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 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
behavior of BNT based ceramics and broad transition peaks are evident in
all samples. Dielectric constant up to 400 as well as acceptable low
dielectric loss at temperatures lower than 200 °C were obtained in BNT-BT
ceramics.