Browsing by Author "CHEN, TM"

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AM3(P2O7)2 (A = ALKALINE-EARTH METALS - M = FE, CO, NI) - DIPHOSPHATES CONTAINING INFINITE CHAINS OF EDGE-SHARING MO6 OCTAHEDRA
(1993-09-29)
LII, KH
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SHIH, PF
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CHEN, TM
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應用化學系
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Department of Applied Chemistry
Diphosphates of the stoichiometry AM3(P2O7)2 (A = alkaline-earth metals; M = Fe, Co, Ni) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Crystal data: CaNi3(P2O7)2, monoclinic, P2(1)/c, a = 7.330(3) angstrom, b = 7.589(3) angstrom, c = 9.400(3) angstrom, beta = 11 1.90(3)-degrees, V = 485.1(3) angstrom3, Z = 2, and R = 0.026; CaCo3(P2O7)2, as above except a = 7.394(l) angstrom, b = 7.6266(9) angstrom, c = 9.444(2) angstrom, beta = 11 1.73(2)-degrees, V = 494.7(l) angstrom3, and R = 0.035; SrFe3(P2O7)2, as above except a = 7.553(l) angstrom, b = 7.7477(8) angstrom, c = 9.5796(8) angstrom, beta = 112.11(1)-degrees, V = 519.4(l) angstrom3, and R = 0.029. The three compounds are isostructural, consisting of zigzag infinite chains of MO6 octahedra sharing either trans or skew edges. The infinite chains arc connected by P2O7 groups to form a three-dimensional architecture with channels parallel to the b axis. Alkaline-earth metals are located in sites within the channels. The following isostructural compounds have also been prepared: AM3(P2O7)2 (A = Sr, Ba; M = Ni, Co) and BaFe3(P2O7)2. A magnetic susceptibility study on SrFe3(P2O7)2 indicates that the material is paramagnetic with an effective magnetic moment of 5.07 mu(B) per Fe between 300 and 26 K. Below this temperature the magnetic susceptibility increases sharply to a maximum at 6 K and then decreases rapidly. Mossbauer spectra also confirm the presence of Fe(II).
AMBIENT-PRESSURE SYNTHESIS OF SUPERCONDUCTING YBA2CU4O8
(1993-12-01)
LIN, LF
;
CHEN, TM
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
A highly homogeneous and monophasic high-T(c) superconductor YBa2Cu4O8 with T(c(zero)) of 75 K and fine grain size has been synthesized at 1 atm of oxygen via a route employing polymeric ethylene glycol/citric acid (EG/CA) precursors. In addition to the chemistry involved in the preparation, the effect of preparation temperature, time of processing and EG/CA ratio in the precursor on the formation and superconductivity of the 124 phase was systematically investigated. The results of X-ray diffraction, the temperature dependence of resistivity and dc magnetic susceptibility, and the SEM microstructure studies on 124 synthesized under different conditions were also summarized.
CHEMICAL SYNTHESIS AND CHARACTERIZATION OF SUPERCONDUCTING YBA2CU4O8 AT AMBIENT-PRESSURE
(1994-12-01)
CHEN, TM
;
LIN, LF
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應用化學系
;
Department of Applied Chemistry
A monophasic high-T-c superconductor YBa2Cu4O8 with T-c(onset) 80 K and fme grain size has beeen synthesized under oxygen at 1 bar employing metal-ethandiol/citric acid (EG/CA) polyester complex precursors. In addition to the preparation, we report the results of infrared (IR) spectra, thermogravimetric analysis (TGA), and X-ray diffraction (XRD) relevant to preparation of the YBa2Cu4O8 superconductor. The effect of temperature of preparation and precursor compositions (i.e. EG/CA molar ratio) on the purity and superconductivity of the YBa2Cu4O8 compound was investigated. The temperature dependence of resistivity and normal-state resistivity of the samples varied systematically with the EG/CA ratio in the precursors. T-c(onset) and the width of the superconducting transition for YBa2Cu4O8 samples were determined to be 80 K for all samples and 6 - 9 K, respectively; the latter depended on the corresponding EG/CA ratios in the precursors. The Meissner fraction of YBa2Cu4O8 samples determined from dc magnetization tests was independent of the EG/CA ratio. Polyester precursors can potentially be applied in large-scale preparation of high T-c ceramic-oxide superconductors and superconducting thin firms.
