The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase st...The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140℃and poling time of 20-25 min.展开更多
(1-x)(K(0.495)Na(0.495)La(0.01))(Nb(0.997)Cu(0.0075))O3-xBi(Mg(0.5)Zr(0.5))O3(abbreviated as KNLNC-xBMZ) ceramics were designed and prepared.The phase transition,microstructure and electrical properties of the ceramic...(1-x)(K(0.495)Na(0.495)La(0.01))(Nb(0.997)Cu(0.0075))O3-xBi(Mg(0.5)Zr(0.5))O3(abbreviated as KNLNC-xBMZ) ceramics were designed and prepared.The phase transition,microstructure and electrical properties of the ceramics were investigated.The phase structures of the ceramics transform from orthorhombic to pseudocubic phases and the grain sizes decrease gradually with BMZ content(x) increasing.Additionally,BMZ additions can significantly enhance the dielectric temperature stability and decrease the dielectric loss of ceramics over a relatively broad temperature range.KNLNC-0.02 BMZ ceramics exhibit high dielectric permittivity(εr=1542) and small variation(Δεr/ε(r150℃)≤±15%)in dielectric permittivity from 100 to 375℃,and low dielectric loss(tanδ≤2%) in the temperature range of 100-350℃,which suggests that this ceramic is a candidate for high-temperature capacitor application.展开更多
Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ...Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ℃ and dwell time for 2 h.The samples were characterized by X-ray diffraction and scanning electron microscopy,respectively.The dielectric properties of the 0.98KNN-0.02 LF ceramics were also investigated.The results show that all the ceramics sintered at different sintering temperatures are a pure pseudo-cubic perovskite phase,and it is effective to improve the density and dielectric properties when the sintering temperature increases.However,the properties of the ceramics can be deteriorated when the sintering temperature exceeds the optimum value.The 0.98KNN-0.02 LF ceramics sintered at1150 ℃ for 2 h show the optimum dielectric properties,i.e.,the high dielectric permittivity(near 2000) and low dielectric loss(<5%) in the temperature range of 100-400 ℃ and the capacitance variation(AC/C_(150℃)) of ±15%,indicating a potential application in high-temperature ceramics capacitors.展开更多
Through an analysis of the temperature stability of(K0.5Na0.5)NbO3(KNN)based ceramics and KNN solid solutions,we propose a method to enhance the temperature stability of KNN materials.These materials are valuable for ...Through an analysis of the temperature stability of(K0.5Na0.5)NbO3(KNN)based ceramics and KNN solid solutions,we propose a method to enhance the temperature stability of KNN materials.These materials are valuable for their piezoelectric properties.To verify the feasibility of this method,0.9(K1-xNax)NbO3-0.06LiNbO3-0.04CaTiO3(KNLN-CaTiO3)ceramics were designed,and their structure and properties were studied.The results show that KNLN-CaTiO3(x=0.54)ceramics have a good temperature stability over a wide temperature range(25-320°C).Also,they have good piezoelectric properties(d33=152 pC/N in x=0.54).This result confirms the feasibility of our proposed solution for improving the piezoelectric properties of KNN-based ceramics that have poor temperature stability.展开更多
The effects of dwell time on the phase structure, microstructure, and electrical properties were investigated for the 0.98（K0.sNa0.5）NbO3-0.02LaFeO3 ceramics （abbreviated as 0.98KNN-0.02LF）. All the ceramics sinte...The effects of dwell time on the phase structure, microstructure, and electrical properties were investigated for the 0.98（K0.sNa0.5）NbO3-0.02LaFeO3 ceramics （abbreviated as 0.98KNN-0.02LF）. All the ceramics sintered for different dwell time are of pure phase and the peak intensity of the 0.98KNN-0.02LF ceramics becomes stronger with a longer dwell time. Denser microstructures with larger grain size are developed for the sample with a longer dwell time. The maximum dielectric permittivity decreases with increasing the dwell time, and the deteriorative dielectric properties are due to the increasing grain size and the domain wall motion. Ferroelectric properties results indicate that 2Pr value slightly decreases with increasing the dwell time, while the 2Ec value increases. Consequently, the 0.98KNN-0.02LF ceramic sintered at 1150 ℃ for 2 h shows optimum dielectric properties （er=2253 and tan fi〈5%） and ferroelectric properties （2Pr=34.51 gC/cm2 and 2Ec=5.07 kV/mm）.展开更多
Potassium sodium niobate （KNN） powders were synthesized by a modified sol-gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating ag...Potassium sodium niobate （KNN） powders were synthesized by a modified sol-gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating agents, respectively, ethylene glycol （EG） and ethylene diamine tetraacetic acid （EDTA）/citrate. The effects of citric acid （CA）, EG, and EDTA on the stability of the precursor sol were systemically inves-tigated. The powders and gels were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis-differential scanning calorimetry （TGA-DSC）. The results indicated that a stable precursor sol was formed when n（CA）：n（Mn＋）= 3：1, n（EDTA）：n（NH4OH） = 1：3.5, and n（CA）：n（EG） = 1：2. The xerogel was calcined at 500-950 ℃ to prepare the KNN powder. Pure KNN perovskite phase with a cube-like structure was synthesized at 850 ℃ from the precursor sol for a K/Na molar ratio of 1.2. The formation mechanism of the KNN perovskite phase was also discussed.展开更多
