Browsing by Author "LAI, CC"

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ANOMALOUS PR ORDERING IN THE NEW TLBA2PRCU2O7-DELTA COMPOUND
(1992-11-01)
LAI, CC
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CHIOU, BS
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CHEN, YY
;
HO, JC
;
KU, HC
Magnetic measurements on the new tetragonal Tl(1212) compound TlBa2PrCu2O7-delta (a = 3.910 angstrom and c = 12.53 angstrom) reveal an anomalously high antiferromagnetic Neel temperature T(N) congruent-to 8 K. This transition temperature is higher than T(N) = 2.2 K for isostructural TlBa2GdCu2O7-delta. Corroborative evidence comes from calorimetric studies, in which a magnetic entropy was obtained DELTAS congruent-to 0.5 Rln 2 between 2 and 10 K, as well as a sizeable linear term in specific heat comparable to those found in heavy-fermion systems. Through structural consideration, these observations can not only be correlated to the almost identical but still puzzling features of PrBa2Cu3O7-y, but also remove some ambiguity in the interpretation of earlier results.
COMPARATIVE-STUDIES OF GD-ORDERING IN VARIOUS CUPRATE SYSTEMS
(1994-02-01)
HO, JC
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WU, CY
;
LAI, CC
;
SHIEH, JH
;
KU, HC
Gd-ordering near 2.2 K in both superconducting and nonsuperconducting GdBa2Cu3O7-y has been well documented. This report summarizes our results from comparative studies on other Gd-containing cuprates (with well-defined Neel temperatures in parentheses) including Bi2Sr2GdCu2O8 (1.6 K), TlBa2GdCu2O7 (2.2 K), TlSr2GdCu2O7 (2.4 K), (Pb.5Cu.5)Sr2GdCu2O7 (2.3 K), Pb2Sr2GdCu3O8 (2.3 K), Gd2CuO4 (6.6 K) and (Gd1.85Ce0.15)CuO4 (5.3 K). The Neel temperature values for the Bi-, Tl-, and Pb-based cuprates remain close to that for PrBa2Cu3O7-y having similar layered structures but somewhat different Gd-Gd distance along the c-axis, whereas the T'(214) compounds become ordered at higher temperatures. Also to be noted is the general occurrence of a broad shoulder below the heat capacity peak, which needs to be taken into account for obtaining the expected magnetic entropy DELTAS = Rln8 associated with the ordering.
MAGNETIC AND CALORIMETRIC STUDIES OF GD ORDERING IN TLBA2GDCU2O7-DELTA
(1993-05-01)
CHEN, YY
;
LAI, CC
;
CHIOU, BS
;
HO, JC
;
KU, HC
Antiferromagnetic ordering among Gd3+ ions in the nonsuperconducting compound TiBa2GdCu2O7-delta occurs near 2.2-2.3 K as confirmed by magnetic and calorimetric measurements. This compound is similar in structure to that of superconducting GdBa2Cu3O7-y, but with the Cu-O chains replaced by Tl-O planes, which also exhibits a similar magnetic transition at 2.2-2.3 K. This paper further compares the Neel temperatures and magnetic specific-heat anomalies of various Gd-containing compounds and related systems. Some common features between the compounds are discussed.
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
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電控工程研究所
MAGNETIC-BEHAVIOR IN PR-CONTAINING TL-BASED AND PB-BASED CUPRATES
(1994-02-01)
KU, HC
;
LAI, CC
;
SHIEH, JH
;
LIOU, JW
;
WU, CY
Magnetic ordering among Pr ions occurs at a relatively high temperature of 17 K in PrBa2Cu3O7, but is absent in Pr2CuO4 and Bi2Sr2PrCu2O8 above 1.6 K. This work extends the study of magnetic properties to other Pr-containing cuprates including TlBa2PrCu2O7, (Pb.6Cu.4)Sr2PrCu2O7 and Pb2Sr2PrCu3O8. Low temperature calorimetric and SQUID measurements show broad peaks in C and dchi/dT in all cases. The onset temperatures are near 10 K, while the maxima in C as well as minima in dchi/dT prevail at about 8 to 5 K. The heat capacity data provides additional information concerning the entropy associated with the magnetic anomalies and large contributions seemingly linear with temperature.
