The influence of solid-solution temperature on the dissolution of carbide precipitates, the average grain size and the microhardness of the austenite matrix in an Fe-Ni based high strength low thermal expansion （HSLT...The influence of solid-solution temperature on the dissolution of carbide precipitates, the average grain size and the microhardness of the austenite matrix in an Fe-Ni based high strength low thermal expansion （HSLTE） alloy was investigated to obtain the proper temperature range of the solid-solution process. The XRD analysis, microstructure observations, and the theoretical calculations showed that the Mo-rich M2C-type precipitates in the Fe-Ni based HSLTE alloy dissolve completely at about 1100℃. The average grain size of the studied alloys increases from 14 to 46 μm in the temperature range of 1050 to 1200℃. The microhardness of the matrix decreases gust for the sake of solid-solution treatment, but then increases later with increasing solution temperature because of the solution strengthening effect.展开更多
Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method. Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grai...Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method. Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grain, and no impurity phase appears. The results revealed that the La doping can lead to a large change of the activation energy （from 0.2：2 to 0.02 eV）, and thus result in a marked increase in electric conductivity of 2-4 orders of magnitude. The power factor can reach about 1.5×10-4 W.m-1.K-2 in a wide temperature range, which potentially make them attractive for n-type high-temperature thermoelectric materials.展开更多
(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3(KNN–x BLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric pr...(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3(KNN–x BLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as T_C were systematically investigated. The orthorhombic–tetragonal(O–T) two phases were detected in all(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase(CO/C T= 45/55), high piezoelectric properties of d 33= 239 pC/N, k_p= 34%, and P_r = 25.23 μC/cm^2 were obtained at x = 0.04. Moreover, a high T_C = 348 ℃ was also achieved in KNN–x BLZ ceramic at x = 0.04. These results indicate that (1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 system is a promising candidate for high-temperature piezoelectric devices.展开更多
Morphotropic phase boundary(MPB)plays a key role in tuning piezoelectric responses of ferroelectric ceramics.Here,Bi_(0.5)Na_(0.5)TiO_(3)modified BiFeO_(3)-BaTiO_(3)ternary solid solutions of 0.7BiFeO_(3)-(0.3-x)BaTiO...Morphotropic phase boundary(MPB)plays a key role in tuning piezoelectric responses of ferroelectric ceramics.Here,Bi_(0.5)Na_(0.5)TiO_(3)modified BiFeO_(3)-BaTiO_(3)ternary solid solutions of 0.7BiFeO_(3)-(0.3-x)BaTiO_(3)-xBi_(0.5)Na_(0.5)TiO_(3)(referred to as BF-BT-xBNT,0.00≤x≤0.04)were prepared for lead-free piezo-electrics.All the ceramics exhibit an MPB with coexisting rhombohedral(R)and tetragonal(T)phases,and the R/T phase ratio decreases upon increasing x.The increment of BNT promotes the grain growth,lowers the leakage current and Curie temperature(TC),and gradually drives the ferroelectric to relaxor transition.Because of the MPB with appropriate R/T phase ratio,increased grain size and density,and decreased leakage current,the well-balanced performance between d_(33)=206 pC/N and TC=488℃is obtained in x=0.01 case.In addition,the further enhanced in-situ d_(33)=286e347 pC/N is obtained in BF-BT-xBNT ceramics along with the improved depolarization temperature T_(d)from 280 to 312℃,showing a potential application for lead-free piezoceramics at high temperature.展开更多
Chalcostibite(CuSbS2)is composed of earth-abundant elements and has a proper band gap(Eg=1.05 eV)as a thermoelectric(TE)material.Herein,we report the TE properties in the CuSbS2 based composites with a mole ratio of(1...Chalcostibite(CuSbS2)is composed of earth-abundant elements and has a proper band gap(Eg=1.05 eV)as a thermoelectric(TE)material.Herein,we report the TE properties in the CuSbS2 based composites with a mole ratio of(1–x)CuSbS2–x Cu1.8S(x=0,0.1,0.2,0.3),which were prepared by mechanical alloying(MA)combined with spark plasma sintering(SPS).X-ray diffraction(XRD)and back-scattered electron image(BSE)results indicate that a single phase of CuSbS2 is synthesized at x=0 and the samples consist of CuSbS2,Cu3SbS4,and Cu12Sb4S13 at 0.1≤x≤0.3.The correlation between the phase structure,microstructure,and TE transport properties of the bulk samples is established.The electrical conductivity increases from 0.14 to 50.66 S·cm–1 at 723 K and at0≤x≤0.03,while the Seebeck coefficient holds an appropriate value of 190.51μV·K–1.The highest ZT value of 0.17 is obtained at 723 K and at x=0.3 owing to the combination of a high PF183μW·m–1·K–2 and a lowκ0.8 W·m–1·K–1.展开更多
