Role of trivalent Sr substituents and Sr vacancies in tetragonal and polar states of SrTiO3
authors Tkach, A; Correia, TM; Almeida, A; Moreira, JA; Chaves, MR; Okhay, O; Vilarinho, PM; Gregora, I; Petzelt, J
nationality International
journal ACTA MATERIALIA
author keywords Phase transformations; Dynamic phenomena; Raman spectroscopy; Lattice defect vacancies; Perovskites
keywords K PHASE-TRANSITION; SOFT PHONON MODES; STRONTIUM-TITANATE; OPTICAL-PHONON; DOPED SRTIO3; CERAMICS; BEHAVIOR; SPECTROSCOPY; SCATTERING; HALIDES
abstract Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La3+, Gd3+, Y-3+), which substitute Sr2+ ions. An extraordinary shift of the antiferrodistortive transition temperature (T-a) is ascertained when just a small percentage of any of the dopants is used. T-a is dependent on the tolerance factor (t). In this work, it is clearly shown that, regardless of the dopant used, a common linear dependence of T-a vs. t is obtained if strontium vacancies are taken into account. A vacancy size of similar to 1.547 angstrom was estimated, which is similar to 7% larger than the Sr2+ radius. The vacancy size obtained can directly explain the increase in lattice parameter with increasing Bi3+ content in Bi-doped STO, as opposed to the dopants referred to above. Furthermore, the introduction of La3+, Gd3+ or Y3+ ions at the Sr site causes a considerable stiffening of the transverse optic TO1 mode at low temperatures, thereby decreasing the phonon contribution to the dielectric permittivity. Thus, no traces of a ferroelectric phase are found for any of the dopants used in this work. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
publisher PERGAMON-ELSEVIER SCIENCE LTD
issn 1359-6454
year published 2011
volume 59
issue 14
beginning page 5388
ending page 5397
digital object identifier (doi) 10.1016/j.actamat.2011.05.011
web of science category Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering
subject category Materials Science; Metallurgy & Metallurgical Engineering
unique article identifier WOS:000294091400002
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journal impact factor 7.656
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