Role of trivalent Sr substituents and Sr vacancies in tetragonaland polar states of SrTiO.sub.3./sub..

0366112 - FZÚ 2012 RIV GB eng J - Journal Article
Tkach, A. - Correia, T.M. - Almeida, A. - Moreira, J.A. - Chaves, M. R. - Okhay, O. - Vilarinho, P. M. - Gregora, Ivan - Petzelt, Jan
Role of trivalent Sr substituents and Sr vacancies in tetragonaland polar states of SrTiO₃.
Acta Materialia. Roč. 59, č. 14 (2011), 5388-5397. ISSN 1359-6454. E-ISSN 1873-2453
R&D Projects: GA AV ČR KAN301370701
Institutional research plan: CEZ:AV0Z10100520
Keywords : phase transformations * dynamic phenomena * Raman spectroscopy * lattice defect vacancies * perovskites
Subject RIV: BM - Solid Matter Physics ; Magnetism
Impact factor: 3.755, year: 2011
http://www.sciencedirect.com/science/article/pii/S1359645411003417

Raman scattering is used to study strontium titanate (STO) ceramics with several heterovalent dopants(La3+, Gd3+, Y3+), which substitute Sr2+ ions. Extraordinary shift of the antiferrodistortive transition temperature (Ta) is observed when a small percentage these dopants is used. A common linear dependence of Ta vs. tolerance factor t is obtained if strontium vacancies are taken into account. A vacancy size of ~1.547 A˚ was estimated, ~7% larger than the Sr2+ radius. This vacancy size can directly explain the increase in lattice parameter with increasing Bi3+ content in Bi-doped STO. 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. No traces of a ferroelectric phase are found for any of the dopants used.
Permanent Link: http://hdl.handle.net/11104/0201197