Browsing by Author "KOO, HS"

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CHARACTERISTICS OF THE HIGH-TC SUPERCONDUCTING BI-PB-SR-CA-CU OXIDES DERIVED FROM AN ETHYLENEDIAMINETETRAACETIC ACID PRECURSOR
(1992-01-01)
CHEN, FH
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KOO, HS
;
TSENG, TY
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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+].
EFFECT OF AG2O ADDITIVE ON MICROSTRUCTURE AND SUPERCONDUCTIVITY OF THE TL2BA2CA2CU3OY COMPOUND
(1993-06-21)
KOO, HS
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HURNG, WM
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LEE, WH
;
TSENG, TY
;
CHEN, M
A series of Ag-doped Tl2Ba2Ca2Cu3Oy superconducting Oxides were prepared by a solid-state reaction and the influence of Ag2O content, with a varying molar ratio which ranged from 0 to 1.0, was also investigated. The normal-state resistance of the samples decreased with an increase in the content of Ag2O additive, while the critical superconducting temperatures of the Ag-doped samples increased once the Ag2O content was increased. The doping of the silver oxide was indicated from the results of the x-ray diffraction pattern to be favorable to the formation of the three CuO layers with a high-T(c) phase T12Ba2Ca2Cu3Oy. The diamagnetic Property of the samples was also confirmed by the magnetic measurements to become enhanced by doping with silver oxide. The platelike grains of Tl2 Ba2CaCu2Oy phase Were Observed from scanning electron micrographs to be primarily present in the undoped sample, while the amount of the needlelike Tl2Ba2Ca2Cu3Oy grain increased with an increase in the doping amount of Ag2O.
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.
HIGH-TC SUPERCONDUCTING OXIDE FILM PREPARED BY SPRAY PYROLYSIS COATING
(1990-11-01)
KOO, HS
;
TU, GC
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CHU, JJ
;
LEE, WH
;
WU, PT
PREPARATION AND CHARACTERIZATION OF TL-BA-CA-CU-O SUPERCONDUCTING FILMS BY SPRAY-PYROLYSIS AND TL-DIFFUSION TECHNIQUE
(1994-01-01)
KOO, HS
;
TU, GC
;
TSENG, TY
;
材料科學與工程學系
;
電子工程學系及電子研究所
The present work reports that highly c-axis-oriented Tl-Ba-Ca-Cu-O superconducting films with zero-resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl-diffusion treatment. The insulating Ba-Ca-Cu-O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300-degrees-400-degrees-C) MgO(001) single-crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the superconducting phases could be achieved more readily by using the bulk Tl-Ba-Ca-Cu-O rather than Tl2O3 as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl-vapor pressure is favorable for the formation of a higher T(c) superconducting phase. The dominant phases in the prepared films were mainly TlBa2Ca2Cu3Oy(1223 phase) and Tl2Ba2CaCu2Oy(2212 phase). The critical current density of a film with a nearly single-phase(1223) structure was measured to be 1.2 X 10(4) A/cm2 at 77 K under zero magnetic field.
PREPARATION AND PROPERTIES OF GEL-DERIVED HIGH-TC YBA2CU3O7-X SUPERCONDUCTOR
(1990-07-01)
KOO, HS
;
WU, PT
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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
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CHEN, FH
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KOO, HS
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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
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KOO, HS
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TSENG, TY
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LIU, RS
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WU, PT
SYNTHESIS AND CHARACTERIZATION OF BI-PB-SR-CA-CU-O SUPERCONDUCTOR VIA ETHYLENEDIAMINE CHELATING
(1991-01-01)
FRAN, YS
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KOO, HS
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CHEN, FH
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HUANG, CJ
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TSENG, YT
SYNTHESIS OF A 90 K Y2BA4CU7O15-X SUPERCONDUCTOR UNDER AMBIENT-PRESSURE BY TRIETHYLAMMONIUMOXALATE COPRECIPITATION
(1993-10-01)
CHEN, TM
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HO, JS
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LIU, RS
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KOO, HS
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應用化學系
A 90 K superconducting Y2Ba4Cu7O15-x (247) powder with fine and homogeneous grain size was prepared by oxalate/triethylamine co-precipitation of a stoichiometric amount of mixed cations of yttrium, barium and copper from their aqueous solution of nitrate salts. Characterization results of the 247 superconductor by X-ray diffraction, electrical resistivity and magnetization measurements are reported. The intragrain critical current density (J(c)) of the as-prepared 247 superconductor was derived from magnetic hysteresis to be 8.5 X 10(6) A/cm2 at 5 K and 1 T. This new route may have considerable potential in the large-scale preparation of Y2Ba4Cu7O15-x.
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
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KOO, HS
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TSENG, TY
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電控工程研究所
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Institute of Electrical and Control Engineering
SYNTHESIS OF HIGH-TC YBA2CU3O7-X SUPERCONDUCTORS AT A LOW ANNEALING TEMPERATURE FROM A GLASS PRECURSOR
(1989-01-01)
KOO, HS
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TSENG, TY
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LIU, RS
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HUANG, YT
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KUAN, KS