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 Sr1-xMgxTiO3 and SrTi1-yMgyO3-delta were synthesised by a conventional solid-state method. The solid solubility of Mg is restricted to x<1% for A-site occupancy (Sr1-xMgxTiO3) and to y<15% for B-site occupancy (SrTi1-yMgyO3-delta). The lattice parameter is found to increase with Mg content for the SrTi1-yMgyO3-delta system, while it is almost invariant in the Sr1-xMgxTiO3 one. The dependence on the lattice-site occupancy is also verified for the grain growth of ceramics. For SrTi1-yMgyO3-delta the average grain size markedly decreases with increasing Mg content. For Sr1-xMgxTiO3 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.