Residual Stress Effects on Fatigue of Piezoelectric-Electrostrictive Pb(Mg1/3,Nb2/3)O3-PbTiO3 Monolithic Bi-Layer Composite Actuators

The residual stress effects on fatigue of monolithic piezoelectric 0.65Pb(Mg_1/3,Nb_2/3)O₃-PbTiO₃-electrostrictive 0.90Pb(Mg_1/3,Nb_2/3)O₃-PbTiO₃ monolithic bi-layer composite structures were investigated by X-ray diffractometry. Fatigue measurements on bi-layers composite co-sintered at 1150 degC indicated a 30% increase in polarization after 10⁷ cycles for the 1:1 PE thickness ration bi-layers, which is attributed to self-poling due to a diffuse transition layer in the vicinity of the interface. It has been found that partial 90deg domain switching prior to poling is induced by the residual stresses imposed by thermal expansion mismatch between the electrostrictive and piezoelectric layers, as well as the spontaneous strain of the cubic-tetragonal transition in the ferroelectric layer itself. By X-ray diffractometry, an increase in the (002) peak intensity of the piezoelectric layer was observed, indicating a partial out-of-plane c-domain alignment, which most likely facilitates further alignment of such domains upon the application of a poling electric field, along with 180deg domains.