Modification of strain and piezoelectricity in (K,Na)NbO3-(Bi,Na)HfO3 lead-free ceramics with high Curie temperature

In this work, the (1-x)K0.45Na0.55NbO3-xBi0.5Na0.5HfO3 lead-free ceramics with a high Curie temperature were prepared by the normal sintering, and the enhancement in strain and piezoelectricity can be attained by tailoring the corresponding compositions. The orthorhombic-tetragonal (OT) phase coexistence was observed in the ceramics with 0.03 < x < 0.055, and then such a phase boundary was reasonably identified by X-ray diffraction patterns as well as temperature -dependent Raman spectra and dielectric constant. A large piezoelectric constant (d33) of ∼385 pC/N and a high Curie temperature (TC) of ∼315 °C can be simultaneously induced in the ceramics with x = 0.05. More interestingly, a high unipolar strain of ∼0.187% was shown in the ceramics with x = 0.04. It was found that the enhanced piezoelectric properties should be attributed to the two phase coexistence as well as enhanced dielectric and ferroelectric properties. We believe that this material is one of the most promising candidates in the field of high-temperature piezoelectrics.