Photon Factory Activity Report 2018 #36 (2019)

BL-4C/2017G643

Effect of Cr Substitution in Sr2V1-xCrxFeAsO3
Masamichi NAKAJIMA*, Taihei WAKIMURA, Shigeki MIYASAKA and Setsuko TAJIMA
Department of Physics, Osaka University,
1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

3 Results and Discussion
Figure 1(a) shows Cr K-edge x-ray absorption spectra
for Sr2V1-xCrxFeAsO3 with x = 0.2 as well as fourreference chromium oxides: Cr, Cr2O3, Sr2CrO4, andCaCrO4. It has been established that the energy positionof the absorption edge is shifted to higher energies as theoxidation state increases. Figure 1(b) shows the energy
derivative of the absorption spectra. We determined theedge positions by the peak energies in Fig. 1(b),corresponding to the inflection points. Clearly, the edge
positions of the reference compounds in the present study
vary linearly with the Cr valence as shown in the inset ofFig. 1(a). The edge of Sr2V1-xCrxFeAsO3 lies near that ofSr2CrO4, indicating that the valence of introduced Cratoms is 4+.
Given that the valence of V atoms is close to 3+ [3], Cr
substitution
corresponds
toelectrondoping.
Superconductivity in Sr2VFeAsO3 is not very sensitivewith Cr substitution [2], suggesting that the electron
filling is not a primary parameter determining a
superconducting transition temperature. Chemical
substitution into a blocking layer does not make a large
impact on superconductivity as long as competing orders
are absent. It should be noted that the antiferromagneticalignment of Cr3+ moments was suggested in fully
substituted compound Sr2CrFeAsO3 (x = 1) [4]. Withfurther substituting Cr above the composition investigated

5(a)43CrCr2O32 Sr2CrO410

CaCrO420

Sr2V1-xCrxFeAsO 3x = 0.2

E (eV) (arb. units)

2 Experiment
Polycrystalline Sr2V1-xCrxFeAsO3 with x = 0.2 weresynthesized by solid-state reaction starting from SrO,
SrAs2, V2O3, Cr2O3, and Fe [2]. Sample quality waschecked by x-ray diffraction and energy dispersive x-ray
spectroscopy. The Cr K-edge x-ray absorption
spectroscopy measurement was carried out at BL-4C ofPhoton Factory in KEK, Japan. Absorption spectra were
measured in the transmission mode with the energy rangeof 5980–6020 eV.

here, the Cr valence would gradually change from 4+ to3+.

1000d/dE (arb. units)

1 Introduction
Sr2VFeAsO3, an iron-based superconductor with aperovskite-type blocking layer, is characterized by asuperconducting ground state without any chemical
substitution [1]. To elucidate what parameter is a key forsuperconductivity and the physical properties, asystematic study of chemical substitution is a powerfultool. In the present study, we synthesized polycrystalline
samples of Cr-substituted Sr2V1-xCrxFeAsO3 andperformed the Cr K-edge x-ray absorption spectroscopy
to determine the valence of Cr.

2 4 6Cr valence

(b)

05980

5990

6000
6010
Energy (eV)6020

Fig. 1: (a) Normalized x-ray absorption spectra for Sr2V1xCrxFeAsO3 (x = 0.2) and reference chromium oxides.
Bars indicate the edge positions determined by theinflection point. Inset shows energy positions of the Cr Kedge with respect to the Cr metal as a function of theoxidation state. A diamond indicates Sr2V1-xCrxFeAsO3.
(b) Energy derivative of the absorption spectra. The edgeenergy was determined by the peak position.
Acknowledgement
This work was supported by JSPS KAKENHI Grant
Number JP18K13500.
References[1] X. Zhu et al., Phys. Rev. B 79, 220512(R) (2009).
[2] T. Wakimura et al., Supercond. Sci. Technol. 32,064003 (2019).
[3] H. G. Cao et al., Phys. Rev. B 82, 104518 (2010).
[4] M. Tegel et al., Europhys. Lett. 89, 37006 (2010).
* nakajima@phys.sci.osaka-u.ac.jp