Lattice vibrational modulation of Ba0.5Sr0.5TiO3-CaAl4O7 composite ceramics and its effect on dielectric properties

(1- x )Ba 0.5 Sr 0.5 TiO 3 - x CaAl 4 O 7 composite ceramics were prepared by solid-phase reaction method. The effects of ion diffusion and composite effects on the microwave dielectric properties of composite ceramics are analyzed in detail. The results show that as the CaAl 4 O 7 content increases, the ion diffusion intensifies, resulting in the weakening of the lattice vibration intensity of the composite ceramics and the weakening of the anharmonic vibration of Ti 4+ . Thus, the Curie peak moves toward low temperature and the tunability of the composite ceramic decreases. In addition, the difference in the influence of monoclinic structure and spinel structure on the tunability of BST ceramics is related to the degree of inhibition of BST grain growth by the two. With the continuous increase of CaAl 4 O 7 content, the composite effects became prominent, which effectively reduced the dielectric permittivity and significantly increasing the Q value of the ceramic sample. When x  = 15 wt%, a composite ceramic with good microwave dielectric properties is obtained: ɛ r  = 298, Q = 294 (2.953 GHz), and the tunability is 12 % (20 kV/cm).