Hole Distribution of Intercalated Cuprates Using x-ray Absorption Spectroscopy

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CHINESE JOURNAL OF PHYSICS VOL. 43, NO. 3-II JUNE 2005

J. M. Chen,1, ∗ _{S. C. Chang,}2 _{R. S. Liu,}2 _{J. M. Lee,}1, 3 _{M. Park,}4 _{and J. H. Choy}4 1_{National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30077, Taiwan, R.O.C.}

2_{Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, R.O.C.} 3_{Department of Electro-Physics, National Chaio-Chu University, Hsinchu 30077, Taiwan, R.O.C.}

4_{National Nanohybrid Materials Laboratory, School of Chemistry,}

Seoul National University, Seoul 151-747, Korea

Unoccupied electronic states of X-Bi2Sr2CaCu2O8 (X-Bi2212, X = I, HgI2, and

(Py-CH3)2-HgI4, Py = pyridine) have been probed by O K-edge x-ray absorption near-edge

structure (XANES) spectra using a bulk-sensitive x-ray-fluorescence-yield technique. In the O 1s absorption edge of X-Bi2212, the pre-edge peak at ∼ 528.3 eV is attributed to transitions into the O 2p hole states located in the CuO2planes. As deduced from O K-edge

x-ray absorption spectra, the hole concentration in the CuO2 planes of X-Bi2212 increases

for X = I and HgI2, but decreases for X = (Py-CH3)2HgI4, relative to pristine Bi2212. The

present XANES results clearly demonstrate that the hole density within the CuO2 planes of

intercalated Bi2Sr2CaCu2O8 can be not only reduced but also increased, depending on the

chemical character of the intercalants.

PACS numbers: 74.62.Dh, 74.25.Jb, 74.72.Bk

I. INTRODUCTION

The intercalation of guest molecules into the high-Tc superconductive copper-oxide

materials has received considerable attention recently because of practical applications of high-Tc superconductors [1, 2]. Several new high-Tc intercalated superconductors, such

as La2CuO4−δFy [3, 4], Sr2CuO2F2+δ [5], HgBa2Sr2Cu2(CO3)O7 [6], (Hg0.3Pb0.7)Sr4Cu2

(CO3)O7 [7], (Tl0.5Pb0.5)Sr4Cu2(CO3)O7 [8], (Bi0.5Hg0.5)Sr4Cu2(CO3)O7 [9], HgBa2Ca_n−1

CunO2n+2+δFy (n = 1–3) [10], X-Bi2Sr2Cam−1CumOy (m = 1 and 2; Bi2201 and

X-Bi2212; X = I, HgI2, (Me3S)2HgI4, and (Py-CnH2n+1)2HgI4, n = 1–12, Py = pyridine)

[11, 12], have been reported. Among them, X-Bi2212 or X-Bi2201 systems have attracted extensive investigation due to their unique properties and controversial issues regarding the role of interlayer coupling on superconductivity [11–15].

The pristine Bi2212 and Bi2201 materials exhibit weakly bound Bi-O double layers, consequently enabling free expansion of the unit cell in the c direction without significantly changing other internal lattice structure [11, 12]. Various inorganic or organic modulation layers were intercalated into Bi2O2 double layers of the Bi2201 and Bi2212 materials. In

particular, long-chain organic molecules, such as (Py-CnH2n+1)2HgI4 for n = 1–12 and

(Me3S)2HgI4, were successfully intercalated into Bi-based cuprates in the form of a complex

heterostructured high-Tc superconducting nanohybrid [11, 12]. Relative to pristine Bi2212,

http://PSROC.phys.ntu.edu.tw/cjp 642 2005 THE PHYSICAL SOCIETYc OF THE REPUBLIC OF CHINA