Ferroelectric-antiferroelectric Phase Transition Of Silver-based Lead-free Ceramics

The rapid development of electronic science and technology has been increasingthe requirements for functional materials,and dielectric materials?such as piezoelectric materials,energy storage materials?play an important role in the electronic information field.Lead-based materials are predominant in both the piezoelectrics and antiferroelectrics for energy storage applications due to their excellent properties.However,due to the toxicity and volatility of lead,it is urgent to investigate lead-free ceramic materials with comparable performance.Among the known lead-free ceramic materials,silver niobate?AgNbO₃?-based ceramics is a new type of lead-free dielectric material that has attracted much attention.It is promising in the piezoelectric and antiferroelectrics fields for researching and applications.AgNbO₃ is perovskite structure.and the stability of its ferroelectric and antiferroelectric phases is related to the tolerance factor t(t=?R_A+R_O?/?2?R_B+R_O?.The ferroelectric and antiferroelectric phase transitions can be achieved by adjusting the tolerance factor?t?.Based on this idea,in this work,Li⁺,Na⁺,K⁺doped and BiMnO₃ modified AgNbO₃ ceramics were synthesized by traditional solid phase method.The effects of the introduction of Li⁺,Na⁺,K⁺and BiMnO₃ on the microstructure,phase structure,FE-AFE of AgNbO₃ ceramics were investigated.The followings are the conclusions:1.(Ag_1-xLi_x)NbO₃ ceramics are single perovskite structures.With increasing Li⁺,the phase tructure translated to rhombohedral phase from orthogonal phase at room temperature, he grain size increased to 38?m from 27?m,and relative density increased from 96.5% o 98.5%for(Ag_1-x-x Li_x)NbO₃ ceramics.The grown grain is attributed to the activated attice caused by Li⁺replacing Ag⁺.At 150 kV/cm,the P_r of AgNbO₃ ceramics was 7.8 C/cm,while that of(Ag_0.92Li_0.08)NbO₃ ceramics was 24?C/cm.Meanwhile,E_A and E_F isappeared,indicating that the introduction of Li⁺could significantly enhance the erroelectric properties of AgNbO₃ ceramics.2.(Ag_1-xNa_x)NbO₃ ceramics are single perovskite structures with orthogonal phase at oom temperature.With the increase of Na⁺,the grain size increased from 23?m to 28?m,and the relative density was above 96%of(Ag_1-xNa_x)NbO₃ ceramics.The grown rain is attributed to the activated lattice caused by Na⁺replacing Ag⁺.The E_A and E_F of(Ag_0.95Na_0.05)NbO₃ ceramics increased from 50 kV/cm,105 kV/cm to 52 kV/cm and 125 V/cm,respectively.The P_r of(Ag_0.95Na_0.05)NbO₃ ceramics decreased from 8.1?C/cm to ?C/cm.Those results shown that the introduction of Na⁺could significantly enhance he anti-ferroelectric properties of AgNbO₃ ceramics.The enhancement of ntiferroelectric properties was caused by the reduction of tolerance factor caused by the ubstitution of small size Na⁺for large size Ag⁺.At 200 kV/cm,the W_rec was 2.2 J/cm³,and the?was 40%for(Ag_0.9Na_0.1)NbO₃ ceramics.3.(Ag_1-xK_x)NbO₃ ceramics are single perovskite structures.With increasing K⁺,the grain ize decreased from 35?m to 15?m,and the relative density was above 98%for Ag_1-xK_x)NbO₃ ceramics.When K⁺introduction increased to 10mol%,the E_A and E_F isappeared,and the P_r increased from 7.8?C/cm to 36?C/cm.Those results shown that he introduction of K⁺could significantly enhance the ferroelectric properties of gNbO₃ ceramics,which is caused by the increase of the tolerance factor caused by the arge size of K⁺replacing the small size of Ag⁺.4.AgNbO₃-xBiMnO₃ ceramics are single perovskite structure.With the increasing iMnO₃,the grain size increased from 15?m to 22?m,and the relative density was above 96%for AgNbO₃-xBiMnO₃ ceramics.The grown grain is attributed to the activated lattice by introduction of BiMnO₃.The dielectric constant was hardly affected by the introduction of BiMnO₃,and the dielectric loss is reduced from 6%to 2%for AgNbO₃ ceramics,which is caused by increased density.When x=0⁰.6 mol%,the P_max of AgNbO₃-xBiMnO₃ ceramics decreased from 37.5?C/cm to 32.5?C/cm,P_r decreased from 4.8?C/cm to 2.5?C/cm,and E_F and E_A were 110 kV/cm,50 kV/cm increased to 130 kV/cm and 70 kV/cm,respectively.The enhancement of antiferroelectric properties was caused by the reduction of tolerance factor caused by by the introduction of BiMnO₃.At the same time,the appearance of the M₂ phase may also be the reason for the enhanced antiferroelectric properties.At 150 kV/cm,the W_rec was raised 2.2 J/cm³,and the?was 54%for AgNbO₃-0.6BiMnO₃ ceramic.