Effects of Al2O3 addition on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 ceramics

Ba4Nd9.33Ti18O54·x wt%Al2O3 (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al2O3 on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al2O3 additive gave rise to a second phase BaAl2Ti5O14 (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al2O3 additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180 GHz and decreased the τf value from 53.4 to 11.2 ppm/°C. A BNT-A ceramic with excellent dielectric properties: εr=70.2, Q×f=12,180 GHz, τf=20 ppm/°C was obtained with 2.0 wt% Al2O3 added after sintering at 1320 °C for 4 h.