Yoshikazu Hidaka

Anisotropie Properties of Superconducting Single-Crystal (La1-xSrx)2CuO4

Anisotropic electrical properties of single crystals of the recently-discovered superconducting La-Sr-Cu-O system are described. The resistivity along the c-axis of the K2NiF4 structure is 1.9×10-2 ohm-cm, 20 times larger than that along the a-axis. The second critical magnetic field Hc2 along the a-axis is estimated to be larger than that along the c-axis by a factor of more than 5. The results strongly indicate that the oxide system can be regarded as a pseudo-two-dimensional superconductor.

Single crystal growth of (La1-xAx)2CuO4 (A=Ba or Sr) and Ba2YCu3O7-y

Single crystal growth using the CuO flux method is presented in this paper. (La1-xAx)2CuO4 (A = Ba or Sr) single crystals with a maximum size of about 8×8×2 mm3 were grown from a molten oxide compound of (La1-xAx)2CuO4 (20 mol%) and CuO (80 mol%) at about 1140°C. Also, Ba2YCu3O7-y single crystals of about 1×2×0.1 mm3 were grown by a similar flux method. As-grown crystals were superconducting, and their transition temperatures were raised by annealing in oxygen.

Anisotropy of the Upper Critical Magnetic Field in Single Crystal YBa2Cu3O7+y

The upper critical magnetic field Hc2 was measured on single crystals of the recently-discovered superconducting YBa2Cu3O7+y oxide. The Hc2 along the basal plane is estimated to be larger than that along the c-axis by a factor of 5. A small anisotropy of Hc2 in the basal plane is also found. It is not clear at present whether this small anisotropy is intrinsic or due to crystal imperfectness such as micro-twinnings.

Deformation of Iron Oxides upon Tensile Tests at 600–1250°C

Tensile tests of virtually “pure” FeO, γ -Fe3O4, and α-Fe2O3 were performed at 600–1250°C at strain rates of 2.0×10−3–6.7×10−5 s−1 under controlled gas atmospheres. Mechanical properties and deformation/fracture behavior were investigated. For α-Fe2O3, brittle fracture resulted at 1150–1250°C, and the fracture strain was below 4.0% at a strain rate of 2.0×10−4 s−1. Oxide of γ -Fe3O4 deformed plastically above 800°C. Steady-state deformation was indicated at 1200°C; elongation of 110% was obtained. Plastic deformation observed at 800–1100°C was considered to result from dislocation glide. Using TEM, burgers vector of dislocation observed in deformed γ -Fe3O4 was determined to be 〈110〉, and its slip system was estimated to be {111}<110>. Oxide of FeO deformed plastically above 700°C. Steady-state deformation became predominant above 1000°C. Elongation of 160% was obtained at 1200°C. Strain rates of FeO at 1000 and 1200°C were proportional to the fourth power of the saturated stress, indicating that the plastic deformation was affected by dislocation climb.

Single Crystal Growth of Ba2NdCu3O7-δ from BaCO3-Nd2O3-CuO Solution

Four to five mm square Ba2NdCu3O7-δ single-crystal plates were grown by slow cooling of a CuO-rich BaCO3-Nd2O3-CuO solution maintained at 1000 to 1200°C. Thin platelets and cube-like crystals of mm size were also prepared. This crystal size improvement is attributed to the fact that Ba2NdCu3O7-δ has the highest thermal stability among superconducting oxides Ba2RCu3O7-δ (R=Y and lanthanoids).

Tensile Deformation of Iron Oxides at 600–1250°C

Tensile tests of virtually “pure” FeO, γ -Fe3O4, and α-Fe2O3 were performed at 600–1250°C at strain rates of 2.0×10−3–6.7×10−5 s−1 under controlled gas atmospheres. Mechanical properties and deformation/fracture behavior were investigated. For α-Fe2O3, brittle fracture resulted at 1150–1250°C and the fracture strain was below 4.0% at a strain rate of 2.0×10−4 s−1. γ -Fe3O4 deformed plastically above 800°C. Steady-state deformation was indicated at 1200°C; elongation of 110% was obtained. Plastic deformation observed at 800 to 1100°C was considered to result from dislocation glide. Using TEM, the Burgers vector of dislocations observed in deformed γ -Fe3O4 was determined to be <110>, its slip system was estimated to be {111}<110>. FeO deformed plastically above 700°C. Steady-state deformation became predominant above 1000°C. Elongation of 160% was obtained at 1200°C. Strain rates of FeO at 1000°C and 1200°C were proportional to the fourth power of the saturated stress, indicating that plastic deformation was affected by dislocation climb.

ANISOTROPIC UPPER CRITICAL MAGNETIC FIELD IN SINGLE CRYSTAL Ba2YCu3O7-y

Abstract The upper critical magnetic field Hc2 of Ba2YCu3O7−y has been measured using single crystals with applied fields up to 26T. The results exhibit strong anisotropy with regard to the c-axis and the basal plane. The slope of temperature dependence of Hc2 along the c-axis is -0.56T/K, while that along the basal plane is -3.3 to -2.6T/K. Hc2(0) for the c-axis and basal plane are estimated to be 35T and 160 to 210T, respectively, using the Werthamer-Helfand-Hohenberg theory. From these values, the coherence length along the c-axis is estimated to be 5.1 A, and that in the basal plane is 31 A. The former value is comparable to the lattice constant c.

High Tc superconducting single crystal Eu1Ba2Cu3Oy

Single crystals of Eu1Ba2Cu3Oy are grown from molten compounds. The crystals are then annealed in an oxygen atmosphere. Measurements are performed to determine the structure and transport properties of the single crystals. The results are orthorhombic symmetry, a twinning structure, high Tc above 90 K and a transition width less than 1 K. Thermal cycling and adsorbed water effects on single crystals are also studied.

Polarizing Microscopic Observation of the Superconducting Eu1Ba2Cu3Oy Crystals

The orthorhombic high-Tc Eu1Ba2Cu3Oy crystals are investigated optically by the polarizing microscope. The crystals are optically anisotropic in the a-b plane, and the phase difference between the advanced- and the retarded-phase axis is 30±3 degrees along the a- and b-axes. According to the reflection formula for metals, the anisotropic conductivity between these two directions is analyzed. The anisotropy of a factor of about 2 is obtained.

Anisotropic Properties of Superconducting Single Crystals (La1-xSrx)2CuO4 and Ba2YCu3O7+y

Resistivity and the second critical field Hc2 have been measured for superconducting (La1-xSrx)2CuO4 and Ba2Cu3O7+y single crystals grown from the melt. The Hc2 along the basal plane is estimated to be larger than that along the c-axis by a factor of more than 5. These anisotropy due to crystallographic structure is briefly discussed.