-T-c phase) formed by introducing the Sm-rich layers. (C) 2007 Published by Elsevier B.V.

We have studied SmBa2Cu3Oy (Sm123) thin films fabricated by low temperature growth (LTG) technique. The critical current den. particles (NLP) were comparable to that of sities (J(c)s) in magnetic fields at 77 K of the LTG-Sm123 film embedded nanosized low-T. NbTi wire at 4.2 K. Furthermore, at low temperatures of 65 and 40 K, the J(c)-B curves of the LTG-Sm123 film were superior to even that of Nb3Sn wire at 4.2 K and the anomalous peaks were observed on the J(c)-B and F-p-B curves. Based on the scaling of the flux pinning force, we found that fluxes in the film would be pinned at grain boundary mainly and the anomalous peaks were caused by the NLP. (C) 2007 Elsevier B.V. All rights reserved.

We have studied the artificial pinning center (APC) techniques in Sm1+xBa2-xCu3Oy (SmBCO) films deposited on single crystalline substrates. As a result, using the low temperature growth (LTG)-PLD technique, J(c) of 0.28 MA/cm(2) at 77K, B=5T (B parallel to c) was obtained on 700 run thick SmBCO films grown on 50 nm thick SmBCO-seed buffered MgO substrate. Following the successful demonstration of the growth of SmBCO films on single crystalline substrate, the LTG technique was also extended to coated conductor on metal substrates. With the objectives of applying the superconducting magnetic application that operate at liquid nitrogen temperature, we report the Jc in magnetic field and the microstructure of SmBCO coated conductor. PLD-SmBCO with a J(c), of over 0.1 MA/cm(2) at 5 T (B parallel to c, 77 K) were grown on IBAD-YSZ/CeO2 tape, which is higher than YBCO/IBAD. In addition, the J(c), values of the SmBCO coated conductor grown with LTG technique measuring 0.23 MA/m(2) for 5 T of B parallel to c at 77 K are comparable to that of NbTi for 5 T at 4.2 K. From the magnetic field angular dependences of J(c) the anisotropy of the SmBCO film/IBAD tape is small. This performance in SmBCO coated conductor on metal substrate is comparable to the best results of SmBCO films on MgO single crystalline substrates. We discussed about the elemental mapping of the high-J(c) SmBCO coated conductor measured by TEM-EDX. (C) 2007 Elsevier B.V. All rights reserved.

REBa2Cu3Oy films require a high critical current (I,) under a high magnetic field at 77 K when using power applications. In this study, we fabricated Sm1.04Ba1.96Cu3Oy (SmBCO) thick films prepared using a low-temperature growth (LTG) technique in order to improve crystal quality and enhance flux pinning. The LTG multilayer thick film using a (SmBCO/Sm-rich layer) x N (N = 1, 2,...) multilayer system showed a high crystal quality. Additionally, the LTG multilayer thick film showed not only a high density of dislocations but also low-T-c particles within a high-T-c matrix. Therefore, the LTG multilayer film showed an I-c of 20.6 A/cm-width (77 K, B // c, B = 5 T) and had a thickness of only 1.35 mu m and a low anisotropy I-c for the high-magnetic-field direction. These results support to the developing possibility of power devices using a solenoid-type coil.

A high critical current density J(c) at 77.3 K and a high irreversibility field for B parallel to c were achieved for low-temperature-growth processed SmBa2Cu3O7 (LTG-Sm123) films. Transport properties of the LTG-Sm123 films with high J(c) were measured in high magnetic fields up to 17 T. We found a small enhancement of the irreversibility field due to the c-axis correlated pinning. We also observed the large peak for B parallel to c in a low field region below 1 T and 77.3 K. Those behaviors are originated with the c-axis correlated pinning. The peak at B parallel to c decreases in a low field region but increases again above 3 T with increasing a magnetic field. These J(c) behaviors are considerably related with the enhancement of irreversibility field. From experimental results obtained in this study, we proposed new pinned glass states near the irreversibility field.

