Strain relaxation mechanisms of elastic softening and twin wall freezing associated with structural phase transitions in (Ca,Sr)TiO3 perovskites

Perks, N. J. and Zhang, Zhiying and Harrison, R. J. and Carpenter, M. A. (2014) Strain relaxation mechanisms of elastic softening and twin wall freezing associated with structural phase transitions in (Ca,Sr)TiO3 perovskites. Journal of Physics: Condensed Matter, 26 (50). p. 505402. ISSN 0953-8984 DOI 10.1088/0953-8984/26/50/505402

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Abstract

Resonant ultrasound spectroscopy has been used to measure the bulk modulus (K), shear modulus (G) and acoustic dissipation of polycrystalline perovskite samples across the CaTiO3–SrTiO3 solid solution in the temperature range ~10–1350 K. A remarkable pattern of up to ~25% softening of G as a function of both temperature and composition is due to coupling of shear strain with order parameters for the Pm 4/mcm, I4/mcm ↔ Pnma and I4/mcm ↔ Pbcm transitions. Anomalies in K associated with the phase transitions are small, consistent with only weak coupling of octahedral tilting order parameter(s) with volume strain. A change from tricritical character for the Pm 4/mcm transition towards second order character at Sr-rich compositions appears to be due to changing properties of the soft optic mode rather than to changes in magnitude of strain/order parameter coupling coefficients. Precursor softening of G ahead of the Pm 4/mcm transition, due to fluctuations or clustering, occurs over a temperature interval of up to ~200 K, and also changes character at the most Sr-rich compositions. The tetragonal structure with Sr-rich compositions is characterized by additional softening with falling temperature which is most likely related to the proximity of a ferroelectric instability. The I4/mcm ↔ Pnma transition is accompanied by stiffening, which is attributed to the effects of strong coupling between order parameters for M-point and R-point tilting. The pattern of attenuation at RUS frequencies in the tetragonal phase can be understood in terms of the mobility of twin walls which become pinned below ~500 K, and the loss mechanism most likely involves local bowing of the walls by lateral motion of ledges rather than the advance and retraction of needle tips. Twin wall mobility is suppressed in the orthorhombic structure.

Item Type:	Article
Uncontrolled Keywords:	2014AREP; IA68;
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences 07 - Gold Open Access
Journal or Publication Title:	Journal of Physics: Condensed Matter
Volume:	26
Page Range:	p. 505402
Identification Number:	10.1088/0953-8984/26/50/505402
Depositing User:	Sarah Humbert
Date Deposited:	22 Dec 2014 18:32
Last Modified:	22 Jan 2015 13:27
URI:	http://eprints.esc.cam.ac.uk/id/eprint/3181

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