Low sintering temperature high permittivity ceramic composites for dielectric loaded microwave antennas

Compositions based on 0.2 Ca_0.8Sr_0.2TiO₃–0.8Li_0.5Sm_0.5TiO₃ (CST–LST), suitable for microwave applications were developed by adding BaCu (B₂O₅) additives and TiO₂ dopant in order to tune the microwave dielectric properties and lower sintering temperature. Addition of BaCu (B₂O₅) lowered the firing temperature about 300 °C. A single solid solution phase with perovskite structure was formed through the entire compositions with BaCu (B₂O₅). The CST–LST ceramics with 5 wt% BaCu (B₂O₅) sintered at 950 °C exhibited the microwave dielectric properties of ε_r = 66.7, Q × f = 3,222 GHz, τ _f  = −21.3 ppm/°C. Adding TiO₂ also improved the microwave properties. Typically, the CST–LST + 5 wt% BaCu (B₂O₅) + 1.5 wt% TiO₂ sintered at 950 °C showed ε_r = 71.6, Q × f = 3,441 GHz, τ _f  = −10.8 ppm/°C. The high permittivity and low firing temperatures of BaCu (B₂O₅) added CST–LST ceramics with TiO₂ dopant can be ideal for the development of low cost ultra-small dielectrically loaded antennas. Compatibility with Ag electrode indicated that this material was suitable for low temperature co-fired ceramics.