Browsing by Author "HORNG, L"

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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.
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.
CORRELATIONS AMONG C/B, TC, AND MADELUNG POTENTIALS IN THE SYSTEM OF RBA2CU3OX SUPERCONDUCTORS
(1989-11-01)
TSAY, SF
;
WANG, SY
;
HORNG, L
;
YANG, TJW
;
電子物理學系
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.
HIGH ORIENTATION CDS THIN-FILMS GROWN BY PULSED LASER AND THERMAL EVAPORATION
(1992-05-01)
DAI, CM
;
HORNG, L
;
HSIEH, WF
;
SHIH, YT
;
TSAI, CT
Undoped CdS films have been grown by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques on Corning's 7059 glass at a substrate temperature between room temperature and 250-degrees-C. The deposition rates are 0.07 angstrom/s for PLE and 60 angstrom/s for the TE technique. These as-deposited films have high (002) preferred orientation by both techniques even without preheating the substrate. However, films deposited by PLE have more preferred orientation and larger grain size. These features make the PLE films have sharper Raman peaks, smaller Raman shift of surface mode and more overtones of longitudinal optical phonon mode observed than those in TE films. The transparency of PLE or TE films for wavelengths which are larger than that of absorption edge is around 90% on average.
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
LATTICE RELAX, CHARGE-TRANSFER, AND MADELUNG POTENTIAL-ENERGY IN YBCO SYSTEMS
(1993-12-01)
HORNG, L
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
We have calculated Madelung potential energies by Ewald's method in YBa2Cu3-xMxO7-delta system (M = Ni, Zn, Co, Fe, etc.). The Madelung potential energy, long-range Coulomb interaction, is expected to give a major contribution in these partially ionic copper-oxide superconductors, Concerning site preference of dopant ions, the results from the calculated Madelung energies can not only interpret the site preference of dopant ions substituting for copper sites, which are in accordance with most experimental results, but also illustrate strongly that the holes transfer from sheets to chains on substitution. The apical oxygen is a balancing bridge of charge-transfer, and leads to lattice variation of Cu-0 bond length which is due to long-range Coulomb force. These suggest that this kind of charge-transfer channel is one of important factors to affect T(C) values.
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.