The lead-free piezoelectric ceramics (1-x)(K0.5Na0.5)NbO3-xLiNbO3(abbreviated as KNLN) were synthesized by a traditional solid state reaction. The effects of Li+ on the sintering characteristic, the phase structure an...The lead-free piezoelectric ceramics (1-x)(K0.5Na0.5)NbO3-xLiNbO3(abbreviated as KNLN) were synthesized by a traditional solid state reaction. The effects of Li+ on the sintering characteristic, the phase structure and piezoelectric properties of KNLN ceramics were investigated. The sintering temperature of KNN-based ceramics is decreased by doping Li+ and the range of the sintering temperature is narrow. The KNLN ceramics exhibit an enhanced piezoelectric properties with the piezoelectric constant d33 value of 180-200 pC/N, The electromechanical coupling coefficients kp is 35%-40%. The results show that (1-x)(K0.5Na0.5)-NbO3-xLiNbO3 (x=0.05, 0.06) is a promising high-temperature lead free piezoelectric ceramic.展开更多
The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The ...The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The results reveale that the piezoelectricity stems from strong hybridization between the Nb atom and the O atom.At the same time,the K or Na atoms are replaced by the La doping atoms,which brings about the anisotropic relaxation.The La doping reduces the forbidden band,at the same time it makes Fermi surfaces shift toward the energetic conduction band(CB)of KNN.With the increase of La-doping intent,the phase structure of KNN extends from O-phase to T-phase and improves the piezoelectric properties of KNN.展开更多
基金Project(10474077) supported by the National Natural Science Foundation of China Project(2002CB613304) supported by the National Basic Research Program of China
文摘The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140℃and poling time of 20-25 min.
基金Doctorate Foundation of Northwestern Polytechnical University(CX201108)National Natural Science Foundation of China(51072165)State Key Laboratory of Solidification Processing in NWPU(KP200901)
基金financially supported by the National Natural Science Foundation of China(No.21501007)the Industrial Science and Technology Plan in Shaanxi Province of China (No.2016GY-226)+1 种基金the Doctoral Scientific Research Starting Foundation of Baoji University of Arts and Sciences (No.ZK15044)the Undergraduate Training Programs for Innovation and Entrepreneurship (No.201610721039)
文摘(1-x)(K(0.495)Na(0.495)La(0.01))(Nb(0.997)Cu(0.0075))O3-xBi(Mg(0.5)Zr(0.5))O3(abbreviated as KNLNC-xBMZ) ceramics were designed and prepared.The phase transition,microstructure and electrical properties of the ceramics were investigated.The phase structures of the ceramics transform from orthorhombic to pseudocubic phases and the grain sizes decrease gradually with BMZ content(x) increasing.Additionally,BMZ additions can significantly enhance the dielectric temperature stability and decrease the dielectric loss of ceramics over a relatively broad temperature range.KNLNC-0.02 BMZ ceramics exhibit high dielectric permittivity(εr=1542) and small variation(Δεr/ε(r150℃)≤±15%)in dielectric permittivity from 100 to 375℃,and low dielectric loss(tanδ≤2%) in the temperature range of 100-350℃,which suggests that this ceramic is a candidate for high-temperature capacitor application.
基金supported by the National Natural Science Foundation of China(51072165)the fund of State Key Laboratory of Solidification Processing in NWPU(KP201307)+1 种基金Doctor Start fund of Baoji University of Arts.&Sci.(ZK15044)the fund of Shaanxi Key Laboratory of Phytochemistry(13JS006)
文摘Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ℃ and dwell time for 2 h.The samples were characterized by X-ray diffraction and scanning electron microscopy,respectively.The dielectric properties of the 0.98KNN-0.02 LF ceramics were also investigated.The results show that all the ceramics sintered at different sintering temperatures are a pure pseudo-cubic perovskite phase,and it is effective to improve the density and dielectric properties when the sintering temperature increases.However,the properties of the ceramics can be deteriorated when the sintering temperature exceeds the optimum value.The 0.98KNN-0.02 LF ceramics sintered at1150 ℃ for 2 h show the optimum dielectric properties,i.e.,the high dielectric permittivity(near 2000) and low dielectric loss(<5%) in the temperature range of 100-400 ℃ and the capacitance variation(AC/C_(150℃)) of ±15%,indicating a potential application in high-temperature ceramics capacitors.
