Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

4B2/2002G214, 2003G190

Crystal structure of geometrically frustrated spinel AlV2O4
Hiroki ISHIBASHI1*, Yoichi HORIBE1, Masao SHINGU2, Kosuke KURUSHIMA1,Shigeo MORI1,3, Takuro KATSUFUJI2,3
1
Osaka Prefecture Univ., Sakai, Osaka 599-8531, Japan
2
Waseda Univ., Tokyo 169-5551, Japan
3
PRESTO, Japan Science and Technology Corporation, Saitama 332-0012, Japan
Introduction
Spinel compound AlV2O4 is known to show chargeordering (CO) behavior below TCO ~ 700K [1]. Upon thephase transition at TCO, the electrical resistivity sharply
increases and the magnetic susceptibility is suppressed.
The CO state has a rhombohedrally distorted spinelstructure. A structural model reported previously is that
the V ions on the Kagome lattices and those on thetriangular lattices with different valences stack alternately
along the [111] direction. However, both x-ray powder
diffraction and electron diffraction (ED) experiments
show the presence of the superlattice structure with thewave vector q=1/2[111], which was not considered in theproposed model. In this study, we investigate the crystal
structure by high resolution x-ray powder diffraction
measurement to clarify the CO state in AlV2O4.
Experimental
The sample of AlV2O4 was prepared by the same way
as the previous report [1]. The powder diffraction
experiment at room temperature was carried out using
multiple-detector system (MDS) installed at BL-4B2
station. A flat Ge(111) analyzer was used to improve theangular resolution. The diffraction data of AlV2O4 werecollected at a step interval of 0.004° in 2θ and a counting
time of 5 sec at each step. The asymmetric 2θ scan mode
was used at a fixed incident angle of α = 7°. The
wavelength of incident beam was λ = 1.2060 Å.
Results and Discussion
Figure 1 shows the powder pattern of AlV2O4 at room
temperature. First, the lattice constants are determinedfrom the peak position of each reflection and estimated asa ~ 5.75 Å and c ~ 28.85 Å with a rhombohedral
symmetry (hexagonal axis choice). Based on thisinformation and various electron diffraction patterns, wehave constructed several structural models and thestructural refinement for each model was carried out by
Rietveld method. The structural parameters for the best
fitting model are shown in Table 1. The overall quality of
the fitting is fairly good. Further, the refined structuralmodel is consistent with the high resolution electron
microscope images [2].
Here, we discuss the CO state of AlV2O4 based on thepresent structural model. There are three independent V
sites, two V atoms (V1 and V2) on the triangular lattice andone V atom (V3) on the Kagome lattice. On the other hand,

there are four kinds of V-V bond length. Two of them areshorter (V3-V3: 2.610 Å, V2-V3: 2.809 Å) and the others
are longer (V3-V3: 3.141 Å, V2-V3: 3.039 Å). The shorter
V3-V3 bonds form “trimers” and all the V2 atoms are
sandwiched by two V3 trimers. As a result, seven V atoms
form a V cluster, i.e., “heptamer”. The stabilization of theV heptamer is consistent with the physical properties andtheoretical consideration [2].

Fig. 1. Portion of the synchrotron x-ray powder
diffraction pattern (black points) and the Rietveld
fit (red line).
Table 1. Structural parameter of AlV2O4Space group R-3m
a = 5.75148(3) Å, c = 28.85407(14) Åatom sitexyz
Al1
6c 000.18298(3)Al26c 000.30931(3)V1
3a 000V2
3b 001/2
V3
18h 0.84873(2)=1-x 0.41786(1)O1
6c 000.12132(6)O2
6c 000.37045(6)18h 0.83153(8)=1-x 0.53921(4)O3
18h 0.82972(8)=1-x 0.29034(4)
O4

β11

β22

β33

β122

B(Å )
0.146(12)0.103(11)0.259(7)=B(O1)=B(O1)=B(O1)

β13

β23

V1 0.0014(2) =β11 0.000086(8) =β11/200V2 0.0007(2) =β11 0.00176(2) =β11/200V3 0.00231(7) =β11 0.000059(2) 0.00047(8) 0.00002(1) = -β13
RWP = 7.82 %, RB = 2.10 %, S = 1.605

References[1] K. Matsuno et al., J. Phys. Soc. Jpn 70, 1456 (2001).
[2] Y. Horibe et al., submitted.
*hiroki@p.s.osakafu-u.ac.jp

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