Photon Factory Activity Report 2016 #34 (2017)

BL-2A/2015G577, 2015S2-005

Changes in the electronic state of SrCeO3 thin films
by PVDF-mediated fluorination
Takaaki Shiina1,*, Akira Chikamatsu1, Makoto Minohara2,
Hiroshi Kumigashira2 and Tetsuya Hasegawa1
Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki 305-0801, Japan

3 Results and Discussion
From the EDS measurements of the SrCeO3 precursor
and fluorinated films, we confirmed that the cation ratioof Sr and Ce was unchanged before and after thefluorination. Meanwhile, fluorine was doped and oxygen
was completely removed from the film after the reaction.
Figure 1 shows the XRD patterns of the SrCeO3
precursor and fluorinated films. The precursor film had
perovskite structure with the c-axis length of 0.429 nm.
After the fluorination, each XRD peak of the film moved
to higher 2θ, indicating that the crystal structure of thefilm transformed into fluorite structure with the c-axis
length of 0.588 nm.
Figure 2 shows the Ce M-edge XAS spectra of theSrCeO3 precursor and fluorinated films. The Ce M4 andM5 peaks were clearly observed in all spectra. The spectraof the precursor and fluorinated films are similar to thoseof the Ce4+Cl62- and Ce3+Cl63- references [4], respectively,
in both peak shapes and positions. This indicates that theFluorinated Films* STO

10Precursor Films
203040*50

SrCeO3006

SrCeO3004*Film004

Film002
SrCeO3002

2 Experiment
Perovskite SrCeO3 precursor thin films weredeposited on SrTiO3 (001) substrates using pulsed laserdeposition. The obtained films were subjected to thesubsequent reaction with PVDF pellets at 430°C for 1 hin a tubular furnace under Ar gas flow. Crystal structures
were characterized by X-ray diffraction (XRD), andchemical compositions were analyzed by energy
dispersive X-ray spectrometry (EDS). The oxidation
states of Ce were evaluated by X-ray absorption
spectroscopy (XAS) measurements, which wereperformed at the BL-2A beamline of the Photon Factory,
KEK. The XAS spectra were measured by the total
electron-yield method at 300 K.

oxidation states of Ce in the film changed from 4+ to 3+
through the fluorination. From these results, the chemicalcomposition of the fluorinated film can be inferred as
SrCeF5.

Log Intensity (arb. units)

1 Introduction
Topotactic fluorination of metal oxides with
polyvinylidene fluoride (PVDF) is an effective way tosynthesize metal oxyfluorides without forming undesired
impurity phases [1]. Our previous research revealed that
topotactic fluorination of the single crystalline thin filmsof SrCoO2.5 and BaBiO3 using PVDF can reduce Co andBi in the films together with fluorine substitution [2,3]. In
this study, we performed topotactic fluorination of single
crystalline thin films of perovskite SrCeO 3 with Ce4+. In
general, Ce ions favor Ce3+ and Ce4+ states and thus thefluorinate of SrCeO3 with PVDF might accompany thereduction of Ce oxidation state.

60

*7080

2θ (deg.)
Fig. 1: X-ray diffraction patterns of the SrCeO3
precursor and fluorinated films.
Ce M5

Intensity (arb. units)1

T = 300KCe M4Fluorinated
Films

Ce M5

Ce M4
4+4+Ce satellite

880

890

900

Ce satellite
Precursor
Films
910

920

Photon Energy (eV)Fig. 2: Ce M-edge XAS spectra of the SrCeO3
precursor and fluorinated films.

References[1] F. J. Berry et al., Solid State Commun. 134, 621(2005).
[2] T. Katayama et al., J. Sol-Gel Sci. Technol. 73, 527(2015).
[3] K. Kawahara et al., 76th JSAP Autumn Meeting, 13p2Q-10 (2015).
[4] M. W. Löble et al., J. Am. Chem. Soc. 137, 2506
(2015).
*shiina@chem.s.u-tokyo.ac.jp