Guan Weiyan

Growth of superconducting single crystals of composition Bi:Sr:Ca:Cu=2:2:1:2 in the Bi-Sr-Ca-Cu-O system

Abstract The thermal analysis of more than ten different starting composition materials in the Bi-Sr-Ca-Cu-O system has been studied, and all these starting compositions crystallize between 800 and 800°C. Experiments show that only some of them can produce superconducting single crystals, and also suggest that the “2212” (BiSrCaCu) is the best starting composition for growing large 110 K (onset) superconducting single crystals. The largest crystals are 12×5×1 mm 3 with T c ( R =0)=83 K . The composition of the 110 K superconducting single crystal is Bi 3.3 Sr 2.6 Ca 1.1 Cu 3.0 O y .

Study of high-Tc superconducting YBaCuO thin films

Abstract The YBaCuO thin films are deposited onto several kinds of substrates by electron beam evaporation in an ultrahigh vacuum system. The nominal thickness is 1μm. After the heat treatment at 850–890°C for 1hr, the YBaCuO films on the BaF2 substrates show superconducting behaviors with the midpoint about 87K and zero resistance temperature around 77K. The room temperature resistivity of these films is about 2mΩcm. The composition and structure analysis for these films have been studied by AES, XRFS and x-ray diffraction.

A new superconducting oxide GdBaCuO with Tc (ρ=0) above 92K

Abstract A new superconducting oxide GdxBa1−xCuO3−y with Tc (ρ=0) above 92K has been successfully synthesized by the ceramic technology. The samples with composition of x=0.5, 0.625 and 0.9 are all observed with high Tc superconductivity. The highest Tc for samples measured is observed in Gd0.5Ba0.5CuO3−y which has a resistive midpoint of 95K with a width of 1.5K, and a zero-resistance temperature of 92.5K. The results of a.c. magnetic susceptibility measurement are also reported.

ION-BEAM MIXING - A NEW METHOD IN THE STUDY OF METASTABLE SUPERCONDUCTORS

Abstract A newly developed ion beam mixing technique was applied to the study of the superconductivity of AlSi alloys. The highest superconducting transition temperature T c is 7.53 K for Al-40 vol. % Si. The dose dependences of T c , Δ T c and R 0 reflect the mixing process and suggest that disorder might be the reason for T c enhancement.

Resistivity anomaly in the high-temperature superconductor Bi-Sr-Ca-Cu-O

An anomalous resistance drop was observed near 190K in the R-T measurement on a sample in Bi-Sr-Ca-Cu-O system and the transition completed at 80K. After keeping the sample at room temperature for 10h, the temperature dependence of the resistance changed from semiconducting to metallic behavior, while the ending of the transition remained at 80K. This might be an evidence of the existence of a metastable superconducting phase in Bi-Sr-Ca-Cu-O system with Tc as high as 190K.

Superconductivity of AlSi alloys formed by ion beam mixing at liquid helium temperature

Abstract Ion beam mixing of multilayered Al/Si films at low temperature ( T c and residual resistance R 0 were measured in situ after a succession of Ar ion bombardments at varying doses. The results showed that the samples within different ranges of Si concentration had different types of dose-dependence. At high doses, both R 0 and T c reached saturation. The normalized saturated resistance variation ΔR 0 / R 0 increased with increasing Si concentration, whereas the saturated T c rose to about 6.5–7.5 K for all samples within 16–40 vol% Si. After warming up to room temperature, T c decreased to about 3 K. It is proposed that the T c enhancement in AlSi alloys can be attributed mainly to the disorder induced by low temperature ion bombardment and stabilized by the Si atoms.

EPR of BiSrCaCu2Oy high Tc superconductor

Abstract The EPR of the nominal BiSrCaCu 2 O y high T c superconductor at different temperatures is investigated. It is found that there are two EPR signals with different behaviors in this sample. One of them shifts gradually toward higher magnetic field and its Lande factor g -value is decreased from 2.78 to 2.24 when the temperature is raised from 115 K to 310 K. The resonance magnetic field of another signal is almost independent of temperature and its g -value is close to one of free electron. There is only zero field signal below T c for this sample and its intensity is increased with decreasing temperature. We propose a possible interpretation for these phenomena based on electron transfer between copper ion and oxygen ion in CuO plane.

Superconducting and transport properties and the mixing process in Al/Si multilayer films

Abstract The superconducting and transport properties were studied to probe the mixing process in Al/Si multilayer films during Ar ion bombardment at liquid helium temperature. From the dose-dependences of the superconducting transition temperature Tc and the electrical resistance R0, an effective diffusion constant D ∗ was evaluated. A good agreement between this D ∗ with the value ballistic mixing theory suggests that, at low temperatures where diffusion is hardly activated the ballistic effect predominates the mixing process for the Al/Si system, where the heat of mixing has a small negative value.

Ion implantation and low temperature properties of metal-semiconductor alloys

Abstract We review the experimental work on ion implantation with respect to superconductivity and electrical resistivity of metal-semiconductor alloys carried out at the Institute of Physics of Academia Sinica. Samples studied included liquid-quenched AlSiGe ribbons and Al thin films. The liquid-quenched ribbons with a superconducting transition temperature T c of 3.2 K were implanted with H or H 2 ions at room temperature and a decrease of T c was observed. The ribbons were also implanted with Si ions at liquid nitrogen temperature, resulting in a higher onset of transition at about 4 K. We also implanted Si ions into Al thin films at room temperature up to 5 at.% Si. The T c of the films increased from 1.5 to 1.9 K and the temperature-dependence of resistivity was changed from T 5 to a T 3 -dependence within 30–50 K. The superconductivity of Al-semiconductor alloys was proved to be strongly influenced by the disorder, which depends crucially on the implantation temperature.

Effect of ion beam mixing/implantation at low temperature on superconductivity in palladium-hydrogen and palladium-copper-hydrogen systems

The highest superconducting transition temperature of 8.42 and 5.16K has been observed in the alloy system PdH and PdCuH, where the atomic ratio n=H/Pd(Cu) are 1 and 0.6, respectively. The effect of lattice disorder induced by 220 keV Ar ion beam bombardment at liquid helium-temperature is detrimental to the superconductivity.