Enhancing Properties in Microwave Ceramics Using a Designer Sintering Aid

It has recently been shown that 0.2CaTiO3–0.8(Li0.5Nd0.5)TiO3 (CTLNT) with the addition of 4 wt% Bi4B2O9 (BBO) as a liquid‐phase sintering aid gives rise to exceptional microwave (MW) dielectric properties, (relative permittivity, εr = 125, quality factor, Qf0 and temperature coefficient of the resonant frequency, τf = 4 ppm/°C) at reduced sintering temperatures (1200°C). In this study, X‐ray diffraction and scanning and transmission electron microscopy have been used to elucidate the mechanism by which MW dielectric properties are optimized. It is demonstrated that highly polarizable Bi3+ ions enter the perovskite lattice thereby increasing εr. The concomitant ex‐solution of TiO2 as BBO concentration increases implies that ionic compensation occurs through the formation of VTi″″ in the perovskite lattice and infers that Bi3+ substitutes on the A‐site for lower valence ionic species according to the equation: 4AAx+TiTix⇒4BiA·+VTi″″. The residual boron rich material acts as a sintering aid with strongly −ve τf that compensates for the +ve τf of the perovskite matrix. This mechanism points to a new way of utilizing designer sintering aids in the development of microwave ceramics.