Ferroelectric and piezoelectric properties of non-stoichiometric Sr1−xBi2+2x/3Ta2O9 ceramics prepared from sol–gel derived powders

Ceramic compositions of strontium bismuth tantalate (SBT) [Sr1−xBi2+2x/3Ta2O9] with x = 0.0, 0.15, 0.30, 0.45 prepared from a sol–gel process have been studied. Stoichiometric and non-stoichiometric phases stable within the series have been investigated for their structural, dielectric, ferroelectric, and piezoelectric properties. Sintering at 1000 °C produces a single homogeneous phase up to x = 0.15. With x > 0.15 an undesirable BiTaO4 phase is detected and a higher sintering temperature (1100 °C) prevents the formation of this phase. The ferroelectric to paraelectric phase transition temperature (Tc) increases linearly from 325 to 455 °C up to x = 0.30, and with x > 0.30, it tends to deviate from the linear behavior. At x = 0.45 a broad and a weak transition is observed and the peak value of dielectric constant (ɛ′max) is significantly reduced. The piezoelectric coefficient (d33), remnant polarization (2Pr), and coercive field (2Ec) values increase linearly up to x = 0.30. The degradation in the electrical properties for x > 0.30 are attributed to the presence of undesirable BiTaO4 phase, which is difficult to identify by X-ray powder diffraction analysis (XRD) due to the close proximity of the peaks positions of BiTaO4 and the SBT phase.