Coated conductors for power applications require REBCO films with high critical currents (I-c). However, REBCO thick films were likely to be a-axis oriented so that I-c was saturated with increasing the film thickness. Previously we reported that Sm-rich (Sm1+xBa2-xCU3Oy; x = 0.08) films grown at low deposition temperatures on MgO substrates showed the complete c-axis orientation and the large terrace width as compared with SmBCO (Sm1+xBa2-xCU3Oy; x = 0.04) films. In this study, we will propose a novel multilayer technique in order to suppress the a-axis growth and keep large terrace width. In this technique thin Sm-rich layers are inserted among SmBCO layers. The multilayer structures [Sm - rich/SmBCO] * N (N = 1, 2, 3, ...) was fabricated by PLD method on MgO substrates. Although 1, in the SmBCO single layer films at 77 K was saturated at about 350 A/cm-width over the thickness of about 1.3 mu m, the SmBCO multilayer films with a thickness of 1.7 mu m showed the complete c-axis orientation, and the I-c achieved about 800 A/cm-width at 77 K. We confirmed that the growth of the a-axis oriented regions was suppressed by the Sm-rich layers. It is considered that the Sm-rich layers act as a template layer for maintaining the c-axis orientation, even though the surface temperature decreased with the thickness.

We have reported high-J(c) Sm1+xBa2-xCU3Oy (SmBCO) films on single crystal MgO prepared by pulsed laser deposition (PLD). In this study, we fabricate SmBCO films on metallic substrates using low temperature growth (LTG) technique, to investigate the availability of the LTG technique for coated conductors. The LTG-SmBCO films are deposited on PLD - CeO2/IBAD - YSZ/Hastelloy tapes. The critical current density (J(c)) is 4.7 MA/cm(2) (77 K, B//c, B = 0 T) and 0.23 MA/cm(2) (77 K, B//c, B = 5 T). Furthermore, at 65 K and B = 17 T, the J(c) of LTG-SmBCO film (B//c) reaches 0.03 MA/cm(2). These values are higher than those of conventional PLD-YBCO and PLD-SmBCO films. From these results, we suggest that the LTG is an effective technique for improving the magnetic field dependence of J(c) of coated conductors.

The authors found that the peak at the parallel external field (B parallel to c) to the c axis in the angular dependence of J(c) shrinks and almost disappears with increasing a magnetic field but it grows again with further increasing of a magnetic field at various temperatures for high-J(c) Sm1+xBa2-xCu3Oy films. These behaviors can be explained by the flux pinning properties of the interstitial vortices, which locate in between the vortices pinned by the c-axis correlated disorders. From the obtained experimental results, the collective correlated pinned glass state is proposed in a high field region in the vortex glass states. (c) 2007 American Institute of Physics.

We have reported high-J_c Sm_1+xBa_2-xCu₃O_y (SmBCO) films prepared by a low-temperature growth (LTG) technique. Despite the low-substrate temperature, the LTG-SmBCO films showed complete c-axis orientation and cube-on-cube texture. In addition, the LTG-SmBCO films showed a J_c of 0.28 MA/cm² (77 K, B//c, B=5 T), because these included high-dislocation densities and nanosize low-T_c particles. In this study, we discuss the mechanism of c-axis orientation and crystal growth for high-J_c LTG-SmBCO films. We newly suggest a model for "Nucleated growth on c-axis oriented Seed layer (NCS)" to understand the c-axis orientation mechanism for LTG-SmBCO films. Based on the NCS model, when the LTG-SmBCO films nucleated on a seed layer have two-dimensional (2D) nuclei with a 1 unit SmBCO step cell height, the interfacial energy between the nucleus and the seed layer and the critical Gibbs free energy of the nucleus are lower than those of PLD-SmBCO films. Therefore, the LTG-SmBCO films show high crystal quality and a wide processing window for biaxial orientation. We suggest that the LTG technique is effective for not only increasing J_c in magnetic fields, but also improving the processing window and crystal quality.

Practical utilization of a coated conductor as a superconducting magnet operating at 77 K requires not only an improvement in the J(c) at self field but also suppression of any decline in the Jc value in the magnetic field. In this study, nanoparticles and crystalline defects were created as the flux pinning in a high-J(c) Sm1+xBa2-xCu3Oy film during a film deposition process. We obtained extremely high-Jc values, J(c) = 0.37 MA/cm(2) (77 K, B parallel to c, B = 5 T) and J(c) = 0.1 MA/cm(2) (77 K, B parallel to c, B = 8 T). Cross-sectional low magnification and high-resolution TEM micrographs confirm the presence of Sm-enriched nanoparticles (x value > 0.2) embedded in the SmBCO lattice; typical particle sizes were 15 nm and particle density about 10(10)-10(11) particles cm(-2). We discussed about the elemental mapping of the high-J(c) SmBCO films measured by TEM-EDX. (c) 2006 Elsevier B.V. All rights reserved.

