Photon Factory Activity Report 2014 #32 (2015) B
BL-8A/2010G501, BL-7C/2010G502,

Structural and electronic properties of Mn hexacyanoferrates against LiTomiyuka Matsuda, Yutaro Kurihara1 and Yutaka Moritomo1,2
Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305-8571, Japan
2
Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba,
Tsukuba305-8571, Japan
1

1 Introduction
Recently, Okubo et al.[1] reported the reversible Li ion
intercalation properties in K0.14Mn1.43[Fe(CN)6]·6H2O andWe
havealso
Rb0.7Mn1.15[Fe(CN)6]·2.5H2O.
demonstrated
thatathinfilmofLi1.32Mn[Fe(CN)6]0.83·3.5H2O shows a large charge
capacity (= 128 mAh/g) as well as excellent
cyclability,[2] which indicates that the Prussian blue
analogues are one of the promising cathode materials for
the Li ion secondary batteries. In this Li ion intercalation
process, MnII/MnIII reduction/oxidation occurs and thecooperative Jahn-Teller instability can be expected. In
this work, we prepared two LixMn[Fe(CN)6]y·zH2O,
which have different amount of [Fe(CN)6] vacancy sites
and investigated the electronic states and structuralproperties.

DEC, and carefully removed from the ITO glasses. The
obtained powders were sealed in 300 µm glass capillaries.
XRD patterns were measured at 300 K and the exposure
time was 5 min. Wavelength of the X-ray was 0.77516 Å.
The lattice constants of each compounds were refined by
the RIETAN-FP program [4].
3 Results and Discussion

2 ExperimentThin films of Na1.32Mn[Fe(CN)6]0.83·3.5H2O were
electrochemically synthesized on an indium tin oxide(ITO) transparent electrode under potentiostatic
conditions at −0.50 V vs a standard Ag/AgCl electrode in
an aqueous solution containing K3[Fe(CN)6] (1.0 mmoldm−3), MnCl2·6H2O (1.5 mmol dm−3), and NaCl (1 moldm−3). Before the film growth, the surface of the ITO
electrode was purified by electrolysis of water for 3–5
min. The obtained film was transparent with a thicknessof around 1 µm. Chemical compositions of the films weredetermined by the inductively coupled plasma (ICP)
method and CHN organic elementary analysis (PerkinElmer 2400 CHN Elemental Analyzer). The Na ions were
electrochemically substituted by Li ions, using lithium
metal as the reference and counter electrode, and ethylene
carbonate (EC) / diethyl carbonate (DEC) solution
containing LiClO4 (1 mol dm−1) as an electrolyte. Thus,
we obtained LixMn[Fe(CN)6]0.83·3.5H2O (LMF83).
The electronic states of the Mn and Fe sites of LMF83
against x were determined by the ex-situ X-ray absorption
spectra (XAS) around the Mn and Fe K-edge. The XAS
measurements were conducted at the beamline 7C of thePhoton Factory, KEK. The XAS spectra were recorded bya Lytle detector in a fluorescent yield mode with aSi(111) double-crystal monochromator at 300 K. The
background subtraction and normalization wereconducted by ATHENA program [3].
The ex-situ powder X-ray diffraction (XRD)
measurements of LxMF83, and LMF87 against x wereperformed at the beamline 8A of KEK-PF, equipped with
an imaging plate detector. The samples were washed with

Figure 1. Voltage dependence on Li ion concentration (x) ofLxMF83. The arrows indicate x for the XAS measurements

Figure 1 shows the voltage against Li metal dependence
on x of LMF83 during the Li ion intercalation process.
Here, the possible x regions are 0 ≤ x ≤ 1.32 for LMF83
due to the charge neutrality. On both films, theelectrochemical reactions were observed at around 3.8,
and 3.4 V.

Figure 2. Mn K-edge XAS spectra of LMF83.

Figure 2 shows the Mn K-edge XAS spectra of LxMF83
against x. The peak around 6549 eV, which is ascribed toMnII, was observed in the whole-x region. On the contrary,
the shoulder peak around 6552 eV, which is ascribed toMnIII, was observed in the small-x region. These spectraindicates the reduction/oxidization of Mn (high-spin MnII,and high-spin MnIII) occurs in the small-x region. Figure 3

Photon Factory Activity Report 2014 #32 (2015) B
shows the Fe K-edge XAS spectra of LxMF83 against x.
The absorption peak energies (E) in the Fe K-edge spectra
show clear blue shift with decrease in x, and saturate
below x = 0.41. These data indicates blue shift is ascribedto the oxidization of Fe (low-spin FeII → low-spin FeIII),and indicates the reduction/oxidization of Fe takes placein the large-x region. Considering the formula and therange of x, the reduction/oxidization of Fe occurs in 0.49
≤ x ≤ 1.32 region, while the reduction/oxidation of Mnoccurs in 0 ≤ x ≤ 0.49 region in LMF83. Hence, the firstplateau in Figure 1 corresponds to the Mn3+/Mn2+reduction process, and the second plateau in Figure 1
corresponds to [FeIII(CN)6]3−/[FeII(CN)6]4− reduction
process.

to the larger ionic radius of high-spin MnII (0.83 Å) thanhigh-spin MnIII (0.645 Å).
Acknowledgement (option)
This work was supported by a Grant-in-Aid (21244052)
for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology. Elementaryanalysis was performed at Chemical Analysis Division,
Research Facility Center for Science and Engineering,
University of Tsukuba.
References[1] M. Okubo, et al., J. Phys. Chem. Lett. 1, 2063 (2010).
[2] T. Matsuda and Y. Moritomo, Appl. Phys. Express 4,047101 (2011).
[3] B. Ravel and M. Newville, J. Synchrotron Radiat. 12, 537(2005)[4] F. Izumi and K. Momma, Solid State Phenom. 130, 15(2007).

* moritomo.yutaka.gf@u.tsukuba.ac.jp

Figure 3. Fe K-edge XAS spectra of LMF83.

Figure 4. (a) The powder XRD patterns for LMF83. (b)Magnified patterns around the 200 reflection. The ticks indicate
the reflection peak positions. The wavelength of the X-ray is0.77516 Å.

Figure 4(a) shows the XRD patterns of LMF83. The
peak patterns are all similar, which indicates that thelattice structure remains the face-centered cubic (Fm3m;Z = 4) throughout whole x region. Figure 4(b) shows themagnified patterns around the 200 reflection. Thereflection shifts to the lower-angle side with x above x =0.41, while it shifts to the higher-angle side with x above
x = 0.41. The value of x = 0.41 is close to the value of x =0.49 where reduction/oxidation switch between Mn andFe occurs. In the reduction/oxidation of Fe region (0.49 ≤x ≤ 1.32), the lattice constants decreases with x. Thedecrease is ascribed to the smaller size of [FeII(CN)6]4− ascompared with that of [FeIII(CN)6]3−. In thereduction/oxidation of Mn region (0 ≤ x ≤ 0.49), thelattice constants increase with x. The increase is ascribed