Clear experimental evidence for phase transitions was shown in titanium doped lead magnesium niobate compositional disordered ferroelectric ceramics. One is the diffused phase transition around the temperature of diel...Clear experimental evidence for phase transitions was shown in titanium doped lead magnesium niobate compositional disordered ferroelectric ceramics. One is the diffused phase transition around the temperature of dielectric permittivity maxima, which is often assumed as the characteristics of relaxor ferroelectrics. Another is a first order transition from frequency dispersion relaxor ferroelectrics to normal ferroelectrics, corresponding to a zero field spontaneous polar micro macrodomain switching. According to the x ray diffraction, thermal analysis and transmission electron microscope results, it is pointed out that the relaxor state corresponds to a coexistence of cubic parent phase and nucleating rhombohedral ferroelectric microregion which is similar to a precursor martensite. After the spontaneous relaxor normal ferroelectrics transition, the lower symmetry phase is sure to be a long range rhombohedral phase. Thus a dynamic behavior of polar microregions is suggested to explain the phenomena, which is more similar to a stress induced martensitic transformations from cubical stabilized perovskite parent phase.展开更多
A new raw material was developed for the preparation of dense(K,Na)NbO_(3)(KNN)ceramics.In the absence of dopants,two kinds of KNN powder,calcined and microcrystalline powder,were used as matrix and seed to construct ...A new raw material was developed for the preparation of dense(K,Na)NbO_(3)(KNN)ceramics.In the absence of dopants,two kinds of KNN powder,calcined and microcrystalline powder,were used as matrix and seed to construct a duplex grain structure.The former was synthesized by the traditional solid phase reaction method and the latter by molten salt method.The effects of microcrystalline powder content on sintering behavior,microstructure and electric properties were investigated.It was found that appropriate microcrystalline powder content(x=0.4)promoted the grain growth and the gas diffusion,which resulted in a denser duplex grain structure and obtained a wide sintering temperature range.This work gives a basic raw material system for the development of high performance KNN ceramics.In addition,it also provides a new way to prepare dense ceramics by the design of a duplex structure.展开更多
Calcium bismuth niobate(CBN)ceramic,as a core element of high-temperature piezoelectric sensors,has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds.However,CB...Calcium bismuth niobate(CBN)ceramic,as a core element of high-temperature piezoelectric sensors,has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds.However,CBN usually faces two shortcomings.poor piezoelectric constant and low resistivity.In this work,CBN-based ceramics with donor–acceptor ions(W/Co)co-substituted at B-site were prepared by solid-state reaction method,and structure–property relationship of ceramics was studied in detail.Co-substitution of W/Co ions effectively improved the electrical property and hardness of CBN ceramics.CaBi_(2)Nb_(1.91)(W_(2/3)Co_(1/3)T_(0.09)O_(9))exhibits enhanced electrical and mechanical properties including high resistivity of-10^(7)Ω·cm at 500℃,piezoelectric constant of-15.3 pC/N and hardness value of-3.57 GPa.These values are two orders of magnitude,over two times,and 1.36 times higher than those of pure CBN ceramic,respectively.This work provides a reference for exploring other bismuth-layered structural ceramics.展开更多
Potassium–sodium niobate(K,Na)NbO3/(KNN)lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones.In recent years,the author’s group concentrated their work on KN...Potassium–sodium niobate(K,Na)NbO3/(KNN)lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones.In recent years,the author’s group concentrated their work on KNN-based ceramics.This paper reviews the main obtained results in authors’laboratory on how to enhance the piezoelectric properties of KNN-based ceramics,including the ions or compounds substitution,the constructing and types of phase boundaries near room temperature,the investigation of other tools(sintering aids,synthesis technique,poling conditions)on properties.All the published papers up to now show the developing higher performance with maintaining high Curie temperature of KNN-based ceramics which has great potential for the future and is the key to success for the field.展开更多
New lead-free piezoceramic nanocomposites of Boron Sodium Gadolinium Niobate(BNGN),with general formula(1-x)B_(0.5)Na_(0.5)GdO3xB_(0.5)Na_(0.5)NbO_(3),exhibiting a Morphotropic Phase Boundary(MPB),have been synthesiz...New lead-free piezoceramic nanocomposites of Boron Sodium Gadolinium Niobate(BNGN),with general formula(1-x)B_(0.5)Na_(0.5)GdO3xB_(0.5)Na_(0.5)NbO_(3),exhibiting a Morphotropic Phase Boundary(MPB),have been synthesized following hydrothermal method followed by solid state sintering.The occurrence of MPB at the composition with x=0.55,at which rhombohedral and monoclinic phases are found to coexist,has been confirmed using powder XRD.This accounts for the occurrence of large remnant polarization when the sintered ceramic pellets are subjected to electric poling at 2KV/mm.Uniform microstructure of various compositions is confirmed by SEM imaging.Dielectric and piezoelectric properties of the samples are found to be comparable to those of commercial grade PZT.At the MPB,the d_(33)coefficient is found to be 556 pC/N,which is close to that of commercial grade PZT,which makes BNGN a promising material to substitute lead containing PZT in the near future.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
The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)...The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)Y_(0.2)Er_(0.2)Yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming method.Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion.The high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room temperature.High-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal conductivity.There is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance test.The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.展开更多
文摘Clear experimental evidence for phase transitions was shown in titanium doped lead magnesium niobate compositional disordered ferroelectric ceramics. One is the diffused phase transition around the temperature of dielectric permittivity maxima, which is often assumed as the characteristics of relaxor ferroelectrics. Another is a first order transition from frequency dispersion relaxor ferroelectrics to normal ferroelectrics, corresponding to a zero field spontaneous polar micro macrodomain switching. According to the x ray diffraction, thermal analysis and transmission electron microscope results, it is pointed out that the relaxor state corresponds to a coexistence of cubic parent phase and nucleating rhombohedral ferroelectric microregion which is similar to a precursor martensite. After the spontaneous relaxor normal ferroelectrics transition, the lower symmetry phase is sure to be a long range rhombohedral phase. Thus a dynamic behavior of polar microregions is suggested to explain the phenomena, which is more similar to a stress induced martensitic transformations from cubical stabilized perovskite parent phase.
基金the National Natural Science Foundation of China(No.51502191)Fundamental Research Program of Shanxi Province(No.202103021224080)。
文摘A new raw material was developed for the preparation of dense(K,Na)NbO_(3)(KNN)ceramics.In the absence of dopants,two kinds of KNN powder,calcined and microcrystalline powder,were used as matrix and seed to construct a duplex grain structure.The former was synthesized by the traditional solid phase reaction method and the latter by molten salt method.The effects of microcrystalline powder content on sintering behavior,microstructure and electric properties were investigated.It was found that appropriate microcrystalline powder content(x=0.4)promoted the grain growth and the gas diffusion,which resulted in a denser duplex grain structure and obtained a wide sintering temperature range.This work gives a basic raw material system for the development of high performance KNN ceramics.In addition,it also provides a new way to prepare dense ceramics by the design of a duplex structure.
基金supported by the National Natural Science Foundation of China[51932010,12004267]Natural Science Foundation Project of Chongqing Science&Technology Commission[CSTB2024NSCQ-MSX2081]+3 种基金Scientific and Technological Research Program of Chongqing Municipal Education Commission[KJQN202401132]Open Project Fund of Key Laboratory of Inorganic Functional Materials and Devices,ChineseAcademy of Sciences[KLIFMD202311]Sichuan Science and Technology Program[23ZDYF0173]the Cultivation Project of CQUT for Research and Innovation Group.
文摘Calcium bismuth niobate(CBN)ceramic,as a core element of high-temperature piezoelectric sensors,has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds.However,CBN usually faces two shortcomings.poor piezoelectric constant and low resistivity.In this work,CBN-based ceramics with donor–acceptor ions(W/Co)co-substituted at B-site were prepared by solid-state reaction method,and structure–property relationship of ceramics was studied in detail.Co-substitution of W/Co ions effectively improved the electrical property and hardness of CBN ceramics.CaBi_(2)Nb_(1.91)(W_(2/3)Co_(1/3)T_(0.09)O_(9))exhibits enhanced electrical and mechanical properties including high resistivity of-10^(7)Ω·cm at 500℃,piezoelectric constant of-15.3 pC/N and hardness value of-3.57 GPa.These values are two orders of magnitude,over two times,and 1.36 times higher than those of pure CBN ceramic,respectively.This work provides a reference for exploring other bismuth-layered structural ceramics.
基金This work was supported by the National Natural Science Foundation of China(No.51332003).
文摘Potassium–sodium niobate(K,Na)NbO3/(KNN)lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones.In recent years,the author’s group concentrated their work on KNN-based ceramics.This paper reviews the main obtained results in authors’laboratory on how to enhance the piezoelectric properties of KNN-based ceramics,including the ions or compounds substitution,the constructing and types of phase boundaries near room temperature,the investigation of other tools(sintering aids,synthesis technique,poling conditions)on properties.All the published papers up to now show the developing higher performance with maintaining high Curie temperature of KNN-based ceramics which has great potential for the future and is the key to success for the field.
文摘New lead-free piezoceramic nanocomposites of Boron Sodium Gadolinium Niobate(BNGN),with general formula(1-x)B_(0.5)Na_(0.5)GdO3xB_(0.5)Na_(0.5)NbO_(3),exhibiting a Morphotropic Phase Boundary(MPB),have been synthesized following hydrothermal method followed by solid state sintering.The occurrence of MPB at the composition with x=0.55,at which rhombohedral and monoclinic phases are found to coexist,has been confirmed using powder XRD.This accounts for the occurrence of large remnant polarization when the sintered ceramic pellets are subjected to electric poling at 2KV/mm.Uniform microstructure of various compositions is confirmed by SEM imaging.Dielectric and piezoelectric properties of the samples are found to be comparable to those of commercial grade PZT.At the MPB,the d_(33)coefficient is found to be 556 pC/N,which is close to that of commercial grade PZT,which makes BNGN a promising material to substitute lead containing PZT in the near future.
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supported by the National Natural Science Foundation of China(No.52072301)the State Key Laboratory of Solidification Processing(NPU)(No.2021-TS-08)+3 种基金the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KFZD202102)the China-Poland International Collaboration Fund of National Natural Science Foundation of China(No.51961135301)the Fundamental Research Funds for the Central Universities(No.D5000210722)State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(No.P2020–009)。
文摘The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)Y_(0.2)Er_(0.2)Yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming method.Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion.The high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room temperature.High-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal conductivity.There is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance test.The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.
