Tuning dielectric properties in ceramics with anisotropic grain structure: The effect of sintering temperature on BaLa4Ti4O15

The orientation and grain aspect ratio, size and distribution of BaLa4Ti4O15 (BLT) ceramics have been studied as a function of sintering temperature with a view to elucidating a general principle by which the microwave properties (MW) can be understood/tuned in systems which exhibit anisotropic grain structures. For BLT sintered at 1500 °C, εr reaches a maximum of 51, with tan δ minimum at 0.002 and τεr = − 17 ppm/°C but εr subsequently varies non-linearly as sintering temperature increases. Since εr and τεr are directly proportional in the absence of a phase transition, the variation of τεr as a function of the sintering temperature is also nonlinear. This behaviour is related with variations in the orientation and grain aspect ratio, size and distribution with the sintering temperature and it is demonstrated that by controlling sintering conditions, microwave dielectric properties can be tuned. It is proposed that this is a general phenomenon which can also be used to explain the variation and tune the properties of other ceramic systems with anisotropic grain structures.