Stability and microwave dielectric characteristics of (Ca1-xSrx)LaAlO4 ceramics

The stability of K2NiF4 structure in MRAlO4 (M= Sr and Ca; R==La, Nd, Sm, and Y) ceramics was discussed via calculating the relative difference between the tolerance factors for ABCO(4) and ABO(3) structure, and the K2NiF4 structure became unstable when the above difference was greater than 4.3%. Among the above ceramics, CaLaAlO4 and SrYAlO4 were not stable. To improve the stability of K2NiF4 structure in CaLaAlO4, the effects of Sr substitution for Ca were investigated. The stability of K2NiF4 structure in (Ca1-xSrx)LaAlO4 ceramics increased with increasing x, and it became stable when x>0.9. Good microwave dielectric properties were achieved in (Ca0.05Sr0.95)LaAlO4 ceramics: epsilon=16.7, Q.f=28,171 GHz, tau(f)=-52.4 ppm/degrees C.