Water-Induced Degradation in Lead Zinc Niobate--Lead Zirconate Titanate Soft Piezoelectric Ceramics

Water-induced degradation of lead zinc niobate--lead zirconate titanate (Pb(Zn_1/3Nb_2/3)O₃-Pb(ZrTi)O₃) soft piezoelectric ceramics is studied using electrochemical hydrogen charging, in which the silver electrodes of the piezoelectric ceramics constitute a cathode in 0.01-M NaOH solution to evolve hydrogen by electrolysis of water. It is found that with the increasing hydrogen charging time, the resonance impedance increases, the difference between the resonance frequency and the anti-resonance frequency decreases, the spontaneous polarization, the remanent polarization and the piezoelectric coefficient d₃₃ decrease. The degradation behaviour of the soft piezoelectric ceramics can be explained to hydrogen incorporating into the lattice and forming hydroxy (OH^-) bonds in the perovskite structure, which prevents the Ti ions from switching and increases the coercive field E_c. The degradation characteristics of the soft piezoelectric ceramics are quite different from that of lead zirconate titanate hard piezoelectric ceramics.