• Agostinho Moreira, Ja
• Chaves, Mr
• Correia, Tm
• Gregora, I.
• Almeida, A.
• Okhay, O.
• Tkach, A.
• Vilarinho, Pm
• Petzelt, J.

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.

Topics

• impedance spectroscopy
• phase
• Strontium
• ceramic
• vacancy
• light scattering