Phases, microstructure and microwave dielectric properties of hexagonal perovskite Ca(La1−xNdx)4Ti4O15 ceramics

Hexagonal perovskite microwave ceramics of Ca(La1−xNdx)4Ti4O15 with x changing from 0 to 0.5 were prepared by solid-state reaction method. The phase relationship, microstructure and microwave dielectric properties were investigated. The substitution of Nd for La has marked effect on the phases. For x = 0 and x = 0.125, the hexagonal perovskite phase remained in sintered ceramics. With x increasing further, a secondary phase with orthorhombic perovskite, Ca(La1−xNdx)4Ti5O17, was formed. The lattice parameters of hexagonal perovskite cell decrease linearly with increasing Nd content. The dielectric constant of sintered ceramics decreases from 43.61 to 42.30, the Q × f value from 33856 to 15207 GHz with x from 0 to 0.50. The τf value decreases from −17.1 ppm/°C for x = 0 to −5.77 ppm/°C for x = 0.50. The mechanisms responsible for the change of dielectric properties with the substitution of Nd for La in perovskite and with the sintering temperature were also investigated.