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Anomalous behavior of displacement correlation function and strain in lanthanum cobalt oxide analyzed both from X-ray powder diffraction and EXAFS data

Published online by Cambridge University Press:  28 February 2017

V. Efimov ,
V. Sikolenko ,
I. O. Troyanchuk ,
D. Karpinsky ,
E. Efimova ,
S. I. Tiutiunnikov ,
B. N. Savenko ,
D. Novoselov  and
D. Prabhakaran
V. Efimov*
Affiliation:
Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia
V. Sikolenko
Affiliation:
Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia REC “Functional nanomaterials” Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia
I. O. Troyanchuk
Affiliation:
Scientific-Practical Material Research Center NAS Belarus, 220072 Minsk, Belarus
D. Karpinsky
Affiliation:
Scientific-Practical Material Research Center NAS Belarus, 220072 Minsk, Belarus
E. Efimova
Affiliation:
Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia
S. I. Tiutiunnikov
Affiliation:
Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia
B. N. Savenko
Affiliation:
Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia
D. Novoselov
Affiliation:
M.N. Miheev Institute of Metal Physics, S.Kovalevskoy 18, 620990 Ekaterinburg, Russia Department of Physics, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
D. Prabhakaran
Affiliation:
Department of Physics, University of Oxford, OX1 3PU Oxford, United Kingdom
*
a)Author to whom correspondence should be addressed. Electronic mail: [email protected]
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Abstract

A combined X-ray powder diffraction (XPD) and high-resolution extended X-ray absorption fine structure (EXAFS) at the Co and Ga K-edges study has been performed for LaCoO3 and LaGaO3 ceramics, the latter sample was used as a reference without spin transitions. Based on the X-ray diffraction data, we have found that isotropic atomic displacement parameters (ADP) or mean-squared displacement of the Co–O bond exhibit gradual growth below ~50 K, wherein the strain dependencies testify rapid increase below 150 K for the LaCoO3 having rhombohedral structure. No similar features could be observed for LaGaO3 sample. Above ~100 K the isotropic ADP of the Co–O bond indicate a gradual growth, whereas strain curves show distinct bend near the spin-state transition temperature at about 150 K. According to the EXAFS data, the correlated parallel mean squared relative displacement (MSRD||) of Co–O and Ga–O bonds exhibit a gradual growth above 150 K; however, in the LaCoO3 this parameter is notably bigger. It is supposed that at low temperature the cobalt ions are dominantly in low-spin (LS) state, while certain amount of Co3+ ions located within the surface layer of the crystallines have high-spin state (HS). Temperature growth leads to a gradual transformation of the HS state of the cobalt ions into the highly-hybridized intermediate-spin (IS) state, while the cobalt ions located in the inner part of the crystallines remain LS configuration up to 150 K. Further temperature increase leads to a spin transition of the Co3+ ions located within the crystallines from the LS state into the IS one.

Keywords

diffractionEXAFScobaltites
Type
Technical Articles
Information
Powder Diffraction , Volume 32 , Supplement S1 , September 2017 , pp. S151 - S154
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Copyright
Copyright © International Centre for Diffraction Data 2017 

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