resumo
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.
palavras-chave
K PHASE-TRANSITION; SOFT PHONON MODES; STRONTIUM-TITANATE; OPTICAL-PHONON; DOPED SRTIO3; CERAMICS; BEHAVIOR; SPECTROSCOPY; SCATTERING; HALIDES
categoria
Materials Science; Metallurgy & Metallurgical Engineering
autores
Tkach, A; Correia, TM; Almeida, A; Moreira, JA; Chaves, MR; Okhay, O; Vilarinho, PM; Gregora, I; Petzelt, J
nossos autores
Oleksandr Tkach
Investigador Auxiliar
Olena Okhay
Bolseiro de pós-Doutoramento
Paula Maria Lousada Silveirinha Vilarinho
Vice-DiretorProjectos
Propriedades dieléctricas e dinânica da rede de materiais granulantes (POCTI/CTM/45284/2002)
agradecimentos
This work was supported by the Portuguese Foundation for Science and Technology FCT (Project POCTI/CTM/45284/2002, Scholarship SFRH/BPD/34607/2007), the Academy of Sciences of the Czech Republic (Project KAN301370701) and the Science Foundation of the Czech Republic (Project AVOZ10100520).