Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed MatterCo and Ni 3d States of Al72Ni12Co16 Quasicrystal

2C/2004G198

1Manabu Inukai1, Hidetoshi Miyazaki, Shunji Ota1, Takaharu
Suzuki1, MasahikoKato1, Sinya Yagi1,1
2
3
Kazuo Soda* , Yasuhisa Tezuka , Yoshihiko Yokoyama
1
Graduate
SchoolofEng., Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2
Facultyof
ScienceandTechnology, Hirosaki University, Bunkyo-cho, Hirosaki 036-8561, Japan
3
Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, JapanIntroduction
Decagonal Al-Ni-Co quasicrystals show the unique
two-dimensional atomic arrangement and unusual electric
properties [1]. The origin of these features has not beenclarified well yet. According to a theoretical calculation[2], a strong Co-Al interaction may cause the large
increase in the binding energy EB of their Co 3d states,
which is unusually higher than the Ni 3d states. Thus, wehave investigated the energy distributions of their 3dstates by the 3d-2p x-ray emission (XES) spectroscopy,using the synchrotron radiation as an excitation source,which may reduce the experimental errors in the photonenergy calibration of the XES spectrum.

arrangement of the lower cluster. However, the Ni and Co
3d bands in the cluster are largely separated. Further
study is in progress for a cluster with a possible random
occupation of Co and Ni at the transition metal site.
References[1] Z.M. Stadnik ed., Physical Properties of Quasicrystals,(Springer-Verlag, Berlin, 2000).
[2] M. Kraj i et al., Phys. Rev. B 62, 243 (2000).
[3] H. Adachi et al., J. Phys. Soc. Jpn., 45, (1978) 875.
[4] K. Hiraga et al., Mater. Sci. Eng. A312, 1 (2001).
*j45880a@nucc.cc.nagoya-u.ac.jp

Experimental
The XES measurement was performed at BL-2C of
Photon Factory for a single-grain decagonal quasicrystal
Al72Ni12Co16. The photon energy of the XES spectrum iscalibrated with the elastically scattered photons, whoseenergy is determined by measuring the photoelectron
spectrum of Au. The binding energies of the relevant corelevels were obtained by the hard x-ray photoelectron
measurement at BL47XU of SPring-8.
Results and Discussions
Figure1 shows the Co and Ni 3d−2p XES spectra ofAl72Ni12Co16 recorded at the excitation photon energy of841.43 and 922.96 eV, respectively, in comparison to avalence-band x-ray photoelectron (XPS) spectrum. While
the XPS spectrum exhibits a single-peaked transition
metal 3d band at EB = 2 eV, the XES spectra clearly showthat the band consists of the Ni and Co 3d states and that
the Ni 3d band is located at EB ~ 2.2 eV, higher than theCo 3d one. The present result seems inconsistent with thetheoretical prediction [2].
Figure2 shows the electronic structures calculated by aDV-Xα method [3] for Al60Ni20Co20 clusters presented in
the insets. The atomic arrangement in these clusters isbased on a model proposed by Hiraga et al. [4]; thecluster consists of two layers separated by 0.2 nm and theinnermost atomic ring is composed of Ni and Co in theupper and lower clusters, respectively. Although thecalculated electronic bands have ∼1eV higher energy thanthe experimental one, their overall features are consistent
with those for the large approximant [1]; a pseudogapnear the Fermi level (EB ∼ −1eV in the cluster calculation)
for the Al-derived states and a single transition-metal dband. The present XES spectra might suggest the atomic

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Users' Report

Fig.1 3d-2p XES and Valence-band XPS spectra ofdecagonal quasicrystal Al72Ni12Co16.

Fig. 2 Density of states for Al60Ni20Co20 clusters shown in
the insets. Large and small symbols in the insets
represent atoms (Al: open circle, Ni: closed circle, andCo: hatched circle) in the first and second layers of thecluster, respectively.