High electrostrain and the effects of relaxation degree on strain in poled BNT-based piezoelectric ceramics

Abstract

Bi0.5(Na0.82K0.18)0.5Ti1-x(Al0.5Ta0.5)xO3 (x = 0.01–0.06, BNKT-100xAT) lead-free piezoelectric ceramics are successfully prepared. The relaxation state of BNKT-100xAT ceramics is studied by selecting the representative samples based on its ferroelectric properties. BNKT-3AT and BNKT-5AT ceramics after polarization respectively have electrostrain of 0.54–0.8% and 0.41%–0.75% under 50–70 kV/cm, increasing about two times than that of unpoled state. The mechanism of strain enhancement, asymmetric phenomenon of P-E loops and S-E curves are discussed. Similar to the trend that the strain properties change with the relaxation degree in unpoled ceramics, the poled BNKT-4AT ceramics still have the highest strain response (S = 1.28%, 70 kV/cm). The frequency stability of BNKT-4AT ceramics is inferior, which is related to the PNRs content and the transformation of internal structure during the polarization process. Finally, it is found that BNKT-4AT ceramics have a unipolar strain value of 1.23% and d33* = 1750 pm/V under 70 kV/cm, exhibiting excellent electrostrain properties. In general, not only the piezoceramics with high electrostrain properties are successfully prepared, but also the effects of relaxation degree on the strain response of poled ceramics are analysed in this work. It also supplies significant reference for the requirement of relaxation degree to obtain high electrostrain in the piezoceramics design.