Browsing by Author "SHI, JB"

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ANISOTROPIC IRREVERSIBILITY LINES FOR C-AXIS ALIGNED (BI, PB)2CA2SR2CU3O10+DELTA POWDERS
(1992-04-15)
SHI, JB
;
CHIOU, BS
;
KUO, PL
;
KU, HC
;
電控工程研究所
Anisotropic irreversibility lines due to thermal fluctuation for quasi-two-dimensional high-T(c) superconductors were observed in c-axis-aligned powders of the (Bi, Pb)2Ca2Sr2Cu3O10+deltaBi(2223) compound with T(c) = 108 K. The anisotropic ratio H(r)(perpendicular-to c)/H(r)(parallel-to c) decreases sharply from 13.6 at 100 K to low values of 3.2 at 80 K and 3.1 at 70 K. The simple 3D-like power law H(r)=a.(1 - T/T(c))n was observed only in the low field region (less-than-or-equal-to 200 G) with n=2.19 for H perpendicular-to c and 2.99 for H parallel-to c. In the higher field region up to 4 kG, the temperature dependence of H(r)(T) lines changes into a 2D-like exponential function H(r) = b.exp (-T/T0) due to the breakdown of the interlayer and/or intralayer coupling of the conduction channel which consists of three Cu-0 planes, with T0 = 14.2 K for H perpendicular-to c and 13.7 K for H parallel-to c. The magnetic susceptibility ratio chi(c)/chi(ab) for this highly anisotropic superconductor in a low applied field of 8 G increases sharply from 9.8 at 5 K to 17.9 near T(c).
ANISOTROPIC IRREVERSIBILITY LINES FOR C-AXIS ALIGNED POWDERS OF THE BI(2223) COMPOUND (BI,PB)2CA2SR2CU3O10+DELTA
(1991-12-01)
SHI, JB
;
KUO, PL
;
CHIOU, BS
;
KU, HC
;
電控工程研究所
Anisotropic irreversibility lines were observed for c-axis aligned powders of the Bi(2223) compound (Bi,Pb)2Ca2Sr2Cu3O10+delta (T(c) = 108 K). The aligned sample was prepared using powders embedded in epoxy and aligned in a 9.4 T applied magnetic field at room temperature. The anisotropic irreversibility lines H(r)(T) were measured with applied field H parallel and perpendicular to the c-axis. The simple power law H(r) = a.(1 - T/T(c))n with n = 2.19 (H perpendicular-to c) and n = 2.99 (H parallel-to c) were observed only in low applied field H less-than-or-equal-to 250 G. For applied field up to 4 kG, H(r)(T) lines were better fitted with the exponential law H(r) = b.exp(-T/t).
ANISOTROPIC MAGNETIC-PROPERTIES OF BI2SR2CUO6+DELTA SINGLE-CRYSTAL
(1992-07-01)
SHI, JB
;
CHIOU, BS
;
HO, JC
;
KU, HC
;
電控工程研究所
Single crystals of Bi2Sr2CuO6+delta were synthesized and characterized by X-ray diffraction. The Bi(2201) sample remains not superconducting or magnetically ordered down to 5 K. With an applied magnetic field perpendicular or parallel to the c-axis, magnetic measurements yielded anisotropic magnetic susceptibilities chi(c)(H perpendicular-to c) and chi(ab)(H parallel-to c). Both can be fitted to the sum of a temperature-independent chi(0) and a Curie-Weiss term C/(T + theta(p)) in the temperature range between 5 and 300 K, with a common Curie constant C = 1.0 x 10(-2) cm3 K/mol and Curie-Weiss paramagnetic intercept theta(p) = + 1.1 K. Since the resulting Curie-Weiss term is the same for both directions, the overall anisotropy DELTA(chi) = chi(c) - chi(ab) = DELTA(chi-0) is also temperature independent. Its magnitude, 3.3 x 10(-5) cm3/mol, however, is lower than the corresponding values for Bi(2212) (2.3 x 10(-4) cm3/mol) and Bi(2223) (5.8 x 10(-4) cm3/mol).
ANISOTROPIC SUPERCONDUCTING PROPERTIES OF ALIGNED (BI,PB)2CAN-1SR2CUNO2N+4+DELTA POWDERS (N = 1, 2, 3) WITH TC = 32, 94, AND 110 K
(1991-06-01)
SHI, JB
;
CHIOU, BS
;
KU, HC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The anisotropic superconducting properties of aligned powders embedded in epoxy for bismuth copper oxides with the compositions (Bi1.6Pb0.4)(Sr1.5La0.5)CuO6+delta (n = 1, T(c) = 32 K), Bi2Ca1.2Sr1.8Cu2O8+delta (n = 2, T(c) = 94 K), and (Bi1.85Pb0.15)Ca2.2Sr1.8Cu3O10+delta (n = 3, T(c) = 110 K) are reported. These c-axis-aligned samples were prepared in a 9.4-T applied magnetic field at room temperature The temperature dependence of the anisotropy ratio chi-c(T)/chi-ab(T) in the superconducting state is derived from both zero-field-cooled and field-cooled data using a small applied field H (less than or equal to the lower critical field H(c1)) parallel and perpendicular to the orthorhombic c axis. A highly anisotropic chi-c/chi-ab ratio was observed for all three systems, the maximum value of chi-c/chi-ab = 9.8 at 5 K and 10.8 at 85 K for the 2:2:2:3 compound (Bi1.85Pb0.15)Ca2.2Sr1.8Cu3O10+delta was observed. The field dependence of the anisotropy ratio chi-c(H)/chi-ab(H) for the 2:1:2:2 compound Bi2Ca1.2Sr1.8Cu2O8+delta up to 5 kG is discussed.
