Dielectric and ferroelectric properties of (Bi 0.5 Na 0.5 ) 0.94-δ Ba 0.06 Ti 1−x Nb x O 3 lead-free ceramics

Lead-free ceramics (Bi0.5Na0.5)0.94-δBa0.06Ti1−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 μm. 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 TRE and Tm. With the increase of Nb5+ amount, the values of TRE decrease and Tm 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 (Smax) of 0.55% and piezoelectric strain constant (d33*) of 675 pm/V.