Study Of Doping Effects On The Properties Of Perovskite Lead-free Piezoelectric Ceramics

Piezoelectric ceramics are widely used in actuators,sensors and resonators.For environmental consideration,it is urgent to develop high performance lead-free piezoelectric ceramics.In this paper,the doped KNN and BNT piezoelectric ceramics have been obtained by conventional ceramics sintering technique and the effects of dopants on the phase structure,piezoelectric,dielectric,ferroelectric,and electric-field-induced strain properties were studied.Taking K_0.48Na_0.52NbO₃ as the substrate composition,the KNN-1000xLa and KNN-1000xLC ceramics were prepared by doping with La and Cu.The XRD patterns confirmed the formation of pure perovskite structure,which indicated that the La and Cu have been totally in the crystal lattice.The La addition enhanced the diffuseness of ferroelectric-to-relaxor transition and Cu addition helped to raise the E_c of the ceramics.The KNN-4La and KNN-9LC samples exhibited the highest properties with the strain of 0.09%@5 kV/mm and 0.11%@5 kV/mm,respectively.In this work,by doping Li,La and Nb,the BNBKT-100xLi?BNBKT-10000xLN andBNBKLT-10000xLNceramicswereobtainedwith0.85Bi_0.5Na_0.5TiO₃-0.11Bi_0.5K_0.5Ti O₃-0.04BaTiO₃ as the substrate composition.The XRD patterns exhibited the formation of pure perovskite structure,without a second phase.With the content of the addition increasing,the phase structure changed from the tetragonal and rhombohedral structure coexistence to pseudo-cubic structure at RT for all ceramics.It was found that the Li addition enhanced the diffuseness of ferroelectric-to-relaxor transition,and made the T_F-R shift down from 160°C to RT.The BNBKT-15Li exhibited larger strain up to 0.37%@6.5 kV/mm(d^*₃₃=570 pm/V).The similar phenomenon can be observed in the other two systems.The actuating performance of BNT-BKT-BT ceramics could be enhanced with proper amount of ion addition.BNBKT-75LN and BNBKLT-50LN ceramics showed the best electric-field-induced strain property at RT,while the strain is 0.39%@6 kV/mm(d^*₃₃=650 pm/V)and 0.36%@6 kV/mm(d^*₃₃=600 pm/V),respectively.The temperature stability of the electric-field-induced strain for all BNT-BKT-BT ceramics showed that the maximum values of S_max/E_max could be obtained when the temperature was near the T_F-R,indicating that the relaxor-to-ferroelectric transition contributes to the enhanced properties.The transition is sensitive to several conditions,including composition,temperature and applied electric field.