Yoshinobu Takano

Fluctuation conductivity analysis in Zn-doped YBa2Cu3O7 and related systems

Fluctuation conductivity σ(e) above Tc as a function of the reduced temperature e was measured in polycrystalline YBa2Cu3O7 and LaBaCaCu3O7 with Zn doping. The results for σ(e) are analyzed in terms of the Aslamazov-Larkin theory for a layered superconductor in which effect of d-wave pairing as well as that of short-wavelength cutoff is taken into account. The d-wave character appears in the σ(e) formula as renormalization effects on the fluctuation amplitude and the reduced temperature. Good agreement is attained between theory and experiment even in a high e region, which allows us to discuss the doping dependence of the fluctuation amplitude and the out-of-plane coherence length. The d-wave nature could be responsible for the doping dependence of the fluctuation amplitude.

Resistive transition behavior of impurity-doped YBa2Cu3O7 type superconductors

Abstract Critical behavior in resistivity above T c for several impurity-doped YBa 2 Cu 3 O 7 type superconductors was investigated. These include 1) oxygen-controlled YBa 2 Cu 3 O 7−y , 2) YBa 2 (Cu 1− x Zn x ) 3 O 7 , 3) La 1− z Pr z Ba 2 Cu 3 O 7 and 4) Ag p (YBa 2 Cu 3 O 7 ) 1− p composites. The experimental data were analyzed in terms of a power law following the Aslamazov-Larkin theory. The amplitude C F of the power law changes systematically with increasing dopant level: C F increases with y or z while it decreases with x or p . We discuss roles of the dopant for each system in the fluctuation regime.

Preparation and characterization of PEG/Bi2212 nanocomposites

Single-phase nanocomposites of Bi2Sr2CaCu2O8+d (Bi2212) with organic polymer have been successfully synthesized for the first time by the foliation-adsorption technique. Colloidal suspension containing exfoliated Bi2212 nanosheets was prepared with a stepwise intercalation method. Poly(ethylene glycol) (PEG) was slowly added into colloids containing Bi2212 nanosheets. X-ray diffraction patterns show that the gallery height of Bi2212 host is expanded from 3.08 nm to 4.91 nm in PEG/Bi2212 nanocomposites. The basal plane expansion of 0.9 nm is in good agreement with the values reported for PEG-containing nanocomposites, suggesting that a PEG bilayer is incorporated within the Bi2212 nanosheets.

Synthesis and characterization of alkylammonium/Bi2212 nanohybrids

Single-phase nanohybrids of Bi2Sr2CaCuO8+d (Bi2212) with alkylammonium salts have been synthesized for the first time by a stepwise intercalation method. To increase the gallery height between the Bi-0 layers of Bi2212 crystal, intercalated precursor was prepared by the chemical vapor transport technique with Bi2212 and HgBr2 in a sealed quartz ampoule. Then, n-dodecyl trimetylammonium bromide (DTA:Br) or n-hexadecyl trimethylammonium bromide (HTA:Br) was intercalated into HgBr2/Bi2212 via ion exchange method. Nanohybrids were characterized by powder X-ray diffraction (XRD). There was no trace of the pristine phase in XRD patterns for all nanohybrids, indicating that DTA or HTA ion is incorporated homogeneously into each Bi2212 layer It is found that the gallery height of Bi2212 host is expanded from 3.08 run to 8.22 run (?c = 5.14 nm) in HTA/Bi2212 nanohybrid. HTA/Bi2212 nanohybrid was exfoliated into single layers in acetone. A transparent colloid is found to be stable for 5 days after ultrasonication.

Structural Studies of Layered Magnetic Semiconductor (La1−xCaxO)Cu1−xNixS

Crystal structure of layered magnetic semiconductors (La1−xCaxO)Cu1−xNixS which show ferromagnetism even at room temperature has been investigated precisely using synchrotron x‐rays to understand their physical properties from a view point of the crystal structure and check magnetic impurities. No magnetic impurities were found and this means that these ferromagnetic characters are intrinsic properties. Precise structural analysis indicate that the interlayer distance between S‐Cu2‐S and La‐O2‐La layers decreases with increasing concentration x. The increase of x leads to reduce the electrical resistivity. From these results, the interaction between LaO and CuS layers is therefore important in controlling the physical properties of these compounds.