Yunlong Ge

The influence of growth conditions on the characteristics of Bi-based whiskers

The influence of growth conditions, such as growth time, temperature, Pb doping, the state of the substrate and the growth atmosphere, on the whisker growth have been investigated. It was found that the maximum length of the whiskers is proportional to the growth time at the initial stage; however, after passing a certain growth time, the maximum length stays constant. The high-T(c) phase emerges when the growth time is prolonged for the whiskers whose starting compositions are near the stoichiometry of the high-T(c) phase. The optimum temperatures for whisker growth are in a very narrow range. An appropriate amount of Pb doped into the starting materials and a steady stream of oxygen atmosphere play catalytic roles in the whisker growth.

MORPHOLOGIES AND STRUCTURES OF BI-BASED OXIDE FIBROUS CRYSTALS

Superconducting fibrous crystals which were long enough for the measurements of many physical properties have been prepared by heating an amorphous plate in a steady stream of oxygen. The fibrous crystals have remarkably oriented structures, and their crystal structures are (2212) single phase, and their compositions approach Bi2Sr1Ca1Cu2Ox. The influence of a partially crystallized substrate without Pb doping on the growth of fibrous crystals has also been discussed briefly.

Characteristic study of Bi-based superconducting whiskers and their substrate

Whiskers grown on a substrate are of almost single phases, but the substrate is of multiphase. The whiskers show layered structures, and their composition is homogeneous. The microstructure of the substrate is loose and porous. The growth process of whiskers on the substrate is also discussed briefly.

Structure characteristics of Bi (Pb)-Sr-Ca-Cu-O superconducting whiskers

The crystal structure of superconducting whiskers grown out on the surface of an annealed amorphous plate was studied. The transmission Laue method is used in determining the orientations of the whiskers and examining their perfectness. It was found that the axial direction of a whisker is b-axis (010), and there exist substructures in the whisker.

Crystallization process of Bi(Pb)-Sr-Ca-Cu-O glass

A crystallization study has been carried out for rapidly solidified Bi2Pb0.5Sr2Ca4Cu5Ox glass. Glass transition temperature Tg, crystallized superconducting phases and microstructural changes were measured and analysed by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The crystallization mechanism of the three superconducting phases — (2201) 20 K phase, (2212) 80 K phase, and (2223) 110 K phase — has been discussed, and a time-temperature-transformation diagram for the glass has been constructed.

Microstructures of laser cladded Iron-, Nickel- and Cobalt-Base coatings

Abstract The microstructures of the laser cladded zone for Fe-, Ni- and Co-base coatings are investigated systematically. A long period lamellar carbide (Cr7C3) is found in Fe-base cladded zone, a large amount of dislocations and the Ni3Si phase in Ni-base cladded zone, and a lot of stacking faults in Co-base cladded zone.

AN INVESTIGATION OF MELT-TEXTURED HIGH-TC SUPERCONDUCTOR WIRES MADE BY LASER HEATED PEDESTAL GROWTH TECHNIQUE

Abstract The growth of high Tc oxide superconductors both in Y and Bi systems by the laser floating zone melt technique has been studied. The seeding and feeding rods for the process were prepared by common powder metallurgy. The as-grown crystals are 0.5 –1.5 mm in diameters and show high densities and textured structures with c axis normal to the growth axis which would be greatly helpful to reduce the weak links between grain boundaries and enhance the transport critical current density. High transport Jc of 1880 A/cm2 at 77K and OT was found in Bi2Sr2CaCu2Ox textured fibers and Pb was also added in the specimens in order to raise the Tc and Jc. The samples were also characterized by X-ray diffraction, metallography, TEM, SEM and EPMA.

SOLIDIFICATION CHARACTERISTICS OF YBaCuO COMPOUNDS AND THE TEXTURED CRYSTALS GROWN BY LASER FLOATING ZONE MELTING

The partial vertical sections of Y–Ba–Cu–O phase diagram have been studied. The results show that Y1Ba2Cu3O7−x (123) phase melts incongruently around 1010oC with a peritectic reaction and melting in growing single or in a great difficulty in growing single or directed crystal of 123 phase from melt by using normal solidification technologies. The new laser floating zone melting technique has been applied for manufacturing crystal rod of YBaCuO compound with diameter near 1.5 mm. The grown crystal can be changed into superconductor of single 123 phase with Tc above 90 K and with certain texture feature following suitable heat treatments. It is also found that oriented crystal of 123 phase can be obtained directly from YBa2Cu12Oy composition below 1010°C via eutectic reaction, and they may form composed superconductor wire with Tc near 85 K after suitable heat treatment.

PREPARATION OF BI-SR-CA-CU-O SUPERCONDUCTORS BY LASER FLOATING ZONE-MELTING TECHNIQUE

Abstract The growth of crystal fibers of BiSrCaCuO superconductors with different nominal compositions by the laser floating zone melting technique has been studied. The seeding and feeding rods for the process were prepared by common solid-state sintering. The crystals were grown with pulling rates and temperatures of the molten zones in the ranges of 0.17–10 mm/min and 900–950°C, respectively. The as-grown crystals were 0.5–1.5 mm in diameter and show high densities and aligned structures with the a-b planes parallel to the growth axis, which would be greatly helpful in reducing the weak links between grain boundaries and thus enhance transport critical current density. It was found that after a suitable post-heat-treatment (e.g. 860°C/10 h + furnace cooling), the samples with nominal composition BiSrCaCu 2 O y , gave a superconducting transition temperature of 85 K ( T c , zero ) and a rather high transport critical current density of 1800 A/cm 2 at 77 K and zero field. These samples were also characterized by X-ray diffraction, optical and scanning electron microscopies and electron probe.

STUDY ON MICROSTRUCTURES OF Bi(Pb)-Sr-Ca-Cu-O SUPERCONDUCTING WHISKERS

The Bi(Pb)-Sr-Ca-Cu-O superconducting whisker has a composition of (BiPb)2 × (SrCa)3Cu2Oy and a layered single crystal structure in which the stacked layers with the same orientation have different widths. The longitudinal direction of the whiskers is along the a- or b-axis of the (BiPb)2(SrCa)3Cu2Oy crystal. Crystal defects in the whiskers are mainly dislocations with Burgers vector of [010] or [001] and dislocation network. Some dislocation pairs with Burgers vector of [010] were observed in the bent whiskers.