Wakichi Kondo

Effects of Heat Treatment Conditions on the Critical Current Densities of Ba2YCu3O7-y Films Prepared by the Dipping-Pyrolysis Process

The effects of temperature and atmosphere on the BYCO formation reaction of BaCO3, Y2O3 and CuO, prepared by the pyrolysis of metal acetylacetonate solution, were examined by TG-DTA, XRD and resistivity measurement. This reaction was found to proceed readily below 900°C under low oxygen partial pressures. Superconducting Ba2YCu3O7-y films with Tc,zero\cong90 K and Jc(77 K)=300–400 A/cm2 were prepared by the dipping-pyrolysis process using the above solution through heat treatments at 820°–880°C under controlled low oxygen partial pressures of ρ(O2)=1×10-3–2×10-4 atm followed by O2 annealing.

Critical Current Densities at 77 K in Ba2YCu3O7-y-Ag Films Prepared by Dipping-Pyrolysis Process

Excellent critical current behavior at 77 K in magnetic fields up to 14 T has been obtained for Ba2YCu3O7-y(BYCO)-Ag films prepared by dipping-pyrolysis process. The films were epitaxially grown on SrTiO3(100) substrates using a two-step annealing (low-p(O2)/pure O2) method at 770°C. The best values of critical current density at 77 K under a 2-µV/cm criterion were 1.2×106 A/cm2 in a self field and 1.0×105 and 3.8×104 A/cm2 at 8 T and 14 T, respectively, when the field was applied parallel to the a-b plane.

Preparation of High-Jc Ba2YCu3O7-y Films on SrTiO3 (100) Substrates by the Dipping-Pyrolysis Process at 750°C

Superconducting Ba2YCu3O7-y films were prepared on SγTiO3 (100) substrates by the dipping-pyrolysis process using metal acetylacetonates as starting materials. Prefired films were heat-treated at 750°C under a low-oxygen partial pressure (p(O2)=2×10-4 atm) and then annealed in O2. The resulting films showed high superconducting transition temperatures; both of the values of Tc,onset(s) and Tc,zero(r) were 89 K. The current-voltage characteristics of the films were measured at 74-86 K. The critical current at 77 K and 0 T was 2.4 A, which corresponds to the critical-current density of 3.9×105 A/cm2.

Metal organic deposition of epitaxial Y123 films using a low-cost vacuum technique

Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) films were obtained by metal-organic deposition (MOD) using a simple, low-cost vacuum technique without gas flowing. The total pressure and oxygen partial pressure in the furnace were controlled to be 10 kPa and 10 Pa, respectively, by evacuation with a rotary pump followed by refilling with a mixture of O/sub 2/ and N/sub 2/ (O/sub 2/ content: 1000 ppm). XRD analyses exhibited that c-axis-oriented epitaxial Y123 films have successfully been obtained on CeO/sub 2/-buffered YSZ (100) (CbZ) and CeO/sub 2/-buffered sapphire (012) (CbS) substrates. In-plane alignments of these films were as high as that of the CeO/sub 2/ buffer layer. The film on the CbZ demonstrated a high critical current density J/sub c/ of /spl sim/2.1 MA/cm/sup 2/ at 77 K all over the film; the fluctuation of J/sub c/ being within /spl plusmn/10% of the average. Inductive T/sub c/ measurement showed a very sharp peak with T/sub c/=90.5 K. Inductive-J/sub c/ and T/sub c/ of the Y123 film on CbS were 1.1 MA/cm/sup 2/ and 89.6 K, respectively, whereas the T/sub c/ of the Y123 film on LaAlO/sub 3/ was lower than 77 K owing to the occurrence of the a-axis grains.

