Elastic and anelastic relaxations in the relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 : II. Strain–order parameter coupling and dynamic softening mechanisms

Carpenter, M. A. and Bryson, J. F. J and Catalan, G. and Zhang, S J and Donnelly, N J (2012) Elastic and anelastic relaxations in the relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 : II. Strain–order parameter coupling and dynamic softening mechanisms. Journal of Physics: Condensed Matter, 24 (4). 045902. DOI 10.1088/0953-8984/24/4/045902

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Abstract

Elastic and anelastic behaviour of single crystal and ceramic samples of Pb(Mg1/3Nb2/3)O3 has been investigated at frequencies of ~0.1–1.2 MHz through the temperature interval 10–800 K by resonant ultrasound spectroscopy (RUS). Comparison with data from the literature shows that softening of the shear modulus between the Burns temperature and the freezing interval is independent of frequency. The softening is attributed to coupling between acoustic modes and the relaxation mode(s) responsible for central peaks in Raman and neutron scattering spectra below the Burns temperature, and can be described with Vogel–Fulcher parameters. Shear elastic compliance and dielectric permittivity show similar patterns of temperature dependence through the freezing interval, demonstrating strong coupling between ferroelectric polarization and strain such that the response to applied stress is more or less the same as the response to an applied electric field, with a frequency dependence consistent with Vogel–Fulcher-like freezing in both cases. Differences in detail show, however, that shearing induces flipping between different twin orientations, in comparison with the influence of an electric field, which induces 180° flipping: the activation energy barrier for the former appears to be higher than for the latter. Below the freezing interval, the anelastic loss also has a similar pattern of evolution to the dielectric loss, signifying again that essentially the same mechanism is involved in the freezing process. Overall softening at low temperatures is attributed to the contributions of strain relaxations due to coupling with the local ferroelectric order parameter and of coupling between acoustic modes and continuing relaxational modes of the polar nanostructure. Dissipation is attributed to movement of boundaries between PNRs or between correlated clusters of PNRs. Overall, strain coupling is fundamental to the development of the characteristic strain, dielectric and elastic properties of relaxors.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA63; Part II
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 24
Page Range: 045902
Identification Number: 10.1088/0953-8984/24/4/045902
Depositing User: Sarah Humbert
Date Deposited: 23 Dec 2011 12:21
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2323

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