Browsing by Author "YANG, TJ"

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A SALT SPRAY TEST ON INTERLAYER-MODIFIED TIN COATING
(1992-06-15)
CHEN, YI
;
DUH, JG
;
CHIOU, BS
;
YANG, TJ
;
電控工程研究所
ANALYSIS OF TRANSPORT CRITICAL-CURRENT DENSITY IN A BENT BI-PB-SR-CA-CU-O SILVER-SHEATHED TAPE
(1995-06-01)
LEE, WD
;
HORNG, L
;
YANG, TJ
;
CHIOU, BS
;
電子物理學系
The experimental results on the magnetic behavior of the transport critical current density in a bent Bi based superconducting tape have shown that the irreversible strain limit epsilon(irrev) for the onset of permanent strain damage to Ag sheathed superconductors is not dependent on the magnetic field, nor does the normalized I-c(H, epsilon)/I-c(0, epsilon) current depend on the strain at least up to 0.5 T at 77 K. Such a behavior has been attributed to two reasons: (1) The intrinsic pinning properties are unchanged in a bent tape; (2) The strain effect is extrinsic and arises from superconductor cracks. Thus, based on these arguments a Josephson junction tunneling model with cracks in between the grain boundaries is proposed to explain the J(c) behavior quite well for a bent granular high-T-c superconducting tape. Our model calculation shows that the critical current density of high-T-c superconductor may be enhanced by increasing the strain tolerance epsilon(irrev) and the epsilon(irrev) is determined by the properties of Ag sheathed tape and its related material parameters, which are dependent on the connectivity of the grain boundaries.
ANOMALOUS HALL-EFFECT FROM VORTEX MOTION IN HIGH-TC SUPERCONDUCTORS
(1994-08-01)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程研究所
;
Department of Electrophysics
In this work, the unusual Seebeck effect is taken into consideration in explaining the possible origin of the anomalous Hall effect for high-T(c) superconductors. Combining Maki's theory of transport entropy and Tinkham's theory of resistive transition, we explain why the anomalous Hall effect can be observed in high-T(c) superconductors, but is absent in most conventional superconductors. The behavior of rho(xy) (H, T) in our theory is qualitatively consistent with experiments. In addition, our theory not only predicts that rho(xy) will become positive from rho(xy) < 0 when the temperature is decreased in constant magnetic field, but also predicts that \rho(xy)\ is-proportional-to rho(xx)2 in the region of pho(xy) < 0 and that the negative p(xy) will diminish with increasing defect concentration.
CORRELATION BETWEEN THE SUPERCONDUCTING TRANSITION-TEMPERATURE AND MADELUNG SITE POTENTIAL DIFFERENCE IN YBA2CU3OX
(1994-02-01)
YANG, TJ
;
HORNG, L
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
The Madelung site potentials have been calculated in YBa2Cu3Ox system in order to find the role of the difference in the Madelung site potentials DELTAV(T) and DELTAV(M) within the ionic model. The bond valence sum of each of the ions in the YBa2Cu3Ox compound is assigned as charge of the corresponding ion in the calculation of the Madelung site potential. Correlations between DELTAV = 0.75 DELTAV(M) +0.25 DELTAV(T) obtained and superconducting transition temperature T(c) are examined and found qualitatively very good agreement with the well-know experimental result for the various oxygen content x. This also supports that the usual believing DELTAV(M) is of primary important parameter to control T(c). The reason will be argrued in this paper.
EFFECT OF SN ON THE SUPERCONDUCTIVITY OF THE DYBA2CU3O7-DELTA SYSTEM
(1989-12-01)
WANG, C
;
CHEN, LT
;
CHANG, HL
;
CHU, ML
;
HSU, FW
ENHANCEMENT OF MAGNETIC-FIELDS GENERATED BY HIGH-T(C) SUPERCONDUCTING COILS
(1993-12-01)
CHEN, K
;
HORNG, L
;
TAI, CH
;
WEI, JC
;
YANG, TJ
High-T(c) superconducting pancake coils wound by Ag-sheathed Bi-based tapes have been placed in between ring-shaped mu metal sheets. The central magnetic field B0 of a single coil was found to be enhanced by 60 % at liquid nitrogen temperature 77 K, and increased approximately 26 % for a four-coil stacked magnet. Critical currents of these coils were decreased. B0 was also increased when the magnet was wrapt by a mu metal sheet. This indicates that the well-designed high permeability materials can significantly enhance the magnetic fields generated by high-T(c) superconducting magnets.
FLUX-FLOW OF ABRIKOSOV VORTICES IN TYPE-II SUPERCONDUCTORS
(1994-07-01)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程研究所
;
Department of Electrophysics
The theory of flux flow developed by Bardeen and Stephen (BS) is modified and extended to the high-field case. The Clem model and Wigner-Seitz circle-cell approximation for vortices are used in our approach. The distinct boundary of the normal core of a vortex in BS theory is removed and treated naturally. Several interesting results come out as a consequence. The Lorentz force is determined by the normal current rather than the supercurrent. But the supercurrent can sustain the magnetic-field distribution of flux quanta. From energy dissipation considerations, the Lorentz force is equal to viscosity force automatically without assumption as made in BS theory. An expression for the viscosity is also obtained.
