Hiromi Unoki

Phase-Equilibrium Diagram in the Ternary System Y2O3-BaO-CuO

A phase-equilibrium diagram of the ternary system of Y2O3-BaO-CuO was investigated. The temperature vs concentration diagrams are given on four binary systems ranging from YBa2Cu3O7-y to CuO, to BaCuO2·3CuO, to 3BaCuO2·4CuO and to 3BaCuO2·2CuO mixtures. A liquidus line required for the preparation of YBa2Cu3O7-y single crystal from solution was found to be extremely narrow in concentration range.

Phase Diagram and Crystal Growth of Superconductive (NdCe)2CuO4

Single crystals of (NdCe)2CuO4 have been grown by the travelling-solvent floating-zone (TSFZ) method. The single crystal grown in a deoxidized atmosphere exhibits superconductivity. Part of the crystallographic phase diagram of the Nd2O3-CuO system has been derived by conventional means to determine the concentration and temperature range of the liquidus line.

Quadrupolar response and rotational invariance of singlet ground state system; HoVO4

Elastic properties of holmium vanadate, HoVO 4 , have been investigated by means of an ultrasonic method. The elastic constants C 11 , ( C 11 - C 12 )/2 and C 66 exhibited remarkable softenings possessing minimum points around 13.5 K, which are characterized by the quadrupolar responses for the singlet ground state system. Appling magnetic fields along the tetragonal c -axis, the elastic anomalies of ( C 11 - C 12 )/2 and C 66 associated with the level crossing of the singlet ground state at about 10.6 T have been found. The rotational invariance effect has been revealed in the C 44 mode under magnetic fields along c -axis.

Phase Diagram of the La2O3-CuO System and Crystal Growth of (LaBa)2CuO4

Single crystals of (LaBa)2CuO4 were grown by the top-seeded solution growth (TSSG) method. A crystallographic phase diagram of the La2O3-CuO system was derived by means of differential thermal analysis, quenching technique and X-ray diffraction.

Field-induced pinning effect of Nd(Ba1−xNdx)2Cu3O7−δ single crystals grown by the traveling-solvent floating-zone method

We have studied the superconducting properties of Nd(Ba1−xNdx)2Cu3O7−δ (Nd123, x ≈ 0.1) single crystals grown by the traveling-solvent floating-zone method under 0.1% O2 in Ar atmosphere. The enhancement of the magnetization with increasing field is observed in the hysteresis (M-H) loop in fields both parallel and perpendicular to the c-axis of the Nd123 single crystals as well as in the bulk crystals prepared by the oxygen-controlled-melt-growth (OCMG) method. The composition variation of Ba/Nd is observed in the matrix of Nd123 crystals by an analytical TEM equipped with a cold field-emission gun. It turns out that the enhancement is due to the field-induced pinning effect ascribed to the weak superconducting NdBa substitution regions in the Nd123 matrix.

Primary crystallization fields and crystal growth of YBa2Cu3O7-y and NdBa2Cu3O7-y

The phase diagrams of the systems Y2O3-BaO-CuO and Nd2O3-BaO-CuO have been studied. The liquidus and solidus lines were determined by differential thermal analysis (DTA), quenching experiments and X-ray diffraction. Single crystals of RBa2Cu3O7-y were grown from high-temperature solutions by slow-cooling, top-seeded solution growth (TSSG) and travelling-solvent floating-zone (TSFZ) method with BaO and CuO as the flux.

Crystal growth of La2−xSrxCuO4−δ by the travelling-solvent floating-zone method

Abstract The crystal-growth conditions for La 2−x Sr x CuO 4− δ by the travelling-solvent floating-zone method have been investigated. The effect of the ambient atmosphere on the growth has been studied. Results show that evaporation of components from the floating zone is very low and does not significantly influence the growth procedure. However, high oxygen ambient pressure can lead to formation of second phases like LaCuO 3 . The composition and amount of solvent were also investigated. It is shown that the density and porosity of the starting feed material are the crucial variables for a successful growth procedure. The “twice-scanning” method has been chosen to achieve stable growing processes at low growth rate. The characterization of as-grown crystals by DC susceptibility, rocking X-ray curve and electron-probe microanalysis (EPMA) measurement is reported.

Polarized X-Ray Absorption Fine Structure of La2CuO4-y Single Crystal

Polarized Cu K X-ray absorption fine structure (XAFS) has been measured on a single crystal of undoped La 2 CuO 4- y for the first time, using a fluorescence detection technique. The polarized near-edge structure and EXAFS were strongly anisotropic, demonstrating the quasi-two-dimensional nature of electron states and local structure. The polarization dependence of the near-edge structure confirms that the Cu atoms take 2+ valence or d 9 configuration with a strong fourfold Cu–O1 bonds within the CuO 2 plane and weak twofold Cu–O2 bonds along the c -axis, which is consistent with the anisotropic local structure suggested by the Fourier transform of polarized EXAFS and a crystal structure.

Phase Diagram and Crystal Growth of NdBa2Cu3O7-y

The phase diagram of a binary system between NdBa2Cu3O7 and 3BaCuO22CuO has been studied. A liquidus line which is favourable for obtaining NdBa2 Cu3O7 single crystals from solution is found to exist in a rather wide range compared with that of YBa2Cu3O7. Single crystals of NdBa2Cu3O7-y have been grown by both the slow-cooling method and the top-seeded solution growth (TSSG) method, in accordance with the obtained phase diagrams of the NdBa2Cu3O7-3BaCuO22CuO system and our earlier Y2O3-CuO-BaO system.

Antiferromagnetism and Superconductivity of La2CuO4

Magnetic susceptibility and electrical resistivity have been measured for stoichiometric and La deficient La2CuO4, and 57Fe doped La2CuO4. In all the samples the magnetic susceptibility shows two cusps around 220 and 110 K. From the temperature dependence of resistivity R(T) and the Mossbauer effect of 57Fe doped in La2CuO4, it is concluded that the cusp of susceptibility at 220 K corresponds to the antiferromagnetic transition. The slope of resistivity |dR/dT| becomes small below this temperature with decreasing temperature. The hyperfine field of iron is 395 kOe at 77 K. The La deficient sample exhibits superconductivity below 35 K.