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Abstract: The structure–property relations of Mg-doped SrTiO3 (ST) sol–gel thin films deposited on Pt/TiO2/SiO2/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO3. It has been predicted that Mg-doped SrTiO3 should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO3 but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05at.%). However, for Sr1−x Mg x TiO3 (SMT) (x ⩽0.30) films annealed at 750°C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900°C, the solubility limit of Mg was x =0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

Abstract: Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La3+, Gd3+, Y3+), 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 ∼1.547Å was estimated, which is ∼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. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]