Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

9C,12C/2005G198

EXAFS study of filled skutterudites PrOs4Sb12 and LaOs4Sb12
Kiyofumi NITTA1, Daisuke KIKUCHI2, Takafumi MIYANAGA*1, Katsuhiko TAKEGAHARA1,Hitoshi SUGAWARA3 and Hideyuki SATO2
1Department of Advanced Physics, Faculty of Science and Technology, Hirosaki University, Hirosaki,Aomori 036-8561, Japan
2Graduate School of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo
192-0397, Japan
3Department of Physics, Faculty of Integrated Arts and Sciences, Tokushima University, 1-1
Minamijosanjima-cho, Tokushima, 770 Japan
Introduction
The filled-skutterudite PrOs4Sb12 is well known to be
the first Pr compound that shows the heavy fermion
superconductivity. The superconductivity of this material
is not belong to s-wave type and expected to be new
anisotropic type superconductivity. This interesting
phenomenon is known to come from rattling motion of Prion in the Os4Sb12 cage, which suggested by the ultrasonicmeasurement [1]. Cao et al. have presented the XAFS
result for this compound [2]. They reported Debye-Waller
factor for Pr-Sb atomic pair is larger than that for Os-Sbatomic pair in the cage. We measured Pr LIII- and Os LIIIedge XAFS for PrOs4Sb12 and further La LIII- and Os LIIIedge for LaOs4Sb12 to comparethe motion of the center
atom in the cage.
Experimental
Pr LIII- (5.96keV), La LIII- (5.48keV) and Os LIII(10.9keV) edge X-ray absorption spectra were obtainedfor PrOs4Sb12 and LaOs4Sb12 powders at beam line BL-9C
and BL-12C. The measurements were performed intransmission mode at temperature ranging from 25K to300K.
Results and Discussion
Figure1 (a) shows temperature dependence of 2ndorder cumulant or Debye-Waller factor C2 for PrOs4Sb12
and LaOs4Sb12. Cao et al. have presented the XAFS result
for this compound: They reported Debye-Waller factor for
Pr-Sb atomic pair is larger than that for Os-Sb atomic pairin the cage. We confirmed that the atomic pairs contained
center atom in the cage had larger C2 values than that of
Os-Sb (cage) atomic pair. And Fig.1 (a) shows that Pr
atomic pairs have larger C2 values than that of La atomicpairs. It is interesting that the temperature dependence ofC2 cannot be fitted by Einstein curve, but the behavior
should be considered as the atomic pair has a double-wellpotential discussed in the theoretical calculation [3].
Figure1 (b) shows temperature dependence ofexperimental and theoretically calculated 3rd order
cumulant C3 for Pr-Sb atomic pair. It is characteristic
behavior that C3 has maximum point around 150K for thisatomic pair. From the theoretical study, a diatomic system
which has a double-well interatomic potential is expected
to show such a behavior. In the case that atomic potential
is asymmetry, the maximum temperature of C3 is almost
the same as the temperature height of potential barrier intheinteratomic double-well potential. By fitting
theoretical calculation to experimental data, we obtained

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the barrier and width between two wells of Pr-Sb
interatomic potential to be 0.025eV and 0.32Å,respectively.

Figure1. (a) Temperature dependence of C2 for
PrOs4Sb12 and LaOs4Sb12 and (b) temperature dependenceof experimental and theoretically calculated C3 for Pr-Sb
atomic pair.
References[1] T. Goto, Y. Nemoto, K. Sakai, T. Yamaguchi, M.
Akatsu, T. Yanagisawa, H. Hazama, K. Onuki, H.
Sugawara and H. Sato, Phys. Rev. B 69 180511 (2004).
[2] D. Cao, F. Bridges, S. Bushart, E. D. Bauer, and M. B.
Maple, Phys. Rev. B 67, 180511(2003).
[3] K.Nitta, T. Miyanaga, T. Fujikawa, J. Phys. Soc. Jpn
75, 054603(2006)*takaf@cc.hirosaki-u.ac.jp