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
The 0.93(Na_(0.5)Bi_(0.5))_(1–x)Sm_(x)TiO_(3)-0.07BaTiO_(3) multifunctional ceramics were prepared by solid-phase reaction method.The phase structure,microstructure,electrical and photoluminescent properties were sys...The 0.93(Na_(0.5)Bi_(0.5))_(1–x)Sm_(x)TiO_(3)-0.07BaTiO_(3) multifunctional ceramics were prepared by solid-phase reaction method.The phase structure,microstructure,electrical and photoluminescent properties were systematically studied.With increasing x,the ceramics undergoes the phase transition from rhombohedral to tetragonal with some rhombohedral distortion,along with a reduced grain size and increased relative density.On the other hand,the Sm^(3+)doping enhances the electric-field driven reversible phase transition and domain size,and reduces the domain walls,thereby contributing to improved piezoelectricity and decreased depolarization temperature(T_(d))from 91℃ to 40℃.Excellent piezoelectric properties of d_(33)=213 pC/N and kp=29.9% are achieved in the x=0.010 ceramic.Under excitation(407 nm),the Sm^(3+)-doped ceramic exhibits bright reddish-orange fluorescence at 564,599,646 nm and 710 nm.A polarization-induced enhancement of photoluminescence is obtained in BNBT-_(x)Sm ceramics with an improved relative intensity of emission band at 646 nm.These results indicate that Sm^(3+)-doped BNBT ceramics show great potential in electro-optic integration and coupling device applications.展开更多
基金This work was financially supported by the S&T Research Development Project of the Ministry of Science and Technology, China (No.05021050).
文摘The influence of solid-solution temperature on the dissolution of carbide precipitates, the average grain size and the microhardness of the austenite matrix in an Fe-Ni based high strength low thermal expansion （HSLTE） alloy was investigated to obtain the proper temperature range of the solid-solution process. The XRD analysis, microstructure observations, and the theoretical calculations showed that the Mo-rich M2C-type precipitates in the Fe-Ni based HSLTE alloy dissolve completely at about 1100℃. The average grain size of the studied alloys increases from 14 to 46 μm in the temperature range of 1050 to 1200℃. The microhardness of the matrix decreases gust for the sake of solid-solution treatment, but then increases later with increasing solution temperature because of the solution strengthening effect.
基金supported by the National Program on Key Basic Research Project ("973 Program")under grant No.2007CB607505the National High Technology Research and Development Program of China under grant No.2009AAO3Z216
文摘Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method. Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grain, and no impurity phase appears. The results revealed that the La doping can lead to a large change of the activation energy （from 0.2：2 to 0.02 eV）, and thus result in a marked increase in electric conductivity of 2-4 orders of magnitude. The power factor can reach about 1.5×10-4 W.m-1.K-2 in a wide temperature range, which potentially make them attractive for n-type high-temperature thermoelectric materials.
基金supported by Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20130006110006)National Natural Science Foundation of China(Grant Nos.51272023 and 51472026)
文摘(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3(KNN–x BLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as T_C were systematically investigated. The orthorhombic–tetragonal(O–T) two phases were detected in all(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase(CO/C T= 45/55), high piezoelectric properties of d 33= 239 pC/N, k_p= 34%, and P_r = 25.23 μC/cm^2 were obtained at x = 0.04. Moreover, a high T_C = 348 ℃ was also achieved in KNN–x BLZ ceramic at x = 0.04. These results indicate that (1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 system is a promising candidate for high-temperature piezoelectric devices.
基金supported by Natural Science Foundation of Guangxi,China(2022GXNSFBA03561219245084)Guangdong Basic and Applied Basic Research Foundation(2020A1515111004)National Natural Science Foundation of China(52032007,52072028),and Foundation for Guangxi Bagui scholars.