EFFECT OF SN ON THE SUPERCONDUCTIVITY OF THE DYBA2CU3O7-DELTA SYSTEM
(1989-12-01)
WANG, C
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CHEN, LT
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CHANG, HL
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CHU, ML
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HSU, FW
ELECTRICAL TRANSPORT AND SUPERCONDUCTIVITY IN THE AU-BI2SR1.8CA1.2CU2OY COMPOSITE SYSTEM
(1992-02-15)
LIN, WY
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LIN, JJ
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CHEN, TM
;
應用化學系
;
Department of Applied Chemistry
We have measured the resistivity-rho of the Au-Bi2Sr1.8Ca1.2Cu2Oy composite system with Au volume fraction p(Au) ranging from 0.00 to 1.00. We find, for the samples with p(Au) less-than-or-equal-to 0.4, that the addition of Au does not disturb the superconducting transition temperature of Bi2Sr1.8Ca1.2Cu2Oy. For the samples with p(Au) greater-than-or-equal-to 0.6, no zero-resistivity state is observed. The variation of rho(300 K) with p(Au) indicates a three-dimensional percolating Au matrix occurring at p(Au) almost-equal-to 0.18.
ELECTRICAL TRANSPORT IN THE AG-BI2SR1.8CA1.2CU2OY COMPOSITE SYSTEM
(1991-07-15)
LIN, JJ
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CHEN, TM
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應用化學系
;
Department of Applied Chemistry
We have measured the resistivity of the Ag-Bi2Sr1.8Ca1.2Cu2O(y) composite system with Ag volume fraction p(Ag) ranging from 0.00 to 1.00. We find, for the samples with p(Ag) < 0.6, that the addition of Ag slightly decreases the superconducting transition temperature of Bi2Sr1.8Ca1.2Cu2O(y). For the samples with p(Ag) > 0.6, no zero-resistivity state is observed. The variation of the room-temperature resistivity with p(Ag) indicates a three-dimensional percolating Ag matrix occurring at p(Ag) almost-equal-to 0.17.
FORMATION AND CHARACTERIZATION OF A SUPERCONDUCTING POLYMER COMPOSITE
(1992-04-01)
CHEN, TM
;
HU, YH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
A series of ceramic superconductor/polymer composites showing good magnetic levitation and mechanical flexibility have been prepared by dispersing Bi2-xPbxSr2Ca2Cu3Oy powder in an acrylonitrile-butadiene-styrene (ABS) rubber matrix, followed by hot or cold pressing and curing. Typically, the resistivities of the as-prepared flexible superconducting (in a magnetic sense) tapes or discs of the composite do not reach zero; however, the magnetic flux exclusion is maintained in the temperature range T < T(c) (105 K). The composites showed a large diamagnetic susceptibility that increased with increasing volume fraction of superconductor filler as indicated by magnetization measurements. The electrical and magnetic properties and microstructure of these composites are presented and their implications for future work are discussed.
