Electromechanical characterization of 0.55Pb(Ni1∕3Nb2∕3)O3–0.45Pb(Zr0.3Ti0.7)O3 fibers with Pt core

Piezoelectric fibers of composition 0.55Pb(Ni1∕3Nb2∕3)O3–0.45Pb(Zr0.3Ti0.7)O3 were fabricated by extrusion of Pb(Nb,Ni)O3–Pb(Zr,Ti)O3 (PNN–PZT) powder around a platinum wire. Their properties are compared with the same bulk material properties. Fiber’s ceramic component exhibits a d31 of −145pC∕N and a lateral coupling factor of −0.22. The bulk material properties are much higher with a d31 of −404pC∕N and a lateral coupling factor of −0.38. The origin of this discrepancy was investigated by different means: microstructure (grain size and perovskite phase ratio), density, and polarization limitations. The polarization is the main limitation. Due to the radial electric field, a radial polarization gradient is obtained that limits the polarization on the outer edge. The calculation of the expected properties are then found to be k31=−0.28 (homogenization of the properties’ gradient). The remaining discrepancy is then assumed to be due to a density problem that can explain the 30% property loss. Density effect on piezoelectric properties of PNN-PZT bulk ceramics is presented to validate this assumption.