We have reported SmBa2Cu3Oy (Sm123) films prepared using a pulsed laser deposition (PLD) method. In particularly, Sm123 thin films prepared using a low temperature growth technique (LTG) could achieve a high-J(c) in a magnetic field at 77 K comparable to that in a Nb-Ti wire at 4.2 K. In order to clarify a mechanism of high-J(c) in LTG-Sm123 films, we compared an X-ray reciprocal space mapping (RSM) and a carrier concentration in the LTG films with those in PLD films. Although a Sm123 peak split on the RSM which corresponds to an orthorhombic structure, was observed in the PLD films with a thickness of >= 100 nm, the LTG films did not show such split. Further, from an annealing time dependence of the carrier concentration, a carrier injection into the LTG films tended to be difficult as compared to that into the PLD films. These facts imply that the LTG technique gives a high crystallinity. Therefore, we concluded that one of reasons of the high-J(c) in the LTG films was an improvement of crystalline uniformity such as an orientation and a lattice constant. (c) 2006 Elsevier B.V. All rights reserved.

We have fabricated epitaxial films of high-J(c) SmBCO using a low-temperature growth technique (LTG). The angular dependence of J(c) and composition analysis showed that the LTG-SmBCO films included nanosize low-T-c phases within the high-T-c matrix, the LTG-SmBCO films showed J(c) = 0.28 MA/cm(2) (77 K, B parallel to c, B = 5 T). However, number density of low-T-c phase is still less than the amount which is desired for complete flux-pinning at high-magnetic field. We deposited LTG-SmBCO including 1.4-2.8 vol.% of low-T-c nanoparticles. The films with 1.4 vol.% nanoparticles showed J(c) = 0.37 MA/cm(2) (77 K, B parallel to c, B = 5 T) and 0.10 MA/cm(2) (77 K, B parallel to c, B = 8 T). We speculated that the behaviors of the J(c)-B at high-magnetic field depend not only on distribution and size of low-T-c regions, but also the Sm/Ba composition within the low-T-c regions. (c) 2006 Elsevier B.V. All rights reserved.

Dislocations are effective flux-pinning centers in REBa2Cu3Oy films at a magnetic field. To investigate the relationship between critical current density (J(c)) and dislocation density, we discussed the dislocations in conventional pulsed-laser-deposition (PLD)-SmBCO films, vapor-liquid-solid (VLS)-SmBCO films, and low-temperature growth (LTG)-SmBCO films. The LTG-SmBCO and VLS-SmBCO films showed high-J(c) at low magnetic fields. From the observation of etch pits, we found that the LTG-SmBCO and VLS-SmBCO films had high-dislocation densities. We speculate that J(c) at low-magnetic fields is affected by dislocation density. LTG is effective for increasing dislocation density without deteriorating crystallinity or superconducting properties.

Sm1+xBa2-xCu3Oy (SmBCO) films prepared by the low-temperature growth (LTG) technique showed a critical current density (J(c)) as high as 0.28 MA/cm(2) (77 K B // c, B = 5 T). However, J(c) was lower than that of NbTi wire (4.2 K) above 5 T. In this study, we introduced nanoparticle superconductors with a low critical temperature (low-T-c) into LTG-SmBCO "LTG-SmBCO + nanoparticle" films to improve J(c) under the high magnetic field, and obtained an extremely high J(c), 0.1 MA/cm(2) (77 K B // c, B = 8 T). Energy-dispersive X-ray spectroscopy (EDX) showed that the "LTG-SmBCO + nanoparticle" films had a nanosize low-T-c phase and a low-T-c network dispersed in the high-T-c matrix. We concluded that the "LTG-SmBCO + nanoparticle" films could have enhanced J(c) by the introduction of pinning centers and the improvement of irreversibility field (B-irr).

We have reported high-J_c Sm_1+xBa_2-xCu₃O_y (SmBCO) films prepared by a low-temperature growth (LTG) technique. The LTG-SmBCO films showed a J_c of 0.28 MA/cm² (77 K, B//c, B=5 T). However, the J_c of these films in the magnetic fields above 5 T dropped and were lower than that of NbTi wire (4.2 K). In this study, we introduced nanoparticles with low T_c (low-T_c-nanoparticles) into LTG-SmBCO films to improve the J_c at the high magnetic field. The LTG-SmBCO + 1.4 vol.% nanoparticle film result in a J_c of 0.37 MA/cm² (77 K, B//c, B = 5 T) and 0.10 MA/cm² (77 K, B//c, B = 8 T). Furthermore, the J_c at 65 K in a field of 16 T (B//c) reached 0.05 MA/cm². Elemental mapping clarified that LTG-SmBCO + 1.4 vol.% nanoparticle film had nanosized low-T_c particles with an x of 0.15-0.30 and low-T_c network with an x of 0.05-0.15, which were dispersed in the high-T_c matrix. We speculate that the J_c under high magnetic field conditions depends not only on the distribution and size of low-T_c regions, but also on the Sm/Ba composition within the low-T_c regions.

