Abstract
Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La 3+, Gd 3+, Y 3+), which substitute Sr 2+ 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 ∼1.547 Å was estimated, which is ∼7% larger than the Sr 2+ radius. The vacancy size obtained can directly explain the increase in lattice parameter with increasing Bi 3+ content in Bi-doped STO, as opposed to the dopants referred to above. Furthermore, the introduction of La 3+, Gd 3+ or Y 3+ ions at the Sr site causes a considerable stiffening of the transverse optic TO 1 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.
Published Version
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