Effects of SrTiO3 additives on the structure and microwave dielectric properties of Ba4.2Sm9.2Ti18O54 ceramics

The effects of SrTiO3 additives on the microstructure and the dielectric properties of Ba4.2Sm9.2Ti18O54 (BST) materials have been investigated. The microstructure of BST doped with SrTiO3 was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The XRD, SEM and EPMA results showed that small amounts of SrTiO3 (less than 4 wt.%) could be accommodated in BST while a secondary metatitanate phase appeared in the samples with 8 wt.% SrTiO3 added, the addition of SrTiO3 increased the lower solubility limit (x values) of Ba6−3xSm8+2xTi18O54. The relative permittivities and the TCf values showed an approximately linear increase with increasing additions of SrTiO3. It was observed that near zero TCf values could be achieved with the addition of SrTiO3 to BST ceramics. With 4 wt.% SrTiO3 addition and sintered at 1360 °C for 2 h, BST ceramics exhibited excellent dielectric properties: ɛr = 81.2, Qf = 8470 GHz and TCf = −1.5 ppm/°C.