Research On Doping Modification Of K_0.5Na_0.5NbO₃-LiTaO₃ Lead-free Piezoelectric Ceramics

Piezoelectric ceramics are widely used in sensors,transformers,and transducers because of the ability to convert mechanical energy and electrical energy.However,the most widely used of these devices is lead zirconate titanate?PZT?-based system.The lead content of these devices can reach more than 60%,and the high toxicity of lead can cause great harm to the environment from the production to the destruction process.Therefore,it is necessary to develop a new lead-free piezoelectric ceramic material with excellent performance.Potassium sodium niobate?KNN?has the same perovskite structure as PZT.Therefore,KNN has received extensive attention as an environmentally friendly and potential piezoelectric material.Although KNN have excellent dielectric properties and high Curie temperatures,their piezoelectric properties are relatively low,which limits their application.In this dissertation,KNN were studied with the addition of new compositions,ion substitution,sintering aids,and so on,which are mainly divided into the following parts:In the first part:the effect of LiTaO₃ on the microstructure,grain morphology and electrical properties of KNN were studied.It was found that after adding the new component LiTaO₃,the ceramics were perovskite structures,and the orthorhombic phase gradually changed to the tetragonal phase and the electrical properties were improved.When 0.05mol%Li TaO3 was added and sintered at1000°C for 2h,the crystal structure was in the orthogonal-tetragonal two-phase coexistence state,the grain size was uniform,the pores were few,and the electrical properties were the best(d₃₃=224 pC/N,k_p=0.31,?_r=445,tan?=0.06,P_r=13.05?C/cm²,E_c=10.56 kV/cm).The second part is to study the influence of Sb₂O₃ on the microstructure,grain morphology and electrical properties of 0.95KNN-0.05LT piezoelectric ceramics.The ceramics are perovskite structures.However,if the content of Sb₂O₃ is more than 2 mol%,the second phase will appear.The addition of Sb element can improve the electrical properties of the ceramic,refine the grains and reduce the internal friction of the ceramic.However,the best sintering temperature increases.When the sintering temperature is 1060°C and x=0.01,the crystal grains are more uniform and the electrical properties are best(d₃₃=221 pC/N;Q_m=1654;k_p=0.32;?_r=481;tan?=0.09;P_r=17.26?C/cm²,E_c=25.34 kV/cm).The third part is adding MnO₂ as sintering aid to(K_0.5Na_0.5Li_0.05)(Nb_0.94Sb_0.01Ta_0.05)O₃,and study its sintering performance,microstructure,electrical properties.After MnO₂ was added,the ceramics became harder and the piezoelectric constant decreased.However,the stacking of crystal grains was tight,the dielectric loss decreased,the shape of the hysteresis loop was symmetrical,and the leakage current decreased.When the sintering temperature is 1060°C and x=0.02,the crystal grains are more uniform and the electrical properties are best:(d₃₃=200 pC/N;Q_m=4270;k_p=0.35;?_r=521;tan?=0.04;P_r=12.68?C/cm²,E_c=22.98 kV/cm).The fourth part is to add new component(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ in0.95KNN-0.05LT ceramics.Its effect on the sintering performance,microstructure and electrical properties of 0.95KNN-0.05LT were studied.After the addition of BCZT,the crystal structure changed from an orthorhombic phase to a tetragonal phase,all producing a heterophase.With the increase of BCZT,the electrical properties increase first and then decrease,the number of pores in the crystal increases,and the dielectric loss increases.When the sintering temperature is1140°C and x=0.01,the crystal grains are more uniform and the electrical properties are best:(d₃₃=235 pC/N;Q_m=2134;k_p=0.28;?_r=620;tan?=0.05;P_r=13.23?C/cm²,E_c=26.64 kV/cm).