MAGNETIC-ORDERING OF PR AND CU IN TLBA2PRCU2O7-Y
(1994-05-01)
HSIEH, WT
;
CHANG, KJ
;
LI, WH
;
LEE, KC
;
LYNN, JW
Neutron-scattering measurements have been performed to study the magnetic ordering of Pr and Cu in semiconducting TlBa2PrCu2O7-y. This compound has a nuclear structure which is similar to that of YBa2Cu3O7 but with the CuO-chain layers fully replaced by TlO layers. At low temperatures the magnetic diffraction pattern reveals magnetic Bragg peaks of the {1/2 1/2 1/2} type, which are associated with the antiferromagnetic ordering of the Pr moments. The magnetic structure consists of nearest-neighbor spins along all three crystallographic directions being antiparallel. The spin direction is along the c axis, with a saturated moment of 1.05 mu(B). The temperature dependence of the intensity of these reflections indicates a Neel temperature T(N) almost-equal-to 8 K, which is about half that observed in the related PrBa2Cu3O7 system. A second set of magnetic reflections, of the {1/2 1/2 1} type, are also observed, and these are associated with the Cu magnetic sublattice. This magnetic structure is identical to the ''plane ordering'' observed in the related 1:2:3 system, where the nearest-neighbor Cu spins are again antiparallel. The spin direction is in the tetragonal ab plane, with a saturated ordered moment of 0.59 mu(B). The temperature dependence indicates a Neel temperature of almost-equal-to 370 K for the Cu spins.
MAGNETIC-PROPERTIES OF TLBA2MCU2O7 COMPOUNDS (M=Y AND RARE-EARTH ELEMENTS)
(1994-02-01)
FUJIWARA, K
;
KAWAHARA, N
;
SUZUKI, T
;
KAMAGAI, K
;
LAI, CC
Hyperfine field and quadrupole frequency at the Cu sites have been obtained by analysis of Cu-63/65-NMR spectrum in insulating cuprate TlBa2MCu2O7 (M=Y and rare earth elements). We discuss the effect of rare earth-ion-substitution on magnetic properties of the Cu planer sites.
STRUCTURE OF THE NEW TLBA2PRCU2O7-X BY RIETVELD ANALYSIS
(1993-12-01)
LEE, TJ
;
FUN, HK
;
WANG, A
;
CHOU, CH
;
LAI, CC
The crystalline structure of new TlBa2PrCu2O7-y was obtained at room temperature from X-ray powder diffraction with CuKalpha radiation using Rietveld analysis. TlBa2PrCu2O7-x is semiconducting at room temperature with a TlBa2CaCu2O7 type (1212) structure (space group P4/mmm) and cell parameters a = 3.91836(3) angstrom, c = 12.5498(2) angstrom. The structure was refined for 15 parameters to R(wp) = 6.89 %, R(p) = 5.09 % for 6323 step intensities and R(b) = 13.24 % for 138 reflections.
STRUCTURES AND ANTIFERROMAGNETIC PR ORDERING MECHANISM OF TL(BA2-XSRX)PRCU2O7-Y COMPOUNDS BY RIETVELD ANALYSIS
(1994-04-10)
FUN, HK
;
YANG, P
;
LAI, CC
;
KU, HC
;
LEE, TJ
The crystalline structures of Tl(Ba2-xSrx)PrCu2O7-x (x=0, 0.4, 0.8, 1.0, 1.2, 1.6, 2) were obtained at room temperature (300 K) and low temperature (100 K) from X-ray powder diffraction with Cu Kalpha radiation using Rietveld analysis. Tl(Ba2-xSrx)PrCu2O7-x has an isotypical structure with TlBa2CaCu2O7(1212) at 300 and 100 K, i.e., the tetragonal system, space group P4/mmm, Z=1. The relationships between the Pr-O(1) bond lengths and the O(1)-Pr-O(1) bond angles with the antiferromagnetic ordering temperature T(n) (Neel temperature) are discussed. The mechanism of the decrease in the antiferromagnetic ordering temperature T(n) as well as the nonsuperconductivity of this system are explained using the Pr(4f) and O(2p) orbital hybridization and the Pr-O(1) bond lengths. The suggested mechanism of Pr-Pr coupling (interplanar Pr-Pr distance) for the Pr ordering by a previous study is inconsistent with our experimental results.