HYSTERETIC BEHAVIOR OF THE TRANSPORT CRITICAL-CURRENT DENSITY IN A BENT BI-PB-SR-CA-CU-O SILVER-SHEATHED TAPE
(1995-04-15)
LEE, WD
;
HORNG, L
;
YANG, TJ
;
CHIOU, BS
;
電子物理學系
MAGNETIC-RELAXATION IN A AG-SHEATHED HIGH-JC BI-PB-SR-CA-CU-O SUPERCONDUCTING TAPE
(1991-12-01)
CHEN, K
;
LEE, WH
;
HORNG, L
;
YANG, TJ
;
電子物理學系
The magnetic relaxation and magnetization curves were studied on the Ag-sheathed and highly c-axis oriented Bi-Pb-Sr-Ca-Cu-O tape with transport J(c) > 10(4) A/cm2 at 77 K. Zero-field-cooled (ZFC) in-field relaxation for applied field perpendicular to the sample a-b plane was investigated. It was found that the field-dependent relaxation rate had a maximum in the certain applied field at various temperatures. The applied field at this maximum was greater than H*, the first field for which currents flow through the entire volume of the sample in the Bean's critical state model. Pinning energies were estimated at the maximal relaxation rate in a series of temperatures.
MECHANICAL-PROPERTIES OF AG-SHEATHED BI-BASED SUPERCONDUCTING TAPES
(1993-12-01)
HORNG, L
;
CHEN, K
;
LEE, WD
;
WEI, JC
;
YANG, TJ
Flexible Ag-sheathed Bi-based superconducting tapes have fabricated by powder-in-tube technique. The critical current density (J(c)) does not varied when the bending radius is larger than the critical bending radius R0, bending radius without deteriorating transport properties. The bending tests were studied under magnetic field up to 5,000 G. The critical bending radius R0 (or Critical bending strain epsilon(b0)) was found to be independent of magnetic field from 0 to 5,000 G. The J(c)(B)/J(c)(0) curves are super-imposed in the same curve, i.e., the transport behavior of a tape at magnetic field is not affected by bending. It implies that the intrinsic pinning properties of a bent tape are unchanged in magnetic field. The results are useful for making a react-and-wind magnets and cables.
NONLOGARITHMIC MAGNETIC-RELAXATION IN A HIGHLY ORIENTED BI-BASED SUPERCONDUCTING TAPE
(1993-12-01)
WEI, JC
;
HORNG, L
;
YANG, TJ
;
CHEN, K
;
電子物理學系
Magnetic Relexation was studied at a wide range of temperatures and magnetic fields for a Ag-sheathed Bi-based superconducting tape with highly-c-axis orientation and high critical current density (J(c) > 10(4) A/cm2 at 77 K and 0 T). Under certain conditions, it is found that the magnetization data varies nonlinearly with ln(t) for entire period of time (t > 10(4) s). The curves can be divided into two relaxation rate (dM/dln(t)) in different period of time. It was observed that the lower the temperature is, the higher the magnetic field needs to bend a logarithmic line into a curve with two different relaxation rate (dM/dln(t)) in different region of time. The diagram of temperature and magnetic field was obtained from the experiment.
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-09-20)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with xi(0)>>k(F)(-1) may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter psi(x) is not depleted but enhanced near the surface. We also obtain some interesting results: T-c will be enhanced by contracting of the thickness of a superconducting film. The nucleation field H-c3(T) proportional to (T-cb-T) near T-cb; and H-c3(T)proportional to(T-c-T)(1/2) near T-c. The critical current in SIS Josephson junctions J(c)(T)proportional to(T-c- T) + root 2 tau(0)(T-0-T) for T
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-09-20)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程研究所
;
Department of Electrophysics
Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with xi(0)>>k(F)(-1) may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter psi(x) is not depleted but enhanced near the surface. We also obtain some interesting results: T-c will be enhanced by contracting of the thickness of a superconducting film. The nucleation field H-c3(T) proportional to (T-cb-T) near T-cb; and H-c3(T)proportional to(T-c-T)(1/2) near T-c. The critical current in SIS Josephson junctions J(c)(T)proportional to(T-c- T) + root 2 tau(0)(T-0-T) for T
THE HYSTERESIS OF MAGNETIZATION IN THE GENERALIZED CRITICAL-STATE MODEL - LOW-FIELD APPROXIMATION
(1994-05-01)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
The generalized critical-state model is extended to the low-field case by a new low-field approximation. We calculate the hysteresis loops of magnetization for H(max) < H* and H(max) > H*. We obtain new behaviors of M(H) which are different from the results derived from the Bean and Kim models. Our theory qualitatively agrees with the experimental results for high-T(c) superconductors. Some important macroscopic parameters may be obtained by fitting our theory with the experimental data.