Structure–microstructure–dielectric tunability relationship in Mn-doped strontium titanate ceramics

The influence of Mn incorporation into the Sr and Ti sites of SrTiO3 ceramics on the structure, microstructure and dielectric tunability is studied in this work. For both Sr1−xMnxTiO3 and SrTi1−yMnyO3 formulations, the lattice parameter, calculated from X-ray diffraction profiles, was found to decrease with increasing Mn content, but with different rates. Transmission electron microscopy analysis indicated that the solid solubility of Mn for Sr1−xMnxTiO3 system is limited to x < 3%, while scanning electron microscopy analysis revealed a marked decrease of the grain size for SrTi1−yMnyO3 ceramic samples. The temperature range where the dielectric constant is tunable was enlarged for Sr1−xMnxTiO3 ceramics comparing with undoped SrTiO3. A higher tunability (∼70%) and quality factor (∼6000) around 75–100 K were obtained as well. It is suggested that the observed dielectric behaviour is closely related to the existence of polar microregions, formed by the introduction of Mn into the Sr site. In contrast, in SrTi1−yMnyO3 ceramics a decrease of the dielectric tunability, following a reduction of dielectric permittivity was observed.