Raman and IR spectra of Nb-doped PTC Ba1-xPbxTiO3 semiconducting ceramics (x = 0,0. 28,0. 296,0. 313,0. 330,0. 370) have been measured, and mode assignments of Raman scattering frequencies and infrared absorption peak...Raman and IR spectra of Nb-doped PTC Ba1-xPbxTiO3 semiconducting ceramics (x = 0,0. 28,0. 296,0. 313,0. 330,0. 370) have been measured, and mode assignments of Raman scattering frequencies and infrared absorption peaks have been made at room temperature. The influence of Pb2+ ions content on resistivity temperature characteristics and vibration spectra for the Ea1-xPbxTiO3, ceramics have been discussed,and the temperature dependence of the Raman spectra in tetragonal and cubic phases have been investigated from 25 to 340℃. The results indicated that the Raman spectra of the paraelectric phase above Curie point are obviously different from that of ferroelectric phase below Curie point are obviously different from that of ferroelectric phase below Curie point for all the samples. Curie point of each sample,which is determined by resistivity-temperature characteristic measurment, is in good agreement with the results of Raman analysis. The ferroelectric phase transition in the PTCR Bai-xPbxTiO3 ceramics belongs to a distortion or displacement transition.展开更多
The increase in energy consumption and its collateral damage on the environment has encouraged the development of environment-friendly ceramic materials with good energy storage properties.In this work,(1-x)Na_(0.5)Bi...The increase in energy consumption and its collateral damage on the environment has encouraged the development of environment-friendly ceramic materials with good energy storage properties.In this work,(1-x)Na_(0.5)Bi_(0.5)TiO_(3)-xCa(Mg_(1/3)Nb_(2/3))O_(3) ceramics were synthesized by the solid-state reaction method.The 0.88Na_(0.5)Bi_(0.5)TiO_(3)-0.12Ca(Mg_(1/3)Nb_(2/3))O_(3) ceramic exhibited a high recoverable energy storage density of 8.1 J/cm3 and energy storage efficiency of 82.4% at 550 kV/cm.The introduction of Ca(Mg_(1/3)Nb_(2/3))O_(3) reduced the grain size and increased the band gap,thereby enhancing the breakdown field strength of the ceramic materials.The method also resulted in good temperature stability(20–140℃),frequency stability(1–200 Hz),and fatigue stability over 10^(6) cycles.In addition,an ultrahigh power density of 187 MW/cm^(3) and a fast charge-discharge rate(t_(0.9)=57.2 ns)can be obtained simultaneously.Finite element method analysis revealed that the decrease of grain size was beneficial to the increase of breakdown field strength.Therefore,the 0.88Na_(0.5)Bi_(0.5)TiO_(3)-0.12Ca(Mg_(1/3)Nb_(2/3))O_(3) ceramics resulted in high energy storage properties with good stability and were promising environment-friendly materials for advanced pulsed power systems applications.展开更多
White body-color （Y, Gd）BxV1-xO4-x ：Eu^3＋ phosphors were prepared by coprecipitation reaction. Under VUV excitation at 147 nm, the red emission colorimetric purity of （Y, Gd） BxV1-xO4-x： Eu^3＋ phosphor is much...White body-color （Y, Gd）BxV1-xO4-x ：Eu^3＋ phosphors were prepared by coprecipitation reaction. Under VUV excitation at 147 nm, the red emission colorimetric purity of （Y, Gd） BxV1-xO4-x： Eu^3＋ phosphor is much better than that of commercial PDP （plasma display panels） phosphor （Y, Gd）BO3：Eu^3＋ . But its relative emission intensity is only about 90% of the commercial phosphor.展开更多
Tm3+-doped transparent oxyfluoride glass ceramics containing BaYbxY((1-x))F5 nanocrystals were prepared via high temperature solid phase melting method,of which up-conversion emission is achieved by the Yb3+-mediated ...Tm3+-doped transparent oxyfluoride glass ceramics containing BaYbxY((1-x))F5 nanocrystals were prepared via high temperature solid phase melting method,of which up-conversion emission is achieved by the Yb3+-mediated energy transfer process.The required photon number of Tm3+ions emissions in BaYbxY(1-x)F5 nanocrystals was calculated through the luminescence spectra,revealing the strong dependence of energy transfer mechanism on Yb3+ions concentration.Meanwhile,based on the fluore scence intensity ratio technology,the effect of different energy transfer mechanism on the temperature sensitivity was investigated by the temperature-dependent luminescence intensity of thermally coupled energy levels of Tm3+:1G4(a),1G4(b).The obtained sensitivity decreases with the increase of Yb3+ions content,which is mainly attributed to the changes in photon absorption process of Tm^3+:1G4(b).展开更多
Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with ...Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with the increase of Pb^(2+) content.The microstructures were observed by scanning electron microscopy.Dielectric measurement was employed to investigate the ferroelectriceparaelectric phase transition behavior.Temperature dependent polarizationeelectric field hysteresis loops were conducted to study the electrocaloric effect(ECE)of the ferroelectric ceramics by indirect methods over a wide temperature range.Direct measurement of temperature change(DT)at room temperature for all samples can achieve 0.79e1.86 K.What's more,a giant ECE(△T=2.05 K,EC strength(△T/△E)=0.51×10^(-6) K m/V,under 40 kV/cm)was obtained in the sample of x=0.35 near phase transition temperature.Our results suggest that the ceramics are promising cooling materials with excellent EC properties for energy related applications.展开更多
A library of ceramic compounds based on the lead-free(K_(x)Na_(1-x))1-yLiy(Nb1-zTaz)O_(3)solid solution has been synthesized and characterized using high-throughput experimentation(HTE)method.The phase space previousl...A library of ceramic compounds based on the lead-free(K_(x)Na_(1-x))1-yLiy(Nb1-zTaz)O_(3)solid solution has been synthesized and characterized using high-throughput experimentation(HTE)method.The phase space previously reported by Saito and Takao has been expanded to{{x,0.1,1.0},{y,0,0.1},{z,0,0.2}},and new phase boundaries are observed.The relative density values show that with the appropriate sintering temperature,~92%of the theoretical density can be reached.The relative permittivity values show that with increasing amount of K+and Ta5+,the dielectric constant values increase.The effect of density on the dielectric constant values is however minimal.Resistivity values ranging from 109 to 1013Ω·cm are obtained for the samples.The piezoelectric charge coefficient values for selected compositions show that higher values are obtained close to the phase boundaries rather than away from them.The properties for the ceramic library using the HTE method are generally 15%-20%less than from the conventional method.This method is therefore more suited for screening of sample compositions than for producing samples with high piezoelectric properties.展开更多
We prepared (1-x)CaTiO3-xLaAlO3 (0 ≤x≤ 1) microwave dielectric ceramics using a conventional two-step solid-state reaction method,and investigated microwave dielectric properties of the ceramics in terms of A/B-site...We prepared (1-x)CaTiO3-xLaAlO3 (0 ≤x≤ 1) microwave dielectric ceramics using a conventional two-step solid-state reaction method,and investigated microwave dielectric properties of the ceramics in terms of A/B-site ionic-parameters.Ionic-parameters such as ionic polarizability,A-site bond valence,and ionic rattling were linked to the microwave dielectric properties.As the LaAlO3 content x in the (1-x)CaTiO3-xLaAlO3 ceramics increased from 0.3 to 0.7,the dielectric constant gradually decreased,which was attributed to the decrease of polarizability deviation and suppression of the cation rattling.The temperature coefficient of the resonant frequency decreased as the content of LaAlO3 increased because of the increase of A-site cation bond valence.The quality factor value (Q × f) increased as LaAlO3 content increased because of the enhancement of the order degree of B-site cation.A significant deterioration of the temperature coefficient of the resonant frequency and Q ×fvalue was observed at the composition x =0.5.These decreases were attributed to a phase transition from orthorhombic crystal (for x ≤ 0.5) to rhombohedral crystal (for x ＞ 0.5).展开更多
The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is benefici...The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.展开更多
Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by t...Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by the sol gel process,calcined at 900℃for 3 h and sintered at 1250○C for 6 h,have been investigated.The phase formation and crystal structure of the samples were checked by X-ray diffraction(XRD)and Raman spectroscopy.The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La;results that have been confirmed by Rietveld Refinement technique.The estimated average crystallite size of the samples was about 23 nm.Dielectric parameters(dielectric permittivity and losses)were determined in the temperature range room temperature(RT)-280℃and in the frequency range 500 Hz-2 MHz.La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature,and the frequency dependence of the permittivity shows that the samples with x=0.00 and x=0.10 reach their resonance frequency.The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1 kHz to 2MHz at various temperatures to confirm the contributions from grains and grain-boundaries.The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters;it was found that the grain boundaries resistance is dominant at room temperature.The frequency dependence of the parameters permittivity,losses and AC conductivity reveals that the relaxation process is of the Maxwell-Wagner type of interfacial polarization.展开更多
Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) cer...Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) ceramics,this study explores Zn_(1-x)Li_(2x)TiO_(3)(O≤×≤1)ceramics using a phase engineering strategy.Our findings reveal that the introduction of Lit into the ZnTiO_(3) system initiates a multiple phase transition,starting at x=0.1.Initially,ilmenite ZnTiO_(3) transforms into a cubic ordered spinel phase(space group P4332).Subsequently,a transition to a disordered spinel phase(space group Fd3m)occurs at x=0.5,culminating in the formation of a monoclinic rock salt-structured LizTiO3 phase.Significantly,two sets of ceramics with near-zero temperature coefficients of resonance frequency(t:)were obtained at x=0.1 and 0.75.Moreover,the quality factor(Qxf)demonstrated a 4.4-fold increase compared to that of ZnTiO_(3) ceramics at x=0.25(105,013 GHz).Additionally,it was observed that the Ti4 polarization in Zn_(1-x)Li_(2x)TiO_(3) ceramics was underestimated by 11.3%-13.3%,causing the measured dielectric constant(e.)exceeding the theoretical dielectric constant(eth).The ionic polarizability of Ti*was adjusted to stabilize around 3.29 A.Evaluation using multiple methods,including Phillips-van Vechten-Levine(P-V-L)theory,Raman vibrational mode analysis,bond valence,bond energy theory,and octahedral distortion,confirms that the Ti-O bonds within the octahedron predominantly affect&r,the increasing lattice energy(U)contributes to the enhancement of Qxf,and the strengthened Li-O bond energy effectively regulates Tr.展开更多
AgNbO_(3) is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricityand ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO_(3) ceramics wasenhanced...AgNbO_(3) is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricityand ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO_(3) ceramics wasenhanced via K-doping and the phase diagram of the (Ag_(1-x)K_(x))NbO_(3) ceramics was upgraded. In details,(Ag_(1-x)K_(x))NbO_(3) ceramics are ferrielectric (FIE) M1 phase as x=5.00-5.50 mol% and ferroelectric (FE) Ophase as x=5.75-6.00 mol% before poling, and FE O phase as x=5.00-6.00 mol% after poling at roomtemperature. With increasing temperature, (Ag_(1-x)K_(x))NbO_(3) ceramics show the phase evolutions from FIEM1, AFE M2 to paraelectric (PE) T phase at x=5.00-5.50 mol% and from FE O, FE T to PE T phase at x=5.75-6.00 mol% before poling, and from FE O, FE T to PE T phase at x=5.00-6.00 mol% after poling.High d33 values of 180 pC/N and 285 pC/N are obtained at the FE O-FE T and FE T-PE T phase boundaries.This work sheds light on a novel and promising lead-free piezoelectric system.展开更多
Recently,high-performance lead zirconate titanate(Pb(Zr_(1-x)Ti_(x))O_(3),PZT)ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range,better temperature stability,as we...Recently,high-performance lead zirconate titanate(Pb(Zr_(1-x)Ti_(x))O_(3),PZT)ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range,better temperature stability,as well as larger piezoelectric properties and higher energy conversion efficiency.In this study,the perovskite-type ferroelectric ceramics with a chemical formula of Pb_(0.99-x)Gd_(0.01)Sr_(x)Zr_(0.53)Ti_(0.47)O_(3)(x=0 and 0.02,abbr.PGZT and PGSZT,respectively)were prepared by the traditional solid-state reaction route.The influences of Sr-doping on the phase structure,dielectric properties,ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated.The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10 Hz and temperature range of 20–100℃.The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT,but also decreases its dielectric loss tangent,with the d_(33) value of 473 pC/N,ε_(r) value of 1586 and tanδvalue of 0.016 found in PGSZT.Also,PGSZT shows a high Curie temperature(T_(C))of 350℃.The underlying mechanisms of the property enhancement were identified as that the introduced Sr^(2+) replaces the volatile Pb^(2+) located at the A-site of the perovskite structure,thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics,consequently enhancing the dielectric and piezoelectric properties of PGZT.On the other hand,the frequency change in the low-frequency range(<1 Hz)played a significant impact on the remanent polarization(P_(r))and internal biased electric field(E_(i))of PGSZT,but the frequency dependence of coercive field(E_(c))tends to diminish in the high-frequency range(≥1 Hz).展开更多
文摘Raman and IR spectra of Nb-doped PTC Ba1-xPbxTiO3 