文摘Morphotropic phase boundary(MPB)plays a key role in tuning piezoelectric responses of ferroelectric ceramics.Here,Bi_(0.5)Na_(0.5)TiO_(3)modified BiFeO_(3)-BaTiO_(3)ternary solid solutions of 0.7BiFeO_(3)-(0.3-x)BaTiO_(3)-xBi_(0.5)Na_(0.5)TiO_(3)(referred to as BF-BT-xBNT,0.00≤x≤0.04)were prepared for lead-free piezo-electrics.All the ceramics exhibit an MPB with coexisting rhombohedral(R)and tetragonal(T)phases,and the R/T phase ratio decreases upon increasing x.The increment of BNT promotes the grain growth,lowers the leakage current and Curie temperature(TC),and gradually drives the ferroelectric to relaxor transition.Because of the MPB with appropriate R/T phase ratio,increased grain size and density,and decreased leakage current,the well-balanced performance between d_(33)=206 pC/N and TC=488℃is obtained in x=0.01 case.In addition,the further enhanced in-situ d_(33)=286e347 pC/N is obtained in BF-BT-xBNT ceramics along with the improved depolarization temperature T_(d)from 280 to 312℃,showing a potential application for lead-free piezoceramics at high temperature.
基金supported by National Key R&D Program of China (Grant No. 2018YFB0703600)the National Natural Science Foundation of China (Grant No. 11474176)
文摘Chalcostibite(CuSbS2)is composed of earth-abundant elements and has a proper band gap(Eg=1.05 eV)as a thermoelectric(TE)material.Herein,we report the TE properties in the CuSbS2 based composites with a mole ratio of(1–x)CuSbS2–x Cu1.8S(x=0,0.1,0.2,0.3),which were prepared by mechanical alloying(MA)combined with spark plasma sintering(SPS).X-ray diffraction(XRD)and back-scattered electron image(BSE)results indicate that a single phase of CuSbS2 is synthesized at x=0 and the samples consist of CuSbS2,Cu3SbS4,and Cu12Sb4S13 at 0.1≤x≤0.3.The correlation between the phase structure,microstructure,and TE transport properties of the bulk samples is established.The electrical conductivity increases from 0.14 to 50.66 S·cm–1 at 723 K and at0≤x≤0.03,while the Seebeck coefficient holds an appropriate value of 190.51μV·K–1.The highest ZT value of 0.17 is obtained at 723 K and at x=0.3 owing to the combination of a high PF183μW·m–1·K–2 and a lowκ0.8 W·m–1·K–1.
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 work was supported by Natural Science Foundation of Guangxi,China(2022GXNSFBA035612,ZY22096009,AD21075033)Guangdong Basic and Applied Basic Research Foundation(2020A1515111004)+2 种基金Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion(Grant No.MATEC2022KF002)Natural Science Foundation of China(Grant No.51872180)Foundation for Guangxi Bagui scholars.
文摘The 0.93(Na_(0.5)Bi_(0.5))_(1–x)Sm_(x)TiO_(3)-0.07BaTiO_(3) multifunctional ceramics were prepared by solid-phase reaction method.The phase structure,microstructure,electrical and photoluminescent properties were systematically studied.With increasing x,the ceramics undergoes the phase transition from rhombohedral to tetragonal with some rhombohedral distortion,along with a reduced grain size and increased relative density.On the other hand,the Sm^(3+)doping enhances the electric-field driven reversible phase transition and domain size,and reduces the domain walls,thereby contributing to improved piezoelectricity and decreased depolarization temperature(T_(d))from 91℃ to 40℃.Excellent piezoelectric properties of d_(33)=213 pC/N and kp=29.9% are achieved in the x=0.010 ceramic.Under excitation(407 nm),the Sm^(3+)-doped ceramic exhibits bright reddish-orange fluorescence at 564,599,646 nm and 710 nm.A polarization-induced enhancement of photoluminescence is obtained in BNBT-_(x)Sm ceramics with an improved relative intensity of emission band at 646 nm.These results indicate that Sm^(3+)-doped BNBT ceramics show great potential in electro-optic integration and coupling device applications.
