I. Hirabayashi

High oxygen pressure synthesis of the PrBa2Cu4O8 compound

Abstract The PrBa 2 Cu 4 O 8 compound with a trace of BaCuO 3 and PrBaO 3 was synthesized for the first time by annealing at the temperature or 957°C under 5 atm oxygen pressure. The content of the PrBaO 3 is estimated to be less than 0.2%. The superconducting transition was not detected down to 2 K. The magnitude of the resistivity and its temperature dependence are consistent with the possession of a metallic character in this compound in contrast to the semiconducting behavior reported previously for the PrBa 2 Cu 3 O 7- δ compound. The effective magnetic moment, μ eff , estimated from the Curie-Weiss fitting to the magnetic susceptibility data, turns out to be 2.67 μ B .

Firing condition for entire reactions of fluorides with water vapor in metalorganic deposition method using trifluoroacetate

To obtain the YBa 2 Cu 3 O 7-x (YBCO) film on buffered metal tapes, we have to fire films below 800°C and avoid formation of BaF 2 in the films which leads to low J c by metalorganic deposition using trifluoroacetate method. By estimating each process condition to reaction rate of fluorides with water vapor in precursor, we can established firing profile for YBCO film on buffered metal substrate at 725°C. With the profile, we can successfully obtained YBCO film on CeO 2 /YSZ/hastelloy, which has critical current density (J c ) of 1.72 MA/cm 2 (77 K, 0 T) and thickness of 1860 A.

Angle-resolved photoemission study of insulating and metallic Cu-O chains in PrBa2Cu3O7 and PrBa2Cu4O8

We compare the angle-resolved photoemission spectra of the hole-doped Cu-O chains in PrBa2Cu3O7 (Pr123) and in PrBa2Cu4O8 (Pr124). While, in Pr123, a dispersive feature from the chain takes a band maximum at k(b) (momentum along the chain) approximately pi/4 and loses its spectral weight around the Fermi level, it reaches the Fermi level at k(b) approximately pi/4 in Pr124. Although the chains in Pr123 and Pr124 are approximately 1/4 filled, they show contrasting behaviors: While the chains in Pr123 have an instability to charge ordering, those in Pr124 avoid it and show an interesting spectral feature of a metallic coupled-chain system.

Synthesis and superconducting properties of (Y1−xPrx)Ba2Cu4O8 and (Y1−xPrx)2Ba4Cu7O15−y compounds

Abstract Both (Y1−xPrx)Ba2Cu4O8 (hereafter abbreviated as Y/Pr124) and (Y1−xPrx)2Ba4Cu7O15−y (Y/Pr247) compounds were successfully synthesized over the whole concentration range 0≤x≤1 by means of either hot isostatic pressing (HIP) technique or high pressure oxygen gas technique. We revealed that the superconducting transition temperature disappears at xc=0.8 in both systems in contrast to xc=0.5 for the (Y1−xPrx)Ba2Cu3O7 (Y/Pr123) system reported in the literature and concluded from this that the suppression of superconductivity due to the Pr-doping is weaker in both 124 and 247 systems than that in the 123 system. Furthermore, a combination of the magnetic susceptibility data in the normal state with the Pr–O distance derived from the neutron diffraction experiments led us to conclude that the Pr ion is in the trivalent state for all samples in both 124 and 247 systems. An increase in the critical concentration xc in the Y/Pr124 and Y/Pr247 systems relative to that for the Y/Pr123 system is attributed to an increase in the hybridization of the Pr-4f and O-2p orbitals.

Preparation of bi-axially aligned YBa2Cu3O7−δ film on CeO2-buffered MgO by chemical solution deposition

Abstract We have succeeded in preparing in-plane aligned YBa 2 Cu 3 O 7− δ (Y123) film by chemical solution deposition (CSD) processing on CeO 2 (100)-buffered MgO (100) substrates. The CeO 2 buffer film was deposited on MgO (100) single crystalline substrate by pulsed laser deposition (PLD). For CSD coating, a homogeneous coating solution having a molar ratio of Y:Ba:Cu=1:2:3, was prepared by dissolving metal naphthenates in toluene. This solution was spin-coated both on the YSZ (100) and on the CeO 2 -buffered MgO (100) single crystalline substrates. The precursor films were calcined at 425°C and fired at various temperatures under low oxygen partial pressure ( p O 2 ). All Y123 films showed strong (00 n ) peaks, which correspond to c -axis orientation perpendicular to the substrates and their a / b -axes were in-plane aligned. We confirmed that CeO 2 buffer is usable for CSD processing. While the Y123 films on the YSZ reacted with the substrate forming BaZrO 3 phase and did not show sufficient superconducting properties. The T c,zero value of the Y123 film prepared on CeO 2 -buffered MgO substrate was 91.5 K and J c was 1.2×10 5 A/cm 2 at 77 K, 0 T.

