Yoshihito Abe

Superconducting and magnetic properties of Bi2Sr2Ca1-xYxCu2Oy (0≦x≦1)

Abstract The effect of substitution of Y atoms for Ca atoms has been studied in the Bi 2 Sr 2 Ca 1- x Y x Cu 2 O y compound system. For x x , though the transition temperature of about 85 K is maintained. For x ≧0.5 samples, the electrical resistivity behavior can be well described by the three-dimensional variable range hopping conduction, indicating that the system is essentially insulating. In this range of x , magnetic susceptibility shows spin-glass-type cusp at 13 K in the heating process after zero-field cooling and an enhanced cusp at 11 K in the field-cooling process. In the temperature range above about 150 K the Curie-Weiss dependence holds well with a positive paramagnetic Curie temperature, which increases to 40 K with increasing x in the insulating region.

The Dependence of the Superconducting Transition upon the Quench Temperature of YBa2Cu3Oy

The superconducting transition properties have been evaluated for YBa2Cu3Oy compound samples prepared after processing from vairous quench temperatures following a sintering stage at 880°C. Two sets of temperatures depicting the onset of the superconducting transition have been observed. One set is found to cover 79-94 K for samples with orthorhombic symmetry, and the onset temperature increases as the quench temperature is lowered. The other set is found to cover the range 52-58 K for samples with tetragonal symmetry.

Study on copper valency of high-tc superconductor YBa2Cu3O7−y by high temperature X-ray absorption spectroscopy

Abstract The X-ray absorption spectra of the Cu K-edge have been obtained for a high-T c superconductor YBa 2 Cu 3 O 7−y by in-situ high temperature measurements between room temperature and 600 °C and for quenched samples prepared by rapid cooling from various temperatures up to 880 °C. The results indicate that the copper valency is predominantly 2+ and the monovalent state appears as the oxygen contents decrease with increasing temperature. The Cu K-edge X-ray absorption spectra of lanthanoide compounds with oxygen-deficient triperovskite structure, LnBa 2 Cu 3 O 7−y (Ln=Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu) were also reported.

Superconductivity and Crystal Structure of LaBa2Cu3-xOy Compounds

An extensive study of magnetic, electrical transport, and structural properties of the normal and superconducting states of LaBaCuO2BO3 are presented. A ceramic compound of LaBaCuO2BO3 has been synthesized by the solid-state reaction technique under ambient pressure by reacting BaCO3, La2O3, CuO and B2O3. LaBaCuO2BO3 compound was characterized by x-ray diffraction and scanning electron microscope-x-ray energy dispersion spectrum analyses. Rietveld refinement of powder x-ray diffraction data indicated that the compound is P4bm space group symmetry and a=5.57475(8), c=7.5056(l)A. Measured magnetic susceptibilities of powder specimens of LaBaCuO2BO3 compound indicate a transition to a diamagnetic state at 32 K.

Study of the Infrared Properties of (La1-xSrx)2CuO4

Reflectivity and transmission spectra of (La1-xSrx)2CuO4 were measured in the spectral range of 20-4800 cm-1. The intensity of the absorption peak around 255 cm-1 became twice with lowering temperature from 298 to 19 K accompanying weak softening, while the Cu-O asymmetric stretching mode at 510 cm-1 was almost unchanged both in its energy and intensity. The origin of the soft-phonon mode is discussed.

Superconductivity of (La1−xSrx)2CuO4−γ (0≦χ≦0.03)

Abstract The dependence of the fractional volume of an apparent superconductor, its transition temperature and paramagnetic susceptibility on the strontium concentration χ is studied in (La 1−x Sr x ) 2 CuO 4−θ for the small region of χ (0 ≦χ≦0.03). Superconductivity observed in undoped La 2 CuO 4−γ compound disappears at χ = 0.01 together with the disappearance of the antiferromagnetic phase. The origin of this superconductivity is discussed taking account of the anomalous property, i.e., the Meissner effect is larger than the shielding effect. The phase diagram of (La 1−x Sr x ) 2 CuO 4−γ is interpreted from a phenomenological crude model based on weakly localized holes around oxygen sites in the CuO 2 plane.

93Nb and 35Cl nuclear quadrupole resonance in the low temperature modification of niobium pentachloride

Abstract 93 Nb and 35 Cl NQR in the low temperature modification of niobium pentachloride have been examined from 4.2 K to 440 K, where the signal disappeared. The resonance frequencies and their temperature dependences are compared with those in the high temperature modification from the view point of bond character.

Superconducting properties and phonon spectra of Bi2Sr2Y1−xCaxCu2Oy

Abstract The phase diagram observed for Bi 2 Sr 2 Y 1−x Ca x Cu 2 O y compounds shows good coincidence with that of the La Sr Cu O system when Tc is normalized by the maximum value and plotted against the hole density per CuO 2 plane. All doped holes are found to be mobile. Phonon spectra were investigated for all samples and compared with the results of Ba 2 YCu 3 O 7−y leading to the assignment of the phonon modes.

Temperature dependence of 14N NQR in 1,2-diformylhydrazine

Abstract 14 N NQR in 1,2-diformylhydrazine has been investigated between 4.2 and 390 K. The temperature dependence of the electric field gradient was interpreted by taking into account the back donation of the delocalized nitrogen π-electron besides the librational molecular motions.

Fine structure of bromine NQR in the orthorhombic phase of niobium pentabromide

Abstract A spectrum consisting of two singlet and two doublet lines has been found. As possible symmetry elements in the dimer, m and C2 are deduced.