Elastic relaxations associated with the Pm\bar {3} m –R\bar {3} c transition in LaAlO3: IV. An incipient instability below room temperature

Carpenter, M. A. and Buckley, A. and Taylor, P. A. and McKnight, R. E. A. and Darling, T. W. (2010) Elastic relaxations associated with the Pm\bar {3} m –R\bar {3} c transition in LaAlO3: IV. An incipient instability below room temperature. Journal of Physics: Condensed Matter, 22 (3). 035406. DOI 10.1088/0953-8984/22/3/035406

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Abstract

Resonant ultrasound spectroscopy has been used to characterize elastic softening and acoustic dissipation behaviour in single crystal and ceramic samples of LaAlO3 between 10 and 300 K. For the twinned R\bar {3} c single crystals, average values of the cubic elastic moduli \case {1}{2}(C_{11}-C_{12}) and C44 were followed while the ceramic sample provided data for the bulk and shear moduli. A Debye-like dissipation peak occurs in the vicinity of 250 K, from which an activation energy of 43 +- 6 kJ mol[?]1 has been obtained. The mechanism for this is not known, but it is associated with C44 and therefore could be related in some way to the \mathrm {cubic \leftrightarrow rhombohedral} transition at [?]817 K. Slight softening in the temperature interval {\sim } 220 \to 70 K of resonance peaks determined by shear elastic moduli hints at an incipient Eg ferroelastic instability in LaAlO3. The softening interval ends with a further dissipation peak at [?]60 K, the origin of which is discussed in terms of freezing of atomic motions of La and/or Al away from their high symmetry positions in the R\bar {3} c structure. LaAlO3 thus shows evidence of incipient structural instability at low temperatures which is potentially analogous with the phenomenologically rich behaviour of SrTiO3.

Item Type: Article
Uncontrolled Keywords: 09AREP; IA59;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 22
Page Range: 035406
Identification Number: 10.1088/0953-8984/22/3/035406
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2010 12:16
Last Modified: 23 Jul 2013 09:56
URI: http://eprints.esc.cam.ac.uk/id/eprint/1329

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