Structure and dielectric properties of (1-x)Bi0.5Na0.5TiO3-xBaTiO3 piezoceramics prepared using hydrothermally synthesized powders.

The influence of different processing parameters and various Ba2+ addition (up to 10 mol%) on the structure and dielectric properties of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) ceramics was investigated. The powders were hydrothermally synthesized in the alkaline environment at 180°C for different time periods. X-ray diffraction confirmed the presence of dominant rhombohedral Bi0.5Na0.5TiO3 phase and a small amount of secondary pyrochlore Bi2Ti2O7 phase in the pure BNT powders. In addition, one-dimensional Na2Ti2O7 structure was also observed in the powder hydrothermally treated for a long time (i.e. 48 h). The amount of secondary pyrochlore phase in the BNT-BT powders increases with the increase of Ba2+ content. The synthesized powders were pressed into pellets and finally sintered at various temperatures up to 1150°C. High density (more than 90%TD) was obtained in all BNT-BT sintered samples. Optimal sintering parameters were chosen in order to obtain dense ceramics with the optimal phase composition. The temperature dependence of dielectric properties for the BNT-BT ceramics was also studied. Relaxor behaviour of BNT-based ceramics and broad transition peaks are evident in all samples. Dielectric constant up to 400 as well as an acceptable low dielectric loss at temperatures lower than 200°C were obtained in BNT-BT ceramics.