He Aisheng

Fabrication, characterization and welding of Bi(Pb)-Sr-Ca-Cu-O superconducting fibres

Superconducting fibres of Bi(Pb)-Sr-Ca-Cu-O high Tc superconducting materials have been prepared by means of the laser-heated pedestal growth (LHPG) method. The highest zero resistance temperature Tco reached is 114 K, and the highest critical current density Jc (77 K, 0 T) is greater than 5000 A cm-2. As-grown superconducting fibres were successfully fabricated without post-growth heat treatment. Amorphous materials were used for the first time to make high quality fibres. The strong textured structure and highly aligned morphology of the fibres were studied. The influence of growth conditions, thermal treatment and the composition of the fibres was also discussed.

Ultrasound anomalies in single phase (Bi1-xPbx)2Sr2CanCun+1O2n+6+y superconducting ceramics

Ultrasonic anomalies near 200 K in single-phase (Bi1-xPbx)2Sr2CanCun+1O2n+6+y (x=0-0.2, n=1, 2) superconducting samples were observed by velocity and attenuation measurements of both longitudinal and transverse sound waves. The remarkable isothermal-like anomalous changes near 200 K indicate that there are possible structural changes or phase transitions in the samples. On comparison with YBa2Cu3O7-y, the different behaviours in ultrasonic anomalies are attributed to the differences in structure. It is suggested, however, that the lattice instability appearing near T approximately=2Tc may be a common feature of the existing superconducting perovskites and may have some relation to their high Tc.

Bi-based superconducting fibers prepared from amorphous materials

Bi-based superconducting fibers have been prepared from amorphous materials by the LHPG method. The onset transition temperature reached is 102 K, and the zero resistance temperature reached is 86 K. The critical current density Jc (77 K, O T) is greater than 5000 A/cm2. Structure analysis indicates that the superconducting fibers have highly aligned morphology with a-axis parallel to the growth direction.

Ultrasonic investigations of the layered perovskite ceramic superconducting systems

Ultrasonic measurements have been carried out on three type high T c perovskite ceramic superconductors La-Sr-Cu-O, Y-Ba-Cu-O and Bi(Pb)-Sr-Ca-Cu-O. Anomalies in both sound velocity and attenuation of the above three systems were observed. The elastic constants and the Debye temperatures were also obtained and discussed.

NEUTRON DIFFRACTION STUDY ON (Bi−Pb)2Sr2Ca2Cu3O10

The polycrystalline sample of (Bi–Pb)2Sr2Ca2Cu3O10 with Tc=107 K was prepared. The X-ray diffraction proved that the sample is single phase. The crystal structure study on the sample has been carried out by neutron diffraction. The result shows that its structure is tetragonal body-centre structure with space group of I4/mmm, containing a few oxygen atoms at 4e site in Bi–Pb layers.

Experimental evidence for the lattice instability of Bi-based superconducting systems

Abstract Ultrasonic measurements, specific heat and thermal analysis experiments, X-ray diffraction study and infrared investigation revealed that there are anomalous structural changes or lattice instabilities near 200 K in single 2212 or 2223 phase samples of Bi(Pb)-Sr-Ca-Cu-O system. Detailed study showed that anomalous changes or lattice instabilities are isothermal-like processes and have the characteristics of a structural phase transition, accompanying with increases in lattice constants. Possible mechanism for this lattice instability is discussed.

Preparation, structure and properties of Bi-based superconducting fibers grown by laser-floating-zone-growth method

Abstract In this report, we describes investigation of the preparation, structure and properties of Bi-based superconducting fibers grown (polycrystalline, modifying-composition with self-flux and amorphous material) and varying growth condition have been used. We have got the polycrystalline and single-crystal(or called quasi-single crystal) fibers with Tc value of 83–110K and the most Jc vallue of more than 5200A / cm2. The fibers have a good texture structure i.e., its a-b plane is parallel to the growth direction and c-axis is perpendicular to the influence of growth direction. The growth condition, composition of the source materials and post—growth heat treatment have also been discussed.

Neutron Scattering Study of Sr Substitution for Ba in YBa2Cu3O7-y

Neutron diffraction and inelastic scattering were carried out on YBa2-xSrxCu3O7-y (x=0.5, 1.0, 1.25). It was confirmed that the substitution of Sr for Ba in YBa2Cu3O7-y increases the oxygen vacancies in the Cu O chain. Moreover, the substitution strengthens the coupling between the Ba O plane and the Cu O chain, and reduces the crystal stability. These are the possible causes of Tc depression for Sr substituted YBa2Cu3O7-y.

Bi-BASED SUPERCONDUCTING FIBERS WITH HIGH CRITICAL PARAMETERS

Superconducting fibers of Bi(Pb)-Sr-Ca-Cu-O high Tc superconducting materials have been prepared by means of the laser-heated pedestal growth (LHPG) method. The highest zero resistance temperature T c0 reached is 114 K, and the highest critical current density J c (77 K, 0 T) is greater than 5000 A/cm 2 . As-grown superconducting fibers were successfully fabricated without post-growth heat treatment. Amorphous materials were used for the first time to make high quality fibers. The influence of growth conditions, thermal treatment and the composition of the fibers were discussed.

Structure Refinement of Bi2Sr1.855Ca1.145Cu2O8 from Neutron Data

Neutron diffraction study on the structure of Bi2Sr1.855Ca1.145Cu2O8 was carried out. Data refinements show that the average subcell structure for Bi2Sr1.855Ca1.145Cu2O8 is in the best fit of the space group Fmmm and the structure is described by alternate stacking of SrO-CuO2-Ca-CuO2-SrO slab and a double BiO layers. An oxygen layer sandwiched by the bismuth layers was confirmed.