Browsing by Author "LEE, TJ"

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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.
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.