Effects of composition on low temperature sinterable Ba–Nd–Sm–Ti–O microwave dielectric materials

This work investigated the effects of MgO and ZnO additives on the microwave properties of BRT114=[(BaO·R2O3·4TiO2)·0.06(2Bi2O3·3TiO2)] materials. Incorporation of small amount of ZnO (≦1 wt.%) markedly lowered the temperature coefficient of resonant frequency (τf), to around τf ≒1 ppm/°C, slightly increased the density and dielectric constant (εr) of the materials, but degraded the Q×f factor . Doping 2.5 mol% of MgO, in addition to ZnO, further improved the τf -value for the BRT114 materials. The dielectric constant and the Q×f factor of the materials degrade pronouncedly when doped with too abundant ZnO. Microstructure and EDX analyses indicated that the main factor for degrading the microwave properties is the induction on formation of secondary phases. Moreover, sol–gel and fused Ba–B–Si glass reacted with BRT114 in quite a different way. Fused glass wets BRT114 materials more easily than the sol–gel derived glass, resulting in composite materials with higher density and larger dielectric constant. Precalcining the glass-dielectrics mixture, greatly improved the wetting ability of the glass and markedly increased the microwave properties of the glass/dielectric composite, i.e. LTCC materials.