Study Of A/B Doping Effects On The Electrical Strain Of BNT Based Lead-Free Piezoelectric Ceramics

In this paper,the doped BNT piezoelectric ceramics have been obtained by traditional solid phase method and the effects of dopants on the phase structure,piezoelectric,dielectric,ferroelectric,and A/B doping effects on the electrical strain of BNT based lead-free piezoelectric ceramics were studied.The effect of Li ions substitution on phase structure,piezoelectric,dielectric,ferroelectricfor(Bi_1-xLi_x)_0.5(Na_0.84K_0.16)_0.5TiO₃?0.16BNKT-xLi?and(Bi_1-xLi_x)_0.5(Na_0.8K_0.2)_0.5TiO₃?0.2BNKT-xLi??x=0?0.01?0.02?0.04?was investigated.The XRD patterns confirmed the formation of pure perovskite structure,which indicated that the doping irons have been totally in the crystal lattice.The replacement for Li induced a phase transition from coexistence of ferroelectric tetragonal and rhombohedral phase to a pseudocubic phase in BNKT creramics.With increasing dopant content,the saturation polarization and remanent polarization of the material decrease while the coercive field increases slightly.This is because Li hasmadethematerial“hard”.For(Bi_1-xLi_x)_0.5(Na_0.84K_0.16)_0.5(Ti_1-xNb_x)O₃?0.16BNKT-xLiNb?while the Nb ions were doped into the B position in order to charge balance,there appeared similar phase transition.In 0.16BNKT-xLiNb ceramics,the largest electro-strain of 0.38%were achieved under an AEF of 5.5kV/mm at RT for x=0.05(d^*₃₃=S_max/E_max=690 pm/V).The effect of Sb and Al/Sb ions substitution on phase structure,piezoelectric,dielectric,ferroelectric for Bi_0.5(Na_0.84K_0.16)_0.5Ti_1-xSb_xO₃?0.16BNKT-xSb?and Bi_0.5(Na_0.84K_0.16)_0.5Ti_1-x(Al_0.5Sb_0.5)_xO₃?0.16BNKT-xAlSb?was investigated.The XRD patterns confirmed a phase transition to a pseudocubic phase.In P-E curves,Sb enhanced the diffuseness of ferroelectric-to-paraelectric phase transition and Al/Sb reducedtheferroelectricorderandinducedthetransitionfrom ferroelectric-to-relaxor.The effect of Al³⁺/Sb⁵⁺coping has the same effect compared with the Sb⁵⁺for the properties.At T_F-R,BNKT-x Sb exhibited larger strain up to0.30%@5.5 kV/mm(d^*₃₃=545 pm/V),and BNKT-xAlSb exhibited larger strain up to0.18%@5.5 kV/mm(d^*₃₃=327 pm/V).The effect of CuO substitution on phase structure,microstucture,dielectric,ferroelectric for BNT-BT-KNN.The XRD results showed coexistence of ferroelectric tetragonal and rhombohedral and lattice contraction after Cu addition.The liquid phase produced by CuO doping plays a role in the sintering process,reduce the sintering temperature to 950°C and T_F-R-R shift down from 70°C to RT.The field induced strain of the sample has been greatly improved after doping the highest properties with the strain of 0.37%@5kV/mm(d^*₃₃=740 pm/V).