Synthesis, structural characteristics and dielectric properties of a new K₂NiF₄-type phase Sr₂Mn_0.5Ti_0.5O₄

A new K₂NiF₄-type phase Sr₂Mn_0,5Ti_0,5O₄ have been synthesized by a sol–gel procedure and characterized by X-ray powder diffraction, thermogravimetric analysis and scanning electron microscopy. There are no oxide ion vacancies in these materials; oxidation states of manganese and titanium were estimated as +4. Rietveld profile analysis shows that the phase crystallizes with tetragonal unit cell in the space group I4/mmm. Substitution of Ti⁴⁺ for Mn⁴⁺ does not affect the distortion of coordination polyhedra (Mn,Ti)O₆ and SrO₉. The dielectric properties of the ceramic samples are caused by structural and charge characteristics, regular coordination polyhedra SrO₉ and lack of charge ordering, which can lead to significant permittivity. Increase of the dielectric constant at temperatures above 453 K is caused mainly by the grain boundary processes explained in terms of the Maxwell–Wagner polarization model. - Highlights: • The new complex oxide Sr₂Mn_0,5Ti_0,5O₄ was prepared. • The structures of the compound were analyzed by Rietveld refinement. • Distortions of SrO₉ and (Mn,Ti)O₆ polyhedra are not strong. • Dielectric properties are determined by regular structure and lack of charge ordering. • Permittivity increase under heat is associated with processes at the grain boundaries.