Synthesis and microwave dielectric properties of BaO-Sm2O3-5TiO2 ceramics with NdAlO3 additions

BaO-Sm2O3-5TiO2 (BST5) ceramics with NdAlO3 additions of up to 15 wt% were produced with a solid state reaction method, and their structural and microwave dielectric properties were determined. Experimental results showed that NdAlO3 neither merged nor altered the orthorhombic tungsten bronze structure of the main phase of the produced ceramics (except for a shrinkage in the crystal lattice), but it was segregated in distinct grains in the microstructure of the produced ceramics. However, the amount of NdAlO3 strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (εr) and the temperature coefficient of resonant frequency (τf) of the produced BLT5 ceramics can be tuned with the amount of NdAlO3 additions and the sintering process parameters. The best dielectric properties were achieved for BaO-Sm2O3-5TiO2 ceramics with 7.5% NdAlO3 (εr=73.22, Q×f =10,300 GHz, and τf=−1.05 ppm/°C).