Browsing by Author "CHOU, CH"

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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.
SOME EXACT RESULTS FOR THE DIFFUSION-COEFFICIENTS OF MAPS WITH PRUNING CYCLES
(1994-11-21)
TSENG, HC
;
CHEN, HJ
;
LI, PC
;
LAI, WY
;
CHOU, CH
For a family of piecewise linear maps, we consider several interesting cases in which the symbolic dynamics is described in terms of a restricted grammar. However, their diffusion coefficients can be determined analytically through appropriate cycle expansions.
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.