The influence of doped MgF2 on the dielectric properties of barium strontium titanate ceramics

Barium-strontium titanate Ba1-xSrxTiO3 [0 <= x <= 1] has been investigated for tunable microwave application due to their high permittivity, low losses and high tunability. The influence of MgF2 additives on the dielectric performance of Ba0.6Sr0.4TiO3 (BSTO) were investigated in this paper. MgF2 doped BSTO ceramics were prepared using the conventional mixed oxide techniques. The phase structure, microstructure and dielectric properties of MgF2 doped BSTO ceramics were studied. The XRD patterns showed that all the samples exhibit a perovskite phase. A secondary phase of MgO was observed with excessive MgF2 additives. The grain size of MgF2 doped BSTO ceramics was slightly increased with the increasing of MgF2 additives, while the distributed porosity was concentrated to get larger. The relative permittivity, dielectric loss and tunability were decreased accordingly. The relative permittivity was reduced from 3717 (pure Ba0.6Sr0.4TiO3) to 680 (6 wt % MgF2 doped BSTO), while the tunability changed from 51.7 % to 6.5 %. The dielectric losses were decreased from 0.004 to less than 0.001. The Curie temperature of MgF2 doped BSTO was first decreased with the additives of MgF2 (x<2 wt %) then remain the same with the rise of MgF2 (2 <= x <= 6) content.