BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical...BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical properties.However,large leakage current limits their performance improvement and practical applications.In this work,direct current(DC)test,alternating current(AC)impedance,and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO_(3)–0.25BaTiO_(3)ceramics over a wide temperature range.In the range of room temperature(RT)−150℃,ohmic conduction plays a predominant effect,and the main carriers are p-type holes with the activation energy(Ea)of 0.51 eV.When T>200℃,the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity.The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry,oxygen vacancy concentration,and distribution,dominating internal conduction mechanism.Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO_(3)–BaTiO_(3)ceramics.展开更多
Over the past two decades,(K_(0.5)Na_(0.5))NbO_(3)(KNN)-based lead-free piezoelectric ceramics have made significant progress.However,attaining a high electrostrain with remarkable temperature stability and minimal hy...Over the past two decades,(K_(0.5)Na_(0.5))NbO_(3)(KNN)-based lead-free piezoelectric ceramics have made significant progress.However,attaining a high electrostrain with remarkable temperature stability and minimal hysteresis under low electric fields has remained a significant challenge.To address this long-standing issue,we have employed a collaborative approach that combines defect engineering,phase engineering,and relaxation engineering.The LKNNS-6BZH ceramic,when sintered at T_(sint)=1170℃,demonstrates an impressive electrostrain with a d_(33) value of 0.276%and 1379 pm·V^(-1)under 20 kV·cm^(-1),which is comparable to or even surpasses that of other lead-free and Pb(Zr,Ti)O_(3)ceramics.Importantly,the electrostrain performance of this ceramic remains stable up to a temperature of 125℃,with the lowest hysteresis observed at 9.73%under 40 kV·cm^(-1).These excellent overall performances are attributed to the presence of defect dipoles involving V′_(A)-V∙∙_(O) and B′_(Nb)-V∙∙O,the coexistence of R-O-T multiphase,and the tuning of the trade-off between long-range ordering and local heterogeneity.This work provides a lead-free alternative for piezoelectric actuators and a paradigm for designing piezoelectric materials with outstanding comprehensive performance under low electric fields.展开更多
BiFeO_(3)—BaTiO_(3)lead-free piezoelectric ceramics exhibit superior piezoelectric properties while preser-ving a high Curie temperature.However,given the inherent Gibbs free energy law of BiFeO_(3),the system is dif...BiFeO_(3)—BaTiO_(3)lead-free piezoelectric ceramics exhibit superior piezoelectric properties while preser-ving a high Curie temperature.However,given the inherent Gibbs free energy law of BiFeO_(3),the system is difficult to avoid heterogeneous phases such as Bi_(25)FeO_(39)and/or Bi_(2)Fe_(4)O_(9),which are accompanied by the volatilization of Bi^(3+)and the change of Fe^(3+),resulting in low insulating properties and high dielectric loss.These factors hinder the enhancement of polarizability and the overall performance at elevated temperatures and electric field conditions.The present study focuses on a highly leaky 0.75BiFeO_(3)–0.25BaTiO_(3)ceramic,in which the Fe content is deliberately designed to be both severely excessive and deficient,and is prepared using a one-step low-temperature sintering process.It is noteworthy that the structural stability and defect suppression,even in this challenging system,are achieved via the one-step low-temperature sintering.This samples exhibit a distinctive self-tuning property and an excellent stability over a wide compositional range.First-principles density func-tional theory calculations and XPS analysis have for the first time confirmed that suppressing oxygen vacancies and Fe^(3+)valence states can reduce the concentration and mobility of hole carriers,thereby effectively reducing leakage current,with the mechanism shifting from ohmic conduction to space-charge-limited conduction.Even under the extreme compositional conditions of x=±5 and a low sintering temperature,the piezoelectric coefficients d33 reach 132 pC/N and 110 pC/N,respectively.These are significantly higher than those of the most stoichiometric 0.75BiFeO_(3)–0.25BaTiO_(3)counter-parts,setting a new performance record.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52072028,52032007)National Key R&D Program of China(No.2022YFB3807400).