HYDROTHERMAL SYNTHESIS AND CRYSTAL-STRUCTURES OF BA2FE3H(PO4)2(P2O7)2 AND BA2V3H(PO4)2(P2O7)2
(1993-10-01)
DVONCOVA, E
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LII, KH
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LI, CH
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CHEN, TM
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應用化學系
MICROSTRUCTURE, THERMOELECTRIC-POWER AND MAGNETIC IRREVERSIBILITY OF COPRECIPITATED YBA2CU4O8 POWDERS
(1992-03-01)
LIU, RS
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ZHENG, DN
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OBERTELLI, SD
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HO, JS
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CHEN, TM
The details of microstructure of triethylammonium oxalate coprecipitated YBa2Cu4O8 powders (T(c) = 83 K), prepared under one atmosphere of oxygen, were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and selected area electron diffraction (SAED). The coprecipitated powders are characterized by a submicron particle size and homogenous chemical composition of Y 1.0(3)Ba2.0(1)Cu4O8 as determined by SEM and EDS, respectively. The electron diffraction spots along the c* direction of the coprecipitated YBa2Cu4O8 microcrystals have extended streaks corresponding to a defect stacking fault. The YBa2Cu4O8 material, as prepared, is under-doped as compared to (Y0.9Ca0.1)Ba2Cu4O8 (T(c) = 88 K) as evidenced by thermoelectric power measurements. The observed magnetic irreversibility line for YBa2Cu4O8 shifts to lower temperatures as compared to that for YBa2Cu3O7; this may arise from the reduced structure dimensionality of YBa2Cu4O8 as compared to that of YBa2Cu3O7. The upper critical field [H(c)2(0)] and the Ginzburg-Landau coherence length (zeta) of the YBa2Cu4O8 material are determined to be 117 T and 17 angstrom, respectively.
PERCOLATION AND ELECTRICAL-RESISTIVITY IN THE YBA2CU3O7-AG COMPOSITE SYSTEM
(1990)
LIN, JJ
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CHEN, TM
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應用化學系
;
Department of Applied Chemistry
PERCOLATION BEHAVIOR IN A YBA2CU3O7-AG COMPOSITE SYSTEM
(1990-08-01)
LIN, JJ
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CHEN, TM
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應用化學系
;
Department of Applied Chemistry
POLYMERIC PRECURSOR DERIVED HIGH-TC BISMUTH SUPERCONDUCTORS
(1991-12-01)
CHEN, TM
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HU, YH
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交大名義發表
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應用化學系
;
National Chiao Tung University
Two bismuth-based high-T(c) oxide superconductors have been prepared by employing the polymeric citric acid/ethylene glycol (CA/EG) precursors, The polymeric precursors of mixed cations can be converted into X-ray pure Bi2Sr2CaCu2Ox (2212) and Bi1.5Pb0.5Sr2Ca2Cu3Oy (2223) phases with T(c)(zero)s in the range of 76 K and 100-110 K, respectively, and with good stoichiometry control and sample homogeneity. We describe the chemistry involved in the materials processing leading to the formation of bismuth-based superconductors and report the results from materials characterization by differential thermal analysis, resistivity and magnetization measurements.
POLYMERIC PRECURSORS FOR THE PREPARATION OF BI1.5PB0.5SR2CA2CU3OX
(1992-03-01)
CHEN, TM
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HU, YH
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交大名義發表
;
應用化學系
;
National Chiao Tung University
PREPARATION AND CHARACTERIZATION OF A CERAMIC SUPERCONDUCTOR NYLON 6,6 COMPOSITE
(1993-12-01)
LEE, SL
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CHEN, TM
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交大名義發表
;
應用化學系
;
National Chiao Tung University
To investigate a possible modification of mechanical strength of conventional ceramic superconductors for magnetic levitation and shielding applications, we have fabricated a series flexible composites with high T(c) (Bi,Pb)2Sr2Ca2Cu3Ox (2223) as a filler and a low-melting thermoplastic polymer, Nylon 6,6 as a structural matrix. These composites exhibited magnetic levitation and showed large diamagnetic flux expulsion in the temperature range of 95-110 K, although zero-resistive transition was absent even in the composites with low polymer contents. Fracture SEM studies indicated a systematic variation in the microstructure in terms of the amount of pores present and the extent of the intergrain contacts of the 2223 filler.
