Effect Of A/B Site Doping On The Electro-Strain Of Ternary BNT-Based Lead-Free Piezoelectric Ceramics

Piezoelectric ceramics have been utilized in various electronic components,owing to their unique electromechanical conversion properties.The lead-based piezoelectric ceramics with prominent properties are widely used.However,due to the toxicity and hazards of lead element for environment and humans,it is imperative to find environment-friendly lead-free piezoelectric ceramics with excellent properties.In this paper,Bi_0.5Na_0.5TiO₃（BNT）based lead-free ceramics were used as the matrix to improve the electrical properties of ceramics by the means of A/B site doping ions and optimizing the preparation process.A-site Li⁺-doped 0.86(Bi_0.5(Na_1-xLi_x)_0.5)TiO₃-0.11(Bi_0.5K_0.5)TiO₃-0.03Ba TiO₃（x=0.025,0.050,0.075）ceramics were prepared by the solid-state reaction method.With the increase of Li⁺doping,the ferroelectric order gradually decreases.The unipolar electro-strain reaches to 0.33%@6 k V/mm at room temperature(d^*₃₃=550 pm/V).Meanwhile,when the Li⁺content is 0.050,the unipolar electro-strain can reach0.42%@5 k V/mm at 60℃(d^*₃₃=840 pm/V).In addition,the temperature stability increases with the increase of Li⁺doping.Similar results are obtained by the doping La³⁺on the same matrix.<001>textured A-site Li⁺-doped 0.852Bi_0.5Na_0.5TiO₃-0.11Bi_0.5K_0.5TiO₃-0.038Ba TiO₃ ceramics were prepared by the reactive templates grain growth（Reactive templated grain growth,RTGG）method,with a high orientation degree of 78%along the<001>direction.Outstanding electro-strain response is achieved due to the contribution of oriented-grains along the<001>direction.A large electro-strain of 0.55%with a relatively low hysteresis is obtained at 6.5 k V/mm with corresponding d^*₃₃ of846 pm/V in the textured ceramics,which is 49%higher than that of the random ceramics.Besides,the electro-strain can reach as high as 0.52%@5.5 k V/mm(d^*₃₃=945 pm/V)at 100°C.These results indicate that the RTGG is an effective way to design high performance lead-free piezoelectric materials.B-site Cu²⁺-doped（0.94-x）Bi_0.5Na_0.5TiO₃-0.06Ba TiO₃-x K_0.5Na_0.5Nb O₃-y Cu O（（0.94-x）BNT-0.06BT-x KNN-y Cu）ceramics were prepared by the solid-state reaction method.With the increase of KNN content,the ceramics will change from ferroelectric phase to ergodic relaxor state,while with a certain KNN content（x=0.03,0.01）,the addition of 0.01 mol.Cu²⁺will improve the electro-strain.Different types of defect dipoles in the aged samples will generate pinched phenomenon on the P-E loops of ferroelectric ceramics,and increase the electro-strain of ceramics.When x=0.03 and y=0.01,the best performance can be achieved after aging.The high unipolar electro-strain is 0.32%@6 k V/mm,and the corresponding d^*₃₃ is 533 pm/V.