文摘BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical properties.However,large leakage current limits their performance improvement and practical applications.In this work,direct current(DC)test,alternating current(AC)impedance,and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO_(3)–0.25BaTiO_(3)ceramics over a wide temperature range.In the range of room temperature(RT)−150℃,ohmic conduction plays a predominant effect,and the main carriers are p-type holes with the activation energy(Ea)of 0.51 eV.When T>200℃,the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity.The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry,oxygen vacancy concentration,and distribution,dominating internal conduction mechanism.Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO_(3)–BaTiO_(3)ceramics.
基金This study was financially supported by the National Natural Science Foundation of China(Nos.52032007 and 52072028)the National Key R&D Program(No.2022YFB3807400)+1 种基金the Basic Science Center Project of National Natural Science Foundation of China(No.52388201)Tsinghua University-Toyota Research Center.
文摘Over the past two decades,(K_(0.5)Na_(0.5))NbO_(3)(KNN)-based lead-free piezoelectric ceramics have made significant progress.However,attaining a high electrostrain with remarkable temperature stability and minimal hysteresis under low electric fields has remained a significant challenge.To address this long-standing issue,we have employed a collaborative approach that combines defect engineering,phase engineering,and relaxation engineering.The LKNNS-6BZH ceramic,when sintered at T_(sint)=1170℃,demonstrates an impressive electrostrain with a d_(33) value of 0.276%and 1379 pm·V^(-1)under 20 kV·cm^(-1),which is comparable to or even surpasses that of other lead-free and Pb(Zr,Ti)O_(3)ceramics.Importantly,the electrostrain performance of this ceramic remains stable up to a temperature of 125℃,with the lowest hysteresis observed at 9.73%under 40 kV·cm^(-1).These excellent overall performances are attributed to the presence of defect dipoles involving V′_(A)-V∙∙_(O) and B′_(Nb)-V∙∙O,the coexistence of R-O-T multiphase,and the tuning of the trade-off between long-range ordering and local heterogeneity.This work provides a lead-free alternative for piezoelectric actuators and a paradigm for designing piezoelectric materials with outstanding comprehensive performance under low electric fields.
基金National Natural Science Foundation of China(52032007)the National Key Research and Development Program(2022YFB3807400)for the support of this research.
文摘BiFeO_(3)—BaTiO_(3)lead-free piezoelectric ceramics exhibit superior piezoelectric properties while preser-ving a high Curie temperature.However,given the inherent Gibbs free energy law of BiFeO_(3),the system is difficult to avoid heterogeneous phases such as Bi_(25)FeO_(39)and/or Bi_(2)Fe_(4)O_(9),which are accompanied by the volatilization of Bi^(3+)and the change of Fe^(3+),resulting in low insulating properties and high dielectric loss.These factors hinder the enhancement of polarizability and the overall performance at elevated temperatures and electric field conditions.The present study focuses on a highly leaky 0.75BiFeO_(3)–0.25BaTiO_(3)ceramic,in which the Fe content is deliberately designed to be both severely excessive and deficient,and is prepared using a one-step low-temperature sintering process.It is noteworthy that the structural stability and defect suppression,even in this challenging system,are achieved via the one-step low-temperature sintering.This samples exhibit a distinctive self-tuning property and an excellent stability over a wide compositional range.First-principles density func-tional theory calculations and XPS analysis have for the first time confirmed that suppressing oxygen vacancies and Fe^(3+)valence states can reduce the concentration and mobility of hole carriers,thereby effectively reducing leakage current,with the mechanism shifting from ohmic conduction to space-charge-limited conduction.Even under the extreme compositional conditions of x=±5 and a low sintering temperature,the piezoelectric coefficients d33 reach 132 pC/N and 110 pC/N,respectively.These are significantly higher than those of the most stoichiometric 0.75BiFeO_(3)–0.25BaTiO_(3)counter-parts,setting a new performance record.
