Structure Evolution and Enhanced Microwave Dielectric Characteristics of (Sr _{1− <i>x</i>} Ca _<i>x</i> )La ₂ Al ₂ O ₇ Ceramics

( Sr 1− x Ca x ) La 2 Al 2 O 7 (0.1 ≤ x ≤ 0.5) ceramics were prepared by a standard solid‐state reaction method. Their densification behavior and microwave dielectric properties were investigated together with the structural evolution. X‐ray diffraction analysis indicated that the major phase of Ruddlesden–Popper structure with n = 2 was obtained for all the compositions investigated here. Partial Ca substitution improved the sintering behavior of SrLa 2 Al 2 O 7 ceramics. More importantly, microwave dielectric characteristics were enhanced in ( Sr 1− x Ca x ) La 2 Al 2 O 7 ceramics with compositions of x = 0.1~0.3. The stacking fault was confirmed by TEM observation in the present ceramics, and the microwave dielectric loss was influenced by it. The best combination of microwave dielectric characteristics was achieved for the composition of x = 0.1: ε r = 19.9, Qf = 135 400 GHz and τ f = −18.5 ppm/°C.

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