COBALT ORDERING IN LAYERED BI2SR2COO6+DELTA-SINGLE CRYSTAL
(1993-01-15)
SHI, JB
;
HO, JC
;
LEE, TJ
;
CHIOU, BS
;
KU, HC
Insulating Bi2Sr2CoO6+delta is nearly isomorphic with the Bi(2201)-type high-T(c) superconductors. Magnetic and calorimetric studies were carried out on single crystal samples of this layered compound. Based on magnetic measurements, the cobalt ions undergo a canted antiferromapetic ordering at T(N) = 159 K. A low-temperature neutron diffraction study of the magnetic structure is in progress. The molar magnetic susceptibility chi(ab)(H perpendicular-to c) above 200 K can be well fitted by the Curie-Weiss form chi(ab)(T) = chi0+C/(T-theta(p)), with chi0 = 0.56 cm3K/mol, Curie constant C = 3.2 x 10(-2) cm3K/mol and Curie-Weiss intercept theta(p) = 159 K. There is no magnetic specific heat peak, however, prevailing around T(N). This anomalous calorimetric behavior is attributed to the two-dimensional quantum spin fluctuation of Co spins above T(N) in the layered compound as previously observed for Cu spins in (Gd1.85Ce0.15)CuO4-delta and La2CuO4-delta.
MAGNETIC PHASE-DIAGRAM OF 32-K SUPERCONDUCTOR (BI1.6PB0.4)(SR1.5LA0.5)CUO6+DELTA
(1990-08-01)
KU, HC
;
SHI, JB
;
LAI, CC
;
SUN, SJ
;
電控工程研究所
ORIENTATION-DEPENDENT X-RAY ABSORPTION FINE-STRUCTURE (XAFS) OF THE BI-SR-CA-CU-O SYSTEM
(1992-12-01)
CHOU, CH
;
PONG, WF
;
SHI, JB
;
KU, HC
;
LIN, IN
Using the transmission and fluorescence modes at the National Synchrotron Light Source (NSLS) X-23A2 beam line, we have measured polarized XAFS spectra of the Bi, Pb L3-edges and the Cu K-edge for the (Bi1.85Pb0.15)Ca2.2Sr1.8Cu3O10+delta sample and unpolarized XAFS spectra of the Bi, Pb L3-edges and the Cu K-edge for Bi2Ca1.2Sr1.8Cu2O8+delta, Pb0.2Bi1.9Sr1.9Cu1O6+delta and (PbxBi2-x)Sr2Ca2Cu3Oy (x = 0, 0.2, 0.4) samples. All XAFS spectra were measured at room temperature. The incommensurate modulations in the Bi-O layers are discussed in terms of the XAFS technique. The XAFS spectra of Bi L3-edge do not vary substantially for different sample orientation with respect to the X-ray polarization vector E. There is evidence for the existence within the Bi-Sr-Ca-Cu-O system of Bi atoms having the oxidation number exceeding 3. Pb ions predominantly substitute for Bi ions in the Bi-Sr-Ca-Cu-O system because there is no significant difference between the XANES spectra of the Pb and Bi L3-edges, respectively. The oxidation numbers of substituted Pb in Bi-Sr-Ca-Cu-O system differ much from those of Pb in PbO2 in which the oxidation number of all Pb atoms is 4. In agreement with other investigators, our results on the polarized XANES spectra of the Cu K-edge indicate that a satellite about 7 eV above the main K-XANES peak in both polarizations is a multielectron excitation to the final-state configuration 1s3d9epsilonp1, and that a shoulder on the rising absorption edge, present for many Cu compounds and generally assigned to a shake-down multielectron excitation, is a transition to a final state of the Cu compounds. We have also deduced that the structure of the Cu-O planes in the Bi-Sr-Ca-Cu-O samples is ordered.
THE CORRELATION BETWEEN SUPERCONDUCTIVITY AND CU-O BOND LENGTH FOR THE SINGLE CU-O LAYER COMPOUNDS WITH THE BI2SR2CUO6+DELTA-TYPE (2021) STRUCTURE
(1991-12-01)
KU, HC
;
SUN, SJ
;
SHI, JB
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The structure and superconductivity in the single Cu-O layer bismuth (2021) system can be stabilized also by the doping of Na1+ ions. Contrary to the La-doped Bi2(Sr,La)2CuO6+delta system with T(c) enhancement up to 35 K. T(c) remains around 10 K for the Na-doped Bi2(Sr2-xNax)CuO6+delta system (0.0 less-than-or-equal-to x less-than-or-equal-to 0.4). The variation of T(c) with the Cu-O bond length r(Cu-0) in the Cu-O layer for the Bi family which consists of the systems (Bi,Pb)2Sr2CuO6+delta, Bi2(Sr,Na)2CuO6+delta, Bi2(Sr,La)2CuO6+delta and (Bi,Pb)2(Sr,La)2CuO6+delta indicates an optimum r(Cu-0) value of 1.906-1.913 angstrom with maximum T(c) of 35 K for these Bi(2021) compounds.
THE OCCURRENCE OF SUPERCONDUCTIVITY IN THE TLBA2CUO5-DELTA-TYPE-(1021) SYSTEM
(1989-06-01)
KU, HC
;
TAI, MF
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SHI, JB
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SHIEH, MJ
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HSU, SW