Microstructure deformation has been investigated for EuBa2Cu3Ox films associated with orthorhombic-tetragonal transition during cooling in an oxygen atmosphere. EuBa2CU3Ox films have been grown by a pulsed laser deposition technique under 1000 mTorr oxygen pressure and 800 degrees C substrate temperature. After the growth, the films are cooled to 400 degrees C and annealed in one atom oxygen pressure for 0-110 h. The preferred orientation of the films is characterized by X-ray diffraction and phi-scan X-ray diffraction. Microstructures and lattice images of the EuBa2Cu3Ox films are observed by a transmission electron microscope. All of the obtained EuBa2Cu3Ox films are c-axis oriented. The phi-scan X-ray diffraction revealed that films without any 500 degrees C annealing have a tetragonal structure. However, more than 3 h annealed films are partly orthorhombic from the peak separation in the phi-scan. The angle between the two peaks is about 0.8 degrees. We estimate the a-axis length/b-axis length ratio (orthorhombicity) from the angle between the separated peaks to be 0.866 degrees. It agrees with the a-axis length/b-axis length ratio of well oxidized EuBa2Cu3Ox bulk materials. (c) 2005 Elsevier B.V. All rights reserved.

We have investigated the superconducting properties and the microstructure of c-axis oriented Sm1+xBa2-xCu3O6+y (SmBCO) thin films deposited on MgO substrates by pulsed laser deposition (PLD). In particularly, the use of thin c-axis oriented seed layer grown at high temperature enabled us to obtain fully c-axis oriented SmBCO films at relatively low temperature (similar to 740 degrees C). The values of T-c for the present films are within the range of 91.5-92.5 K. From their J(c)-B characteristics, it has been observed that the superconducting properties of SmBCO (x = 0.04, 0.08) films are superior to those of the YBa2Cu3O7-y thin films for B parallel to c, 5 T at 77 K. The J(c) values of the SmBCO films measuring 2.8 x 10(5) A/ m(2) for 5 T of B parallel to c at 77 K are comparable to that of NbTi for 5 T at 4.2 K. Furthermore, the superconducting properties in SmBCO change with the substitution of Sm-Ba. The Electron microscopic studies with EDX and S-TEM analysis have revealed that the Sm/Ba ratio fluctuates within the range of x = 0-0.14 with a wavelength of similar to 100 nm. High-J(c) values in high magnetic fields at 77 K demonstrate the potential of REBCO films for high-field applications of oxide superconductor. (c) 2005 Elsevier B.V. All rights reserved.

We have fabricated films of high-J(c) Sm1+xBa2-xCu3O6+delta (SmBCO) using a low temperature growth (LTG) technique. The self-field J(c) of LTG-SmBCO film increased with decreasing the substrate temperature at the upper layer fabrication (T-s,T-upper). From X-ray phi-scan measurement, we confirmed three kinds of in-plane rotated grains in the LTG-SmBCO films. The main peaks correspond to the grain with a [100](MgO)broken vertical bar broken vertical bar[100](SmBCO). Other small peaks observed from the grain with 45 degrees rotation and 45 +/- 8 degrees rotation decreased with decreasing T-s,T-upper. We considered that high-J(c) SmBCO films resulted from the improvement of the in-plane alignment. (c) 2005 Elsevier B.V. All rights reserved.

Rutile structure TiO2 buffer layers and YBa2Cu3O7-x (YBCO) thin films have been deposited on (100) MgO substrates by RF magnetron sputtering. It was found that, high quality c-axis oriented YBCO thin films could be obtained on MgO with very thin (110) oriented rutile structure TiO2 buffer layers. The crystal structure of TiO2 thin films changed from (100) oriented anatase structure TiO2 to (110) oriented rutile structure TiO2 with increasing substrate temperature. The (110) oriented rutile structure TiO2 thin films deposited with the optimal deposition condition had smooth surfaces. YBCO thin films on (110) oriented rutile structure TiO2 buffer layers had better crystallinity and surface flatness than YBCO thin films deposited on bare MgO substrates.

