SrLa(R0.5Ti0.5)O4 (R=Mg,Zn) microwave dielectric ceramics with complex K2NiF4‐type layered perovskite structure

Dense SrLa(R_0.5Ti_0.5)O₄ (R=Mg, Zn) ceramics were prepared by a standard solid‐state reaction method. The single phase with complex K₂NiF₄‐type layered perovskite structure and I4/mmm space group was revealed by XRD, and the refined structure was analyzed by Rietveld analysis. Significantly improved dielectric constant was obtained in SrLa(R_0.5Ti_0.5)O₄ ceramics compared to the analogues SrLaAlO₄ and SrLaGaO₄, which is attributed to the increasing normalized bond lengths of Sr/La‐O(1) and Sr/La‐O(2a) bonds and the higher polarizability of (R_0.5Ti_0.5)³⁺ than Al³⁺ and Ga³⁺. In addition, τ_f converts to a positive value with the increase in dielectric constant. The following microwave dielectric properties were obtained in the dense ceramics: ε_r=25.5, Qf=72 000 GHz, τ_f=29 ppm/°C for SrLa(Mg_0.5Ti_0.5)O₄, and ε_r=29.4, Qf=34 000 GHz, τ_f=38 ppm/°C for SrLa(Zn_0.5Ti_0.5)O_4. Furthermore, the stability of K₂NiF₄‐type structure in MLnBO₄ M=Ca, Sr, Ba; Ln=Y, Sm, Nd, La; B=Al, Ga, (Mg_0.5Ti_0.5), (Zn_0.5Ti_0.5)] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M²⁺ and Ln³⁺, based on which near‐zero τ_f values are expected to be obtained in SrLa(R_0.5Ti_0.5)O₄‐SrLaAlO₄ and SrLa(R_0.5Ti_0.5)O₄–SrLaGaO₄ unlimited solid solutions.