Microwave dielectric properties of temperature-stable (Mg_(0.95)Co_(0.05))_2TiO_4-Li_2TiO_3 composite ceramics for LTCC applications

摘要

In this paper, the effects of Li_2O-B_2O_3-Bi_2O_3-SiO_2 (LBBS) glass on the phase formation, sintering characteristic, the microstructure and microwave dielectric properties of temperature-stable (Mg_(0.95)Co_(0.05))_2TiO_4-Li_2TiO_3 ceramics were investigated. (Mg_(0.95)Co_(0.05))_2TiO_4-Li_2TiO_3 powders were obtained by using the traditional solid-state process. A small amount of LBBS doping can effectively reduce sintering temperature and promote the densification of the ceramics. X-ray diffraction analysis revealed not only the primary phase (Mg·Co)_2TiO_4 associated with Li_2TiO_3 minor phase but also a third phase (Mg·Co)TiO_3. The dielectric constant and Qf values vary with the doping amount of LBBS and sintering temperatures. With the compensation of the positive temperature coefficient (τ_f) of Li_2TiO_3 and the negative τ_f of (Mg_(0.95)Co_(0.05))_2TiO_4, the τ_f of the specimens fluctuates around zero. The (Mg_(0.95)Co_(0.05))_2TiO_4 ceramic with 2.5 wt% LBBS addition and sintering at 900 °C for 4 h exhibited excellent microwave dielectric properties: ɛ_r = 19.076, Qf = 126100 GHz, and τ_f = 0.98 ppm/°C.