Strain coupling mechanisms and elastic relaxation associated with spin state transitions in LaCoO <sub>3</sub>

Zhang, Zhiying and Koppensteiner, Johannes and Schranz, Wilfried and Prabhakaran, Dharmalingam and Carpenter, Michael A. (2011) Strain coupling mechanisms and elastic relaxation associated with spin state transitions in LaCoO <sub>3</sub>. Journal of Physics: Condensed Matter, 23 (14). p. 145401. DOI 10.1088/0953-8984/23/14/145401

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Abstract

Advantage is taken of the wealth of experimental data relating to the evolution with temperature of spin states of Co3 + in LaCoO3 in order to undertake a detailed investigation of the mechanisms by which changes in electronic structure can influence strain, and elastic and anelastic relaxations in perovskites. The macroscopic strain accompanying changes in the spin state in LaCoO3 is predominantly a volume strain arising simply from the change in effective ionic radius of the Co3 + ions. This acts to renormalize the octahedral tilting transition temperature in a manner that is easily understood in terms of coupling between the tilt and spin order parameters. Results from resonant ultrasound spectroscopy at high frequencies (0.1–1.5 MHz) reveal stiffening of the shear modulus which scales qualitatively with a spin order parameter defined in terms of changing Co–O bond lengths. From this finding, in combination with results from dynamic mechanical analysis at low frequencies (0.1–50 Hz) and data from the literature, four distinctive anelastic relaxation mechanisms are identified. The relaxation times of these are displayed on an anelasticity map and are tentatively related to spin-spin relaxation, spin-lattice relaxation, migration of twin walls and migration of magnetic polarons. The effective activation energy for the freezing of twin wall motion below ~ 590 K at low frequencies was found to be 182 ± 21 kJ mol − 1 (1.9 ± 0.2 eV) which is attributed to pinning by pairs of oxygen vacancies, though the local mechanisms appear to have a spread of relaxation times. It seems inevitable that twin walls due to octahedral tilting must have quite different characteristics from the matrix in terms of local spin configurations of Co3 + . A hysteresis in the elastic properties at high temperatures further emphasizes the importance of oxygen content in controlling the properties of LaCoO3.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA62;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 23
Page Range: p. 145401
Identification Number: 10.1088/0953-8984/23/14/145401
Depositing User: Sarah Humbert
Date Deposited: 25 Mar 2011 14:25
Last Modified: 23 Jul 2013 10:02
URI: http://eprints.esc.cam.ac.uk/id/eprint/2044

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