Browsing by Author "TAI, MF"

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COPPER VALENCY OF SUPERCONDUCTING PHASES IN THE PB-DOPED BI-SR-CA-CU-O SYSTEM
(1992-07-01)
CHEN, FH
;
KOO, HS
;
WU, SC
;
TSENG, TY
;
HORNG, SR
Pb-doped Bi-Sr-Ca-Cu high-T(c) superconducting oxides have been prepared by a modified sol-gel process via the EDTA route. Upon decomposing the X-ray photoemission spectrum of the Cu 2p3/2 core level of the superconducting oxide into three components Cu1+, Cu2+ and Cu3+, we have found an obvious trend: the corresponding [Cu1+]/[Cu2+] ratio increased as more 110 K phase was formed in the sample. According to this trend, a defect model was proposed; it can reasonably explain some previous experimental results, such as a reduced oxygen atmosphere sintering, which effectively facilitates the formation of the 110 K phase, and the coexistence of copper and oxygen vacancies in Bi-system superconductors, observed by high-resolution transmission electron microscopy. On the other hand, the dimerization of holes in oxygen sites was also suggested to be a possible mechanism responsible for the increase in the ratio of [Cu1+]/[Cu2+].
ENHANCED DIAMAGNETISM IN YBA2CU3O7-DELTA BY HYDROGEN-PLASMA TREATMENT
(1994-09-10)
LEE, MW
;
TAI, MF
;
LEE, HJ
;
HWANG, HL
;
KAO, HCI
We report that the diamagnetism of as-grown YBa2Cu3O7-delta powders can be enhanced by treatment with RF-generated hydrogen plasma. The field-cooling susceptibility at 5 K is found to increase by up to 24%. The enhancement is reproducible for all five samples studied. The lattice parameter c decreases after hydrogenation. For a sample treated for the shortest period, its pinning potential, obtained from magnetic relaxation measurements, is reduced following H-treatment.
INTERPRETATION OF THE ANOMALOUS FIELD-COOLED-MAGNETIZATION BEHAVIOR OF HIGH-TEMPERATURE GRANULAR SUPERCONDUCTORS AT LOW MAGNETIC-FIELD
(1993-07-01)
CHEN, FH
;
TAI, MF
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HORNG, WC
;
TSENG, TY
;
電子工程學系及電子研究所
The field-cooled magnetization of high-T(c) superconducting ceramics measured in low magnetic fields has exhibited an unusual phenomenon, i.e., the diamagnetic signal initially increases with a decrease in temperature but reaches a maximum at temperature T(d) and subsequently decreases with a decrease in temperature. In some samples the signal could even transform inversely into a paramagnetic regime once the sample was cooled below a temperature T(p), provided the applied field was sufficiently small. This phenomenon has been observed in various high-T(c) cuprates and been explained with different viewpoints. An alternative theoretical model was proposed in this work to account for these phenomena. The anomalous magnetization behavior in the present model was demonstrated to be a superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, and the paramagnetic signal, due to the induction of the intergranular component induced by these currents. The intergranular effect was demonstrated by this model to exist in granular superconductors. This intergranular effect would therefore be considered in evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.
THE OCCURRENCE OF SUPERCONDUCTIVITY IN THE TLBA2CUO5-DELTA-TYPE-(1021) SYSTEM
(1989-06-01)
KU, HC
;
TAI, MF
;
SHI, JB
;
SHIEH, MJ
;
HSU, SW