2. Experimental
BNKFT x/0.03 and BNKFT y/0.18 were prepared by
the combustion technique. The starting materials used in
this study were Bi2O3, Na2CO3, K2CO3, TiO2 and Fe2O3.
Stoichiometric amounts of starting powders were weighed
and ball-milled using zirconia milling media for 24 h in
ethanol. The raw materials were well-mixed with the fuel
(glycine) in an agate mortar before calcination. The
powders were calcined at 750 1C for 2 h and were mixed
with polyvinyl alcohol; then it was pressed into discs with a
diameter of 15 mm under 80 MPa. These pellets were
subsequently sintered at 1000–1050 1C for 2 h.
Phase identifications of sintered ceramics were investigated
using an XRD. The microstructures of all ceramics
were observed using SEM. Dielectric properties were
measured at a temperature in the range of 25–450 1C with
a measured frequency of 1 kHz using a 4263B LCR-meter.
Ferroelectric hysteresis loop was obtained using a ferroelectric
test system. To obtain piezoelectric coefficient
(d33), the sintered pellets were polled under a DC field of
4 kV/mm at 120 1C in silicone oil for 30 min and measured
using a quasistatic d33 meter.