Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

12C,7C/2004G086

X-ray absorption fine structure studies on La1-xSrxFeO3
U. Manju1, D. Matsumura2,3, M. Shimojo2,T. Ohta2, D. D. Sarma*1
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India.
2
Deptartment of Chemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113.
3
Synchrotron Radiation Research Center, Japan Atomic Energy Institute, Mikazuki, Sayo-gun, Hyogo
679-5148, Japan.
180

Users' Reportvalency remains essentially the same across the series.
Derivative spectra of the pre-edge region is shown in theinset (a).
Preliminary analysis of the Fe K EXAFS region wascarried out using the nearest neighbour shell. Relative
mean square displacement (RMSD) of bond lengths withrespect to temperature for various compositions areshown in the inset (b) of figure1. Fitting the data using
correlated Einstein model, Einstein frequency and relative
static mean square displacement are extracted for each xvalue. More refined data analysis is now being carried out.

W

T=25 K
Fe- K edge
La1-xSrxFeO3
with x=0-0.67(a)Absorption intensity (arb. unit)

T=25 K, Fe- K edge

(b)
7112

7114

7116

7118

7120

7122

Photon energy (eV)PS

Sr0.6727110

RMSD (.01Angstrom )Absorption intensity (arb. unit)

Introduction
The issue of metal insulator transitions (MIT) intransition metal oxides has been investigation intensely
for many decades, yet the phenomena is not completely
understood till date. One of the many ways to realise sucha transition is by doping an insulator with charge carriers,
either electrons or holes. This has been most easily
achieved by heterovalent substitution, where an ion with3+
one oxidation sate (say La ) is replaced with another ion
2+with a different oxidation state, for example Sr , as in
La1-xSrxCoO3 [1] and La1-xSrxTiO3 [2]. If the electronicsystem remains homogeneous, in spite of the inevitable
presence of chemical inhomogeneity at the microscopic
level due to chemical substitution, the parent insulating
system, say LaTiO3 or LaCoO3, should transform to ametallic state with substitutional doping. However, theextent of doping required in reality to bring about thistransition is substantial in every case, the exact amountbeing system dependent. In certain cases like La1-xSrxFeO3[3] and La1-xSrxCrO3 [4], the system remains insulating forpossible doping. Thus combining these observations withthe preceding discussion, it appears clear that electronic
inhomogeneity must play a significant role in determining
the exact nature of metal-insulator transition in suchchemically doped systems. In order to probe such effects,
we have carried out a detailed investigation of La1xSrxFeO3 employing x-ray absorption technique which is
known to be influenced by local electronic and geometricstructures.
Experiment
Polycrystalline samples of La1-xSrxFeO3 with x = 0, 0.1,0.2, 0.3, 0.4, 0.5 and 0.67 were prepared by solid statesynthesis using stoichiometric amounts of high purity
starting materials La2O3, SrCO3 and FeC2O4. 2H2O. X-ray
absorption measurements were carried out at the beamline BL-10B and BL-9A to cover the Fe K, Sr K and La
L3 absorption edges. Experiments were performed attemperatures ranging from 25 K to 300 K.
Results and discussion
Figure1 shows the Fe K-edge XANES spectra of La1xSrxFeO3 collected at 25 K. The pre-edge, shoulder andwhite line is marked by P, S and W respectively in thefigure. W and S are ascribed to dipolar 1s to np
transitions where as P is ascribed to a transition from 1sto 3d [5]. It is clear from the figure that there is no drasticchange in the spectra with hole doping. Thus, the Fe

Sr0.4
Sr0.3
Sr0.2
Sr0.1
LaFeO3050100150200250300

T (K)710071207140716071807200

Photon energy (eV)References[1] G. H. Jonker and J. H. Van Santen, Physica XIX,120 (1953).
[2] M. Imada, A. Fujimori and Y. Tokura, Rev. Mod.
Phys. 70, 1039 (1998).
[3] J. Grenier, N. Ea, M. Pouchard and MM. AbouSekkina, Mat. Res. Bull. 19, 1301 (1984).
[4] J. B. Webb, M. Sayer and A. Mansingh, Can. J.
Phys. 55, 1725 (1977).
[5] J. Herrero-Mart’in, G. Sub’ias, J. Garc’ia and M.
C. S’anchez, Phys. Rev. B 17, 4963 (2005).