Abstract
A combined high-resolution Co K-edge extended x-ray absorption fine structure (EXAFS) and high-resolution X-ray powder diffraction (XRD) study has been performed to clarify the detail of anomalous behavior of temperature-dependent magnetic susceptibility curve on the LaCoO3 across the spin-state (∼120 K) transition. According to XRD analysis, the Debye-Waller factor of Co-O bond exhibit rapid growth below 20 K whereas the temperature dependence of the average Co-O bond length shows linear behavior from 10 K to 400 K. The EXAFS data show an anomalous decrease of the Co-O bond lengths with respect to those obtained by XRD. No local distortion of CoO6 octahedral as temperature increases up to 400 K has been detected.
Highlights
Perovskite-like lanthanum cobalt oxide LaCoO3 is a fascinating material studied since the 1950’s with many controversial explanations of its peculiar structural [1,2], transport [3] and magnetic [4,5]properties
All observed Bragg peaks for LaCoO3 in the temperature range from 10 K to 400 K were indexed in the frame of the rhombohedral R-3c space group
The temperature dependence of MSRD|| is the set of the contributions of all normal modes and can be well approximated by the correlated Einstein model [15]
Summary
Perovskite-like lanthanum cobalt oxide LaCoO3 is a fascinating material studied since the 1950’s with many controversial explanations of its peculiar structural [1,2], transport [3] and magnetic [4,5]properties. With temperature increase a maximum of the magnetic susceptibility [4] and thermal expansion coefficient [3] was observed near 120 K whereas a second anomaly [3] followed by a plateau at 500 K ÷ 520 K is associated with the metal-insulator transition.
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