PREPARATION AND CHARACTERIZATION OF SOME SUPERCONDUCTOR POLYMER COMPOSITES
(1991-12-01)
CHEN, TM
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HU, YH
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交大名義發表
;
應用化學系
;
National Chiao Tung University
A technique for preparing flexible composites by dispersing high-T(c) bismuth-based superconductor filler in an ABS rubber matrix with transition temperature above 100K (based on magnetization measurements) has been developed. Superconducting tapes or discs of the Bi1.5Pb0.5Sr2Ca2Cu3Ox/ABS composites with flexibility was formed by wet or dry blending. Data obtained from dc resistivity and magnetization measurements on the composites and the features of microstructure are presented.
SOLVENT-MEDIATED IODINE INTERCALATION OF A HIGH-TC OXIDE SUPERCONDUCTOR BI2SR1.8CA1.2CU2OX
(1993-04-01)
GUO, TN
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CHEN, TM
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交大名義發表
;
應用化學系
;
National Chiao Tung University
The benzene-mediated iodine intercalation into the pseudo-layered superconductor Bi2Sr1.8Ca1.2Cu2Ox (2212) is an efficient way to prepare an intercalate with nominal composition IBi2Sr1.8Ca1.2Cu2Ox. Expansion by 22 percent along the crystallographic c-axis was observed but both a-and b-axes of the intercalates remained unchanged. The superconducting temperature (T(c)) of 2212 phase decreased 10 K upon iodine intercalation. We report the first solvent-mediated intercalation reaction and preliminary characterizations of a presumably stage-1 phase IBi2Sr1.8Ca1.2Cu2Ox.
STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF (Y,PR)(2)BA4CU7O15-DELTA PREPARED BY USING HIGH-PRESSURE TECHNIQUES
(1994-12-01)
TARNTAIR, FG
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CHEN, TM
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交大名義發表
;
應用化學系
;
National Chiao Tung University
The stability of phases in the (Y1-xPrx)(2)Ba4Cu7O15-delta (Pr-doped 247) system with x = 0 to 1.0 was investigated. The samples in the Pr-doped 247 series were prepared at 990 degrees C under 20-24 bar of oxygen atmosphere, followed by long time annealing at 300 degrees C under 120 bar of oxygen pressure. Nearly single-phase samples were obtained only for x less than or equal to 0.6-0.7 based on X-ray diffraction data. The lattice parameters of the Pr-doped 247 samples increased monotonically with increasing x due to the larger size of Pr. The superconducting transition temperature (T-c) of Pr-doped 247 samples determined from resistive measurements and field-cooled magnetization was found to be in good agreement and decreased from 88 (x = 0) to 21K (x = 0.6) with increasing x.
STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF YBA2(CU1-XAGX)3O7 WITH X-LESS-THAN-OR-EQUAL-TO-0.20
(1990-12-01)
LIN, JJ
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CHEN, TM
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CHEN, YF
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應用化學系
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Department of Applied Chemistry
SUPERCONDUCTING PROPERTY AND STRUCTURE STUDIES OF YBA2CU3O7-AG2O COMPOSITES
(1990-03-01)
LIN, JJ
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CHEN, TM
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YAO, YD
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CHEN, JW
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GOU, YS
SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF SODIUM VANADYL(IV) ORTHOPHOSPHATE NAVOPO4
(1991)
LII, KH
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LI, CH
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CHEN, TM
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WANG, SL
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應用化學系
A new sodium vanadyl(IV) orthophosphate NaVOPO4 has been synthesized by solid-state and hydrothermal method and characterized by single-crystal X-ray diffraction and magnetic susceptibility. It crystallizes in the monoclinic space group P2(1)/c with a = 6.524(1), b = 8.455(4), c = 7.119(1), beta = 115.29(1)-degrees, Z = 4, R = 0.027, and is structurally similar to the triclinic analog LiVOPO4. The structure can be described as close-packed infinite chains of trans-corner-sharing VO6 octahedra with the holes around each chain filled with Na and P atoms. These infinite chains have alternating short and long V - O bonds and are similar to those found in beta-VOPO4. The Na atom has six close oxygen neighbors at distances of 2.268 to 2.511 angstrom.