A c-axis oriented epitaxial REBa2Cu3Oy (RE123) thin film performs excellent superconducting properties in magnetic field. Recently, we reported that a critical current density (J(c)) in the RE123 thin film was improved by a deliberate composition control. A Sm1+xBa2-xCu3Oy (Sm123) thin film with a small amount of Sm/Ba substitution x showed the great J(c) similar to 0.17 MA/cm(2) in 5 T at 77.3 K, while the J(c) in (Yb1-zNdz)Ba2Cu3Oy (Yb/Nd123) thin films depended on an amount of mixed crystal ratio z. In this report, we studied J(c) as a function of magnetic field and field orientation with respect to ab-planes. In low magnetic field, the J(c) of Sm123 thin film was almost independent of the applied angle of the field. In the case of Yb/Nd123 thin film, extremely high J(c) were observed when the magnetic field was aligned parallel or perpendicular to the surface of the film. Because compositional fluctuations in RE123 thin films were observed by transmission electron microscopy, we found that the pinning centers in RE123 thin films are strongly affected by the composition in the thin films.

We have reported superconducting properties of Sm1+xBa2-xCu3Oy (SmBCO; x = 0.08) thin films prepared by the low temperature growth technique (LTG). LTG process is consisted of two steps as follows; a seed layer is deposited at 830 degrees C on MgO(100), and then upper layer is deposited at 740-780 degrees C on the seed layer. In order to investigate the effect of the fluctuations Sm/Ba composition ratio in the SmBCO matrix, we deposited upper layer with the Sm/Ba composition of x = 0 - 0.12. The SmBCO films with x = 0.04 and 0.08 show critical current density (J(c)) at 77 K of up to 5 x 10(6) A/cm(2) under 0 T and 1 x 10(5) A/cm(2) under 5 T for B//c at 77 K, respectively. The J(c) of x = 0.12 film dropped more sharply compared with the cases of x = 0.04 and 0.08 films. From the microstructure analysis, it was found that the main phase of x = 0.12 film was Sm-rich (Sm1.1Ba1.9Cu3Oy) phase, while that of x = 0.04 and 0.08 films was stoichiometry. We speculated that the low-J(c) of x = 0.12 film in the magnetic fields was ascribed to the low physical meters of T-c and irreversibility field of the Sm-rich SmBCO main phase.

In oxide-based superconducting thin films, conceivable factors that give rise to a pinning center include dislocations, precipitates, twin boundaries, and a-axis-oriented phases. In this study, crystalline defects were created perpendicular to a high-J(c) Sm1+xBa2-xCu3Oy film surface during a film deposition process. We obtained extremely high J(c) values, J(c) = 0.37 MA/cm(2) (77K, B // c, B = 5T) and J(c) = 0. 1 MA/cm(2) (77K, B // c, B = 8T). These values are equal to or exceed that of the previously reported NbTi wire material measured in a high magnetic field at 4.2 K.

High quality hetero-epitaxial CeO2 films are grown on MgO3 substrates using BaSnO3 buffer layers. CeO2 films and BaSnO3 buffer layers are grown by a pulsed laser deposition method. It is found that the crystallinity of the CeO2 films directly grown on MgO substrates is quite poor. However when we grow CeO2 films on MgO substrates with a BaSno(3) buffer layer, the crystallinity of CeO2 films is improved from that of the directly grown CeO2 films. Also the estimated in-plane crystallinity (80) of the CeO2 films on the BaSnO3 buffer layers is much improved by the introduction of the buffer layers. One of the reasons for high quality CeO2 films are grown on MgO substrates by the introduction. of BaSnO3 buffer layers is the lattice matching between the CeO2 films and the MgO substrates. The CeO2 films grow in a 45 rotated mode to the BaSnO3 buffered MgO substrates, then the lattice mismatch between the sublattice of the CeO2 films and the MgO substrates is calculated to be 9.3%, while that of the CeO2 films on MgO substrates in a cube on cube mode is over 25%.

We developed a low-temperature growth (LTG) technique as a novel deposition process to obtain RE_1+xBa_2-xCu₃O_y (REBCO) thin films with high superconducting properties. SmBCO films fabricated using the LTG-technique (LTG-SmBCO) showed complete c-axis orientations at a low substrate temperature (T_s). This T_s is about 100°C lower than the T_s when fabricating c-axis oriented SmBCO films using the conventional vapor growth method. Moreover, the critical current density (J_c) of the LTG-SmBCO in magnetic fields at 77 K has been improved reaching a high value of 0.17 MA/cm² at 5 T (B//c). The magnetic field angular dependence of the J_c at 77 K in LTG-SmBCO had a smaller anisotropy than that in PLD-SmBCO. From the microstructure observation, we found that the LTG-SmBCO showed a compositional fluctuation in Sm/Ba. We assume that the high J_c of LTG-SmBCO was affected by the solid solution acting as three-dimensional pinning center. From the viewpoint of diffusion in the solid phase, we speculated that this solid solution was generated by the low T_s.