Microstructure of TFA-MOD superconductor film on metal tape

Superconductor film of YBa2Cu3O7� d having high-Jc values was formed on a CeO2/YSZ buffered metal tape by the metal-organic deposition using trifluoroacetates (TFA-MOD) method. Transmission electron microscopy (TEM) confirmed the presence of microstructures of multi-layered structure of YBCO/CeO2/YSZ/Ni-based alloy. The thickness of each thin film YBCO, CeO2 and YSZ, was estimated to be 0.2, 0.5 and 1.3 lm, respectively. Both the film of YSZ on polycrystalline and the film of CeO2 on the YSZ film were composed of columnar grains aligned h 100 i direction. The columnar structure of the CeO2 film was strongly correlated to that of the structure of YSZ film. While highly oriented YBCO film was formed on the CeO2 film, it was not dense and had a rough surface. TEM-EDS revealed copper oxide in the film of YBCO and secondary phase produced from YBCO and CeO2 (BaCeO3) between the two layers. 2002 Elsevier Science B.V. All rights reserved.

Preparation of YBCO films on CeO2 buffered metallic substrates by the TFA-MOD method

Abstract Biaxially aligned YBa 2 Cu 3 O 7− y (YBCO) coated conductors on long metallic substrates are required for power applications. Recently trifluoroacetate-metal organic deposition (TFA-MOD) has been well-known as the most prospective method for the preparation of high J c YBCO films and it has been applied on metallic substrates. We optimized the deposition condition of the CeO 2 films on IBAD tapes and fabricated 10 cm class in-plane textured CeO 2 buffered IBAD tapes by the PLD method. We prepared YBCO films on CeO 2 buffered IBAD tapes by the TFA-MOD method. The YBCO films deposited on the buffered tapes were out of plane and in-plane aligned. The J c value for short sample was 1.72 MA/cm 2 at 77 K, 0 T. These results suggest that the CeO 2 buffered IBAD tapes are feasible for the substrate for YBCO coated superconducting wire by the TFA-MOD method.

YBa2Cu3O7−δ deposition on Ni–Cr alloy tape by liquid phase epitaxy method

Abstract Thick YBa 2 Cu 3 O 7− δ (YBCO) films have been successfully formed by the liquid phase epitaxy (LPE) method on Ni–Cr alloy tape. A buffer layer of yttria stabilized zirconia and seed layer of YBCO were formed by the ion beam assisted deposition and by the pulsed laser deposition method, respectively. YBCO films have been grown from the solution of BaO–CuO–Ag–BaF 2 at 820, 845 and 860 °C under low oxygen partial pressure of 2% to prevent the metallic substrate from reacting with the solution. Good YBCO films are obtained by the growth at 820 °C, and the best one shows high critical current density of 1.9 MA/cm 2 . A cross-sectional observation by high resolution scanning electron microscopy shows neither reaction layer nor damaged region at the substrate/YBCO film interface. θ –2 θ and pole figure X-ray diffraction of the seed layer and the YBCO LPE layer show that in-plane orientation distribution is highly improved by the LPE process.

YBCO thin films on multilayers prepared by all-chemical solution deposition processing

Abstract The chemical solution deposition (CSD) technique has been applied to prepare both YBa 2 Cu 3 O 7− δ (YBCO) and buffer layers on a YSZ substrate. Y 2 O 3 and CeO 2 were employed as the buffer layers, and it was confirmed that they grew epitaxially by the CSD method. Cross-sectional transmission electron microscope observations revealed that Y 2 O 3 grew up to the top of the film. Furthermore, the YBCO film on the Y 2 O 3 or CeO 2 /Y 2 O 3 layers were c -axis aligned and showed a good in-plane alignment. The transition temperature and the critical current density of the YBCO/Y 2 O 3 /YSZ multilayer were 89 K and 4×10 4 A/cm 2 at 77 K, 0 T, respectively.

Effect of Zn substitution on the one-dimensional metallic behavior of PrBa2Cu4O8

Abstract We have grown PrBa2(Cu1−xZnx)4O8 single crystals with nominal compositions of x=0, 0.05, 0.10, and 0.15, and measured the resistivity along a- and b-axis directions. For the Zn-free sample, the conduction along the b-axis direction was highly metallic, which persisted up to the x=0.15 sample although the doping of Zn increased the resistivity. On the other hand, the a-axis resistivity of the Zn-free crystal exhibited a peak around 130 K, which is attributable to a switching of the dominant conduction path from the Cu–O chain site at low temperature to the CuO2 plane at high temperature. With Zn doping, the peak moves to lower temperature and the resistivity extrapolated to T=0 increases, indicating that Zn doping suppresses the coherent conduction across Cu–O chains.