Dielectric and ferroelectric properties of (Bi0.5Na0.5)0.94-δBa0.06Ti1-xNbxO3 lead-free ceramics

Lead-free ceramics (Bi0.5Na0.5)(0.94-delta)Ba0.06Ti1-xNbxO3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were prepared via a solid-state sintering method. The ceramics exhibit pure perovskite structure as x <= 0.04, while the ceramic with x = 0.05 has a secondary phase. The rhombohedral (R)-tetragonal (T) morphotropic phase boundary exists in all the samples. The relative content of the T phase increases due to the Nb5+ doping. The ceramics show dense microstructures with mean grain sizes around 1-2 mu m. The changes of dielectric constant and dielectric loss as a function of temperature for the unpoled and poled samples were compared. Two dielectric anomalies appear on the dielectric curves around the temperatures denoted as T-RE and T-m. With the increase of Nb5+ amount, the values of T-RE decrease and T-m increase. The Nb5+-doped ceramics exhibit better temperature stability of dielectric constant during a wide high-temperature window. The polarization hysteresis (P-E) loops change from typical ferroelectric loops for the sample with x = 0 to constricted P-E loops with increasing Nb5+ amount. The ceramic with x = 0.03 shows a maximum strain (S-max) of 0.55% and piezoelectric strain constant (d(33)*) of 675 pm/V.