Takuo Takeshita

Phase relation and heat capacities of Ba2YCu3O7−x at high temperature

Abstract The heat capacities of Ba 2 YCu 3 O 7− x ( x = 0.18, 0.35, and 0.60) were measured in the range from room temperature to 860 K by an adiabatic scanning calorimeter. X-ray diffraction analyses were also performed on the quenched and annealed samples. No heat capacity anomaly was seen in either orthorhombic(I) Ba 2 YCu 3 O 6.82 or tetragonal Ba 2 YCu 3 O 6.40 . For Ba 2 YCu 3 O 6.65 , the heat capacity anomaly was observed above 700 K, which was correlated with the phase transition from orthorhombic(I) to orthorhombic(II) structure. The phase relations among orthorhombic(I), orthorhombic(II), and the tetragonal phases were also clarified.

Preparation and Characterization of (Y, Gd)1Ba2Cu3Ox Thin Films

Thin films of the oxide superconductor (Y,Gd)BaCuO system on MgO(100) substrates were prepared by Facing Targets Sputtering (FTS) deposition method. These thin films possess the following properties ;Y-Ba-Cu-O(YBCO) thin film has Tc(0)=72[K], Jc(at 4.2[K])=6.2 × 106[A/cm2] ; Gd-Ba-Cu-O(GBCO) thin film has Tc(0)=58[K], Jc(at 4.2[K])=2.2 × 105[A/cm2] ; (Y,Gd)-Ba-Cu-O ((Y,G)BCO) thin fim has Tc(0)=69[K], Jc(at 4.2[K])=3.2 ×105[A/cm2]. Current-voltage characteristics of these thin films are as follows ; YBCO thin film has define hysteresis, (Y,G)BCO thin film’s critical current(Ic) drops in I-V curve with micro-wave irradiation.

Bi Based Oxide Superconducting Thin Film Prepared by CVD Method

BiSrCaCuO superconducting thin films were prepared on MgO (100) substrates by metal organic chemical vapor deposition (MOCVD) using Bi(ph)3, Sr-, Ca-, Cu(DPM)2, and effects of deposition parameters (substrate temperatures (Ts), oxygen flow rates (FO2) and cooling rates (C.R)) were investigated with regards to superconducting properties of films. A film as prepared at Ts=800°C, in FO2=200ccm, and with C.R=15°C/min possesses the (2212) structure. This film shows a micro mosaic structure with c-axis orientation perpendicular to the substrate, and has zero-resistance temperature of 72K.

High-Tc Superconducting Bi-Ca-Sr-Cu-O Thin Films Prepared by Metalorganic Deposition (MOD)

High-Tc superconducting Bi-Ca-Sr-Cu-0 thin films were prepared by the spin-on pyrolysis technique using a mixed solution of 2-ethγlhexanoates of constituent metals dissolved in an organic solvent. Effects of the pyrolyzing temperature were investigated, and it was found that the films prepared by pyrolyzing as-deposited organometals at 1073K showed superconductivity without further heat treatment. X-ray diffraction examinations of these films showed that the crystallographic c-axis was oriented perpendicularly to the film surface. The superconducting transition temperature of these films observed was Tc = 90K(onset) and 77K(end).