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

Dense SrLa(R0.5Ti0.5)O-4 (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(R0.5Ti0.5)O-4 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 (R0.5Ti0.5)(3+) than Al3+ and Ga3+. In addition, (f) converts to a positive value with the increase in dielectric constant. The following microwave dielectric properties were obtained in the dense ceramics: epsilon(r)=25.5, Qf=72 000 GHz, (f)=29 ppm/degrees C for SrLa(Mg0.5Ti0.5)O-4, and epsilon(r)=29.4, Qf=34 000 GHz, (f)=38 ppm/degrees C for SrLa(Zn0.5Ti0.5)O-4. Furthermore, the stability of K2NiF4-type structure in MLnBO(4) [M=Ca, Sr, Ba; Ln=Y, Sm, Nd, La; B=Al, Ga, (Mg0.5Ti0.5), (Zn0.5Ti0.5)] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M2+ and Ln(3+), based on which near-zero (f) values are expected to be obtained in SrLa(R0.5Ti0.5)O-4-SrLaAlO4 and SrLa(R0.5Ti0.5)O-4-SrLaGaO4 unlimited solid solutions.