Effect of Mg doping on the structural and dielectric properties of strontium titanate ceramics

The influence of Mg incorporation into A- and B-sites of the perovskite lattice of SrTiO₃ ceramics on the structural, microstructural and low-frequency dielectric properties is studied in this work. Compounds in the systems Sr_1-xMg_xTiO₃ and SrTi _1-yMg_yO_3-δ were synthesised by a conventional solid-state method. The solid solubility of Mg is restricted to x < 1% for A-site occupancy (Sr_1-xMg_xTiO₃) and to y < 15% for B-site occupancy (SrTi_1-yMg_yO _3-δ). The lattice parameter is found to increase with Mg content for the SrTi_1-yMg_yO_3-δ system, while it is almost invariant in the Sr_1-xMg_xTiO ₃ one. The dependence on the lattice-site occupancy is also verified for the grain growth of ceramics. For SrTi_1-yMg_yO _3-δ the average grain size markedly decreases with increasing Mg content. For Sr_1-xMg_xTiO₃ the inverse dependence is observed. Contrary to expectations, Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, located in either A-or B-sites of the SrTiO₃ lattice. Moreover, fitting the dielectric behaviour to Barrett's law demonstrates that B-site doping drives the system away from the ferroelectric instability. In Mg-doped strontium titanate ceramics the dielectric permittivity and dielectric losses decrease. The results are discussed based on the correlation between cation-site occupancy, charge and chemical stoichiometry in both systems.