Browsing by Author "CHEN, FH"

Now showing 1 - 14 of 14

CHARACTERISTICS OF THE HIGH-TC SUPERCONDUCTING BI-PB-SR-CA-CU OXIDES DERIVED FROM AN ETHYLENEDIAMINETETRAACETIC ACID PRECURSOR
(1992-01-01)
CHEN, FH
;
KOO, HS
;
TSENG, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The modified sol-gel method using ethylenediaminetetraacetic acid as a chelating agent to prepare high-T(c) superconducting Bi-Pb-Sr-Ca-Cu oxides is reported. Results revealed that the desirable Bi-based compounds can be acquired by such a process with a high percentage of the 110 K phase and a T(c)(zero) of 108 K. On the other hand, a new method is proposed to quantitatively evaluate the volume fraction of the 110 K phase in Bi-based superconducting materials, mainly composed of 85 and 110 K phases. That is a lever-rule type of relation, V = (Y - 29.07-degrees)/(28.81-degrees - 29.07-degrees), where V is the volume fraction of the 110 K phase and Y = 2-theta for the X-ray diffraction peak emerging at about 29-degrees with a CuK-alpha radiation source and 28.81-degrees less-than-or-equal-to Y less-than-or-equal-to 29.07-degrees. The volume fraction of the 2223 phase estimated in this way is more reliable than that estimated by measuring the area ratios of XRD peaks and it is expected to be even more reliable than those derived from conventional methods based on perfect diamagnetism.
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+].
DOUBLE RESONANT BEHAVIOR OF MICROSTRIP RING-RESONATOR IN TL-BASED HIGH T-C SUPERCONDUCTING FILMS
(1994-12-19)
WU, SC
;
YEH, CY
;
CHEN, FH
;
TSENG, TY
;
WANG, C
EFFECT OF CA2PBO4 ADDITIONS ON THE FORMATION OF THE 110-K PHASE IN BI-PB-SR-CA-CU-O SUPERCONDUCTING CERAMICS
(1991-02-11)
CHEN, FH
;
KOO, HS
;
TSENG, TY
;
交大名義發表
;
電控工程研究所
The growth of the Bi2Sr2Ca2Cu3O(x) phase in the high T(c) superconducting Bi-Pb-Sr-Ca-Cu-O system through reacting Bi2Sr2CaCu2O(x) with Ca- or Cu-rich intermediate phases, Ca2CuO3, CuO, and Ca2PbO4, has been studied. X-ray diffraction and electrical and diamagnetic analyses revealed that the interaction and interdiffusion of these intermediate phase led to the formation of a high percentage of the 2223 phase and a sharp single-step superconducting transition at T(c)(R = 0) = 108 K. Also, Ca2PbO4 proved essential for accelerating the growth rate of the 110 K phase from the 85 K phase.
FORMATION OF HIGH-TC SUPERCONDUCTING BI-PB-SR-CA-CU OXIDE-FILMS BY SPRAY PYROLYSIS OF AN OXALATE SUSPENSION
(1990-04-01)
CHEN, FH
;
TSENG, TY
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
GROWTH PARAMETER EFFECT IN SUPERCONDUCTING YBA2CU4O8 THIN-FILMS BY DC MAGNETRON SPUTTERING
(1994-11-01)
WU, SC
;
HSU, HT
;
CHEN, FH
;
CHANG, WR
;
TSENG, TY
High-T-c YBa2Cu4O8 (124) thin films have been made by d.c. magnetron sputtering deposition on (100) MgO substrates. The effect of several processing variables, including the ratio of oxygen to argon, total pressure, and substrate temperature, on the superconducting properties of the thin films, were systematically investigated. The as-prepared films annealed in flowing oxygen at 800 degrees C for 4 h under ambient pressure obtained nearly phase-pure 124 and exhibited superconducting onset transition at 75 K.
INTERPRETATION OF THE ANOMALOUS FIELD-COOLED-MAGNETIZATION BEHAVIOR OF HIGH-TEMPERATURE GRANULAR SUPERCONDUCTORS AT LOW MAGNETIC-FIELD
(1993-07-01)
CHEN, FH
;
TAI, MF
;
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.
PARAMAGNETIC MEISSNER EFFECT OF HIGH-TEMPERATURE GRANULAR SUPERCONDUCTORS - INTERPRETATION BY ANISOTROPIC AND ISOTROPIC MODELS
(1995-02-01)
CHEN, FH
;
HORNG, WC
;
HSU, HT
;
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 exhibits the paramagnetic Meissner effect (PME), i.e., the diamagnetic signal initially increases with decrease in temperature but reaches a maximum at temperature T-d and later decreases with decrease in temperature. Even in some samples the signal is ultimately able to transform inversely into a paramagnetic regime once the sample is cooled below a temperature T-p as long as the applied field is sufficiently small. This PME has been observed in various high-T-c cuprates and is explained by disparate aspects. An anisotropic model, in which the granular superconductors are assumed to be ideally anisotropic, was first alternatively proposed in the present work so as to theoretically account for this effect. On the other hand, an isotropic model, suitable for granular superconductors with randomly oriented grains, was proposed to deal with the samples prepared by a conventional solid-state reaction method. The anomalous magnetization behavior in the present model was demonstrated to be the superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, over the paramagnetic one due to the induction of the intergranular component induced by these currents where the intergranular one behaved as the efective pinning centers. The PME was demonstrated by this model to exist parasitically in granular superconductors. This intergranular effect is therefore worthy of remark when evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.
PREPARATION AND PROPERTIES OF GEL-DERIVED HIGH-TC YBA2CU3O7-X SUPERCONDUCTOR
(1990-07-01)
KOO, HS
;
WU, PT
;
CHEN, FH
;
TSENG, TY
;
電控工程研究所
PREPARATION OF HIGH-TC SUPERCONDUCTING BI-PB-SR-CA-CU-O CERAMICS BY THE METHOD OF THERMAL-DECOMPOSITION OF AN ETHYLENE DIAMINE TETRAACETATE COLLOIDAL SUSPENSION
(1990-03-01)
TU, GC
;
CHEN, FH
;
KOO, HS
;
交大名義發表
;
材料科學與工程學系
PREPARATION OF HIGH-TC SUPERCONDUCTING OXIDE IN THE BI-SR-CA-CU-O SYSTEM BY OXALATE GEL PROCESSING
(1989-07-01)
CHEN, FH
;
KOO, HS
;
TSENG, TY
;
LIU, RS
;
WU, PT
SYNTHESIS AND CHARACTERIZATION OF BI-PB-SR-CA-CU-O SUPERCONDUCTOR VIA ETHYLENEDIAMINE CHELATING
(1991-01-01)
FRAN, YS
;
KOO, HS
;
CHEN, FH
;
HUANG, CJ
;
TSENG, YT
SYNTHESIS OF HIGH-TC SUPERCONDUCTING BI-PBSR-CA-CU-O CERAMICS PREPARED BY AN ULTRASTRUCTURE PROCESSING VIA THE OXALATE ROUTE
(1990-07-01)
CHEN, FH
;
KOO, HS
;
TSENG, TY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
ZERO RESISTANCE AT 125-K IN BI(PB)-SR-CA-CU-O SUPERCONDUCTOR
(1989-11-01)
HAUNG, CJ
;
TSENG, TY
;
HEH, TS
;
CHEN, FH
;
JONG, WS