Effects of annealing conditions and substrate materials on the superconducting properties of Ba2YCu3O7-y films prepared by the dipping-pyrolysis process at 750°C

Superconducting Ba2YCu3O7-y (BYCO) films were prepared on various substrates by the dipping-pyrolysis process. The effects of annealing parameters, environment and time were also investigated. The 2-µm-thick films of BaCO3-Y2O3-CuO mixture were heat-treated at 750°C under a low-oxygen partial pressure (p(O2)=2×10-4 atm) followed by annealing under higher-p(O2) atmospheres. The resulting films showed high superconducting transition temperatures; values of Tc,onset(s)s were 89 K on SrTiO3(100), 86 K on LaAlO3(100), 86 K on yttria-stabilized zirconia (YSZ), 83 K on MgO(100), and 76 K on sapphire.

Preparation of Superconducting Ba2YCu3O7-y Films by the Dipping-Pyrolysis Process at 700° and 750°C

Superconducting Ba2YCu3O7-y (BYCO) films were prepared by the dipping-pyrolysis process using metal acetylacetonates as starting materials through heat treatments below 800°C under controlled low oxygen partial pressures (p(O2)s) followed by O2 annealing. Values of Tc,zero(r)s were greatly dependent on the temperature and p(O2) of heat treatment; they were 64 K and 85 K with the heat treatments at 700° and 750°C, respectively, under an initial p(O2) of 2×10-4 atm for 2-µm-thick BYCO films. Moreover, silver precoating was effective for improving the superconducting and surface properties of the films heat-treated at 700°C.

Preparation of Superconducting Ba2YCu3O7-y/Ag Composite Films by the Dipping-Pyrolysis Process Using Metal Naphthenates at 750°C

Superconducting Ba2YCu3O7-y/Ag composite films were prepared on yttria-stabilized zirconia substrates by the dipping-pyrolysis process. Metal naphthenates were used as starting materials. Homogeneous Ba-Y-Cu-Ag solutions with (Ag/BYCO) molar ratios of 0-1.0 were spin-coated onto the substrates and pyrolyzed at 500°C. Subsequently, these prefired films were heat-treated at 750°C under a low-oxygen partial pressure (=2×10-4 atm) followed by higher-p(O2) annealing. High superconducting transition temperatures, Tc,onset(s)s and Tc,zero

Preparation of Double-Sided YBCO Films on LaAlO 3 by MOD Using Commercially Available Coating Solution

(r)s, of 88 K-90 Kwereobtainedforthecompositefilmswith (Ag/BYCO) molarratiosof 0.1-0.5.

Preparation and Superconducting Properties of Bi-Pb-Sr-Ca-Cu-O Films (Tc=106 K) by the Dipping-Pyrolysis Process

The 5-cm-diameter double-sided YBa 2 Cu 3 O 7 (YBCO) films were prepared by metal organic deposition (MOD) using a commercially available metal-naphthenate coating solution. Firstly, YBCO film was prepared by MOD on one side of a double-side-polished 5-cm-diameter LaAlO 3 substrate. Secondly, another side was similarly coated with YBCO by MOD. After the latter processing, degradation of average J c value in the first side was not observed; but the fluctuation of critical current density J c slightly increased. The double-sided YBCO films showed average J c values of 0.8-1.0 MA/cm 2 at 77 K and microwave surface resistances R s (12 GHz) of 0.86-1.07 mΩ at 70 K.

Fabrication of Double-Sided YBa 2 Cu 3 O 7 Films on CeO 2 -Buffered Sapphire Substrates by MOD Process

Superconducting Bi-Pb-Sr-Ca-Cu-O (2223 as the major phase) films were prepared by the dipping-pyrolysis process on MgO(100) substrates using a metal naphthenate solution. From the XRD and SEM-EDX analyses, the formation of the 2223 phase with well-developed platelike grains was facilitated in the films by placing a Pb-containing BSCCO pellet on the surface of the prefired films during the heat treatment (850°C in air) and by the use of a nominal composition of Bi:Pb:Sr:Ca:Cu=1.8:0.4:2.0:2.4:3.6 in molar ratio, i.e., a Ca-and-Cu-rich composition compared to the 2223 phase. The values of Tc,zero and Jc(77 K) were 106 K and 2×103 A/cm2, respectively. The dependence of critical current densities on temperature showed that Jc was approximately proportional to (1-T/Tc)3/2, which corresponds to the results of the promixity junction tunneling (SNIS) model.