Shui-sheng Jiang

Effects of low-energy neutron irradiation on Bi-based superconductors

Abstract Bi-based and Sn-doped Bi-based superconductors were subjected to low-energy neutron irradiation. Experimental results showed that J c of irradiated Bi-based sample was increased by 30%, and T c of irradiated Bi-based and Sn-doped Bi-based samples were increased by 2.5–5.0 K. The low-energy neutron irradiation was also found to decrease the normal state resistivity of samples. Therefore, low-energy neutron irradiation is a useful method to improve the superconductivity of Bi-based materials. The reasons for the improvement of T c , J c and normal state resistivity by low energy neutron irradiation were discussed.

Microstructures of La1.85Sr0.15CuO4 doped with Ni at high doping level

Abstract Ceramic superconductors of La 1.85 Sr 0.15 Cu 1− y Ni y O 4 with 0.00 ≤ y ≤ 0.50 were synthesized. There is no impurity phase detected in the entire Ni doped region. The structure of these Ni-doped samples was characterized by X-ray diffraction studies. The atomic structural parameters were obtained by Rietveld refinements for the Ni-doped samples with y ≤ 0.50. Some meaningful bond distances were determined according to the refined results. According to the variations of some bond distances with y , the whole doping range could be divided into two regions: low doping level (LDL) and high doping level (HDL). The bond length between the two apical oxygen atoms in the CuO 6 octahedra for the Ni-doped samples increased with increasing content of Ni in the LDL, and decreased in the HDL. The average bond distance of LaO was not changed in the whole doping region. The metal-insulator transition was also observed in this Ni-doped system.

Orientation Distribution of Grain Planes in Polycrystal Ag/Bi-2223 Tape

For polycrystalline Ag/Bi-2223 tapes, the preferential orientation of grains is a very important issue. The platelike grains in the tapes are generally believed in a high-order alignment. However, microstructural observation by SEM shows that the grain alignment is far from perfect. Theoretically, upper critical field, Hc2, for H parallel to ab plane and c axis was calculated form the relation of M(H). However, the ratio of Hc2 (H//ab) to Hc2(H//c) depends on the angle (θ) between the ab plane of grains and the broad surface of the tapes. Based on the ratio, the orientation distribution of grains is obtained. The results show that grains in Ag/Bi-2223 tapes can grow with ab plans at any angle between 75° > θ > −75°, but no grain can grow with its ab plane perpendicular to the tape broad surface. The overall distribution is that: >90% grains orient in the angle range of |θ| < ± 75°, about 5% grains at ±75° ≤|θ| ≤ ±85°, and no grains at |θ| > ±85°.

Structure and Superconductivity of the Y4Ba8Cu12O27 Nanosuperconductor

A nanosuperconductor was prepared and characterized in the present work. The nanosuperconductor consisted of nanocrystals with superconducting transition temperature, Tc, of 88 K. Dimension of the nanocrystals is dozens nm in diameter and hundreds nm in length. The compound of the nanocrystals has a formula of Y4Ba8Cu12O27. The structure of the nanocrystals was found to be an orthorhombic perovskite, and the lattice constants were determined as a = 7.634 Å, b = 7.758 Å, and c = 11.654 Å, respectively.

Development of Twins in YBa2Cu3Oy Superconductor

It is significant to study the problems how the tetragonal and orthorhombic structures of YBa2Cu3Oy generate, since the structures closely relate to superconductivity. To deal with these problems, we approach the generation of tetragonal and orthorhombicity and their morphologies by SEM, TEM, and X-ray diffraction analysis, respectively. For interpreting the experimental phenomena, we put forward a crystal growth modal: the tetragonal grows at sintering temperatures, and the tetragonal transits to orthorhombicity and forms twins along [110] faces at annealing temperatures. This model agrees with experimental results well.

Superconducting and structural effects of grinding upon YBa2Cu3Oy

Abstract Samples of YBa 2 Cu 3 O y superconductor were ground for 0, 1, 4, 16, 28, 36, and 100 h, respectively. The grinding upon sample was performed for 2–6 h every day and ground samples were kept nature state in air for the rest hours. The appearance was observed, AC susceptibility and critical temperature of the ground samples were measured. The appearance and superconductivity of the ground samples were continuously damaged as the grinding time increased. However, for the sample ground for 36 h, that crystal radii increased and superconductivity improved anomalously was observed experimentally. The experimental results showed that on keeping the nature state the damaged crystal cells regrew and superconductivity was recovered at room temperature.

The flux pinning potential of Ag/Bi-2223 tapes for H//c-axis

Abstract Flux pinning potential U(T,H) of Ag/Bi-2223 tapes has been determined through measurements of transport current density J(T,H) in applied magnetic field from 0 to 3T and at temperature from 23K to 77K. The field was perpendicular to the broad surface of the tape. Generally, U(T,H) and J(T,H) are regarded as U(T,H) = U(T)U(H) and J(T,H)=J(T)J(H), respectively. U(T,H) can be obtained by fitting the function of J(T,H) if a proper theory of flux dynamics would be used. In the case of transport current density, the experimental J(H) is found to be linear with lnμoH, that conforms to Andsons flux dynamics theory. By using the theory, the pinning potential U(T,H) for Ag/Bi-2223 tapes is determined and formulated quantitatively. The resulting flux pinning potential U(T,H) is shown in a three dimension diagram.