基金supported by the National Natural Science Foundation of China(10804130,60871027)the Shaanxi Provincial Natural Science Foundation(2009JQ1001)the Key Laboratory of Electrical Insulation and Power Equipment(EIPE10202)
文摘Through an analysis of the temperature stability of(K0.5Na0.5)NbO3(KNN)based ceramics and KNN solid solutions,we propose a method to enhance the temperature stability of KNN materials.These materials are valuable for their piezoelectric properties.To verify the feasibility of this method,0.9(K1-xNax)NbO3-0.06LiNbO3-0.04CaTiO3(KNLN-CaTiO3)ceramics were designed,and their structure and properties were studied.The results show that KNLN-CaTiO3(x=0.54)ceramics have a good temperature stability over a wide temperature range(25-320°C).Also,they have good piezoelectric properties(d33=152 pC/N in x=0.54).This result confirms the feasibility of our proposed solution for improving the piezoelectric properties of KNN-based ceramics that have poor temperature stability.
基金Project(CX201108)supported by the Doctorate Foundation of Northwestern Polytechnical University,ChinaProject(51072165)supported by the National Natural Science Foundation of ChinaProjects(KP200901,SKLSP201104)supported by the Fund of State Key Laboratory of Solidification Processing in NWPU,China
文摘The effects of dwell time on the phase structure, microstructure, and electrical properties were investigated for the 0.98（K0.sNa0.5）NbO3-0.02LaFeO3 ceramics （abbreviated as 0.98KNN-0.02LF）. All the ceramics sintered for different dwell time are of pure phase and the peak intensity of the 0.98KNN-0.02LF ceramics becomes stronger with a longer dwell time. Denser microstructures with larger grain size are developed for the sample with a longer dwell time. The maximum dielectric permittivity decreases with increasing the dwell time, and the deteriorative dielectric properties are due to the increasing grain size and the domain wall motion. Ferroelectric properties results indicate that 2Pr value slightly decreases with increasing the dwell time, while the 2Ec value increases. Consequently, the 0.98KNN-0.02LF ceramic sintered at 1150 ℃ for 2 h shows optimum dielectric properties （er=2253 and tan fi〈5%） and ferroelectric properties （2Pr=34.51 gC/cm2 and 2Ec=5.07 kV/mm）.
基金supported by the National Natural Science Foundation of China(NSFC No.51172108)Program for Changjiang Scholars and Innovative Research Teams in Universities(IRT0968)+2 种基金Program for New Century Excellent Talents in Universities(NCET10-0070)a project funded by the Priority Academic Program Development of Jiangsu Higher Education InstitutionsNanjing University of Aeronautics and Astronautics Research Fund for Fundamental Research(NJ2010010,NZ2010001)
文摘Potassium sodium niobate （KNN） powders were synthesized by a modified sol-gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating agents, respectively, ethylene glycol （EG） and ethylene diamine tetraacetic acid （EDTA）/citrate. The effects of citric acid （CA）, EG, and EDTA on the stability of the precursor sol were systemically inves-tigated. The powders and gels were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis-differential scanning calorimetry （TGA-DSC）. The results indicated that a stable precursor sol was formed when n（CA）：n（Mn＋）= 3：1, n（EDTA）：n（NH4OH） = 1：3.5, and n（CA）：n（EG） = 1：2. The xerogel was calcined at 500-950 ℃ to prepare the KNN powder. Pure KNN perovskite phase with a cube-like structure was synthesized at 850 ℃ from the precursor sol for a K/Na molar ratio of 1.2. The formation mechanism of the KNN perovskite phase was also discussed.
基金Project( 10474077) supported by the National Natural Science Foundation of China Project(2002CB613304) supported by the National Basic Research Program of China
文摘The lead-free piezoelectric ceramics (1-x)(K0.5Na0.5)NbO3-xLiNbO3(abbreviated as KNLN) were synthesized by a traditional solid state reaction. The effects of Li+ on the sintering characteristic, the phase structure and piezoelectric properties of KNLN ceramics were investigated. The sintering temperature of KNN-based ceramics is decreased by doping Li+ and the range of the sintering temperature is narrow. The KNLN ceramics exhibit an enhanced piezoelectric properties with the piezoelectric constant d33 value of 180-200 pC/N, The electromechanical coupling coefficients kp is 35%-40%. The results show that (1-x)(K0.5Na0.5)-NbO3-xLiNbO3 (x=0.05, 0.06) is a promising high-temperature lead free piezoelectric ceramic.
基金National Natural Science Foundation of China(Grant Nos.51572143,51822206,and 51932010).
文摘The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The results reveale that the piezoelectricity stems from strong hybridization between the Nb atom and the O atom.At the same time,the K or Na atoms are replaced by the La doping atoms,which brings about the anisotropic relaxation.The La doping reduces the forbidden band,at the same time it makes Fermi surfaces shift toward the energetic conduction band(CB)of KNN.With the increase of La-doping intent,the phase structure of KNN extends from O-phase to T-phase and improves the piezoelectric properties of KNN.
