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

The influence of Mn incorporation into the Sr and Ti sites of SrTiO ₃ ceramics on the structure, microstructure and dielectric tunability is studied in this work. For both Sr_1-xMn_xTiO₃ and SrTi_1-yMn_yO₃ 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 Sr _1-xMn_xTiO₃ system is limited to x < 3%, while scanning electron microscopy analysis revealed a marked decrease of the grain size for SrTi_1-yMn_yO₃ ceramic samples. The temperature range where the dielectric constant is tunable was enlarged for Sr_1-xMn_xTiO₃ 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 SrTi _1-yMn_yO₃ ceramics a decrease of the dielectric tunability, following a reduction of dielectric permittivity was observed.