SrLa(R0.5Ti0.5)O4 (R=Mg, Zn) microwave dielectric ceramics with complex K2NiF4-type layered perovskite structure
Dense SrLa( R 0.5 Ti 0.5 )O 4 ( R= Mg, Zn) ceramics were prepared by a standard solid-state reaction method. The single phase with complex K 2 NiF 4 -type layered perovskite structure and I 4/ 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 0.5 Ti 0.5 )O 4 ceramics compared to the analogues SrLaAlO 4 and SrLaGaO 4 , 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 0.5 Ti 0.5 ) 3+ than Al 3+ and Ga 3+ . 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 0.5 Ti 0.5 )O 4 , and ε r =29.4, Qf= 34 000 GHz, τ f = 38 ppm/°C for SrLa(Zn 0.5 Ti 0.5 )O 4. Furthermore, the stability of K 2 NiF 4 -type structure in MLnB O 4 [ M =Ca, Sr, Ba; Ln =Y, Sm, Nd, La; B= Al, Ga, (Mg 0.5 Ti 0.5 ), (Zn 0.5 Ti 0.5 )] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M 2+ and Ln 3+ , based on which near-zero τ f values are expected to be obtained in SrLa( R 0.5 Ti 0.5 )O 4 -SrLaAlO 4 and SrLa( R 0.5 Ti 0.5 )O 4 –SrLaGaO 4 unlimited solid solutions.
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