Energy Storage Characteristics And Mechanism Of AgNbO₃-Based Lead-Free Antiferroelectric Ceramics

The demands for dielectric capacitors concentrate on miniaturization,lightweight,and integration and high energy-storage density for the rapid development of high-power electronic devices.Recently,Pb-based antiferroelectric materials,such as Pb?Zr,Ti?O₃,have been intensively investigated for high-performance energy storage applications.However,the use of lead may cause environmental problems,putting forward the necessity and urgency to investigate novel environment-friendly lead-free antiferroelectric system.AgNbO₃?abbreviated as:AN?,as a novel lead-free anti-ferroelectric material,is a promising candidate for energy storage applications owing to stable anti-ferroelectric characteristic and high Curie temperature(T_M3-O=353^oC),resulting into its unique advantages of high energy-storage density??2J/cm³?and good thermal stability.It is putted forward the necessity and urgency to discover develop novel dielectric materials with both high energy storage density and efficiency.To satisfy practical applications and the miniaturization of electronic devices,we successfully designed and fabricated a series of novel AgNbO₃energy storage materials.In chapter 3,the“aliovalent A-site engineering”,as a novel strategy,was proposed to develop AN-based ceramics with both decreasing tolerant factor?t?and enhancing antiferroelectricity.In our works,the divalent Alkaline earth elements,such as Ba²⁺,Sr²⁺and Ca²⁺,doping AN ceramics were successfully prepared,where variations of crystal structure and energy-storage performance were systematically investigated.Further investigations reveal that the incorporation of abovementioned aliovalent elements in Ag⁺-site can improve the antiferroelectricity of AN ceramics.As a result of enhancing antiferroelectricity and high breakdown strength??190 k V/cm?,the recoverable energy storage density can be largely tailored from 1.8 J/cm³for pure AN counterpart to 2.3 J/cm³,2.9 J/cm³and 3.55 J/cm³,respectively.Furthermore,due to slimmer P-E loops,this kind of ceramics realized high efficiency.Indeed,the doped materials exhibited good thermal stability.Therefore,the“aliovalent A-site engineering”is an effective strategy to achieve high energy storage performance for AN-based ceramics.In chapter 4,we successfully prepared the trivalent rare earth elements La³⁺and Sm³⁺doping AN ceramics to further enhance energy storage performance.Ultrahigh breakdown strength??240 k V/cm?was achieved in doped AN ceramics.Of particular importance is that ultrahigh recoverable energy storage density of 5.2 J/cm³with high energy efficiency of 69.2% was realized in Sm-doping AN ceramics.Indeed,the Sm-doping materials exhibited good thermal stability.Furthermore,Sm-modified AN ceramic also exhibited an ultrafast discharge speed??20?s?and high discharge energy density?4.2 J/cm³?.The abovementioned results indicate that the trivalent rare earth elements doping AN ceramics are promising materials for dielectric capacitors.In chapter 5,based on the aforementioned researches,the inner mechanism of enhancing antiferroelectric stability were further explored by taking Ag_1-3xSm_xNb_1-yTa_yO₃as examples,respectively.Of particular importance is that the inner structural/physical origins of improving antiferroelectricity were investigated,including cation displacement and octahedral rotation.