Abnormal variation of microwave dielectric properties in A/B site co-substituted (Ca_(1-0.3x)La_(0.2x))[(Mg_(1/3)Ta_(2/3))_(1-x)Ti_x]O_3 complex perovskite ceramics

摘要

A/B site co-substituted (Ca_(1-0.3x)La_(0.2x))[(Mg_(1/3)Ta_(2/3))_(1-x)Ti_x]O_3 ceramics (0.1 ≤ x ≤0.5) were prepared by solid state reaction and the structures, microstructures and dielectric properties were investigated. B site 1:2 cation ordering and oxygen octahedra tilting lead to monoclinic symmetry with spacegroup P2_1/c for x=0.1. For x above 0.1, the ordering was destroyed and the crystal structure became orthorhombic with space group Pbnm. The B site 1:2 cation ordering tended to be destroyed to form 1:1 ordering by the A site La~(3+) substitution. The dielectric constant increased linearly with increasing content of Ti~(4+) as the increasing second Jahn-Teller distortion enhanced the B site cation rattling. The temperature coefficient of resonant frequency and Qf values showed abnormal variations, which were refined to be caused by the increasing A site cation vacancy and diffused distribution of small size ordering domains respectively. Good combination of microwave dielectric properties was obtained at x = 0.5, where ε_r = 48, Qf= 21,000 GHz and τ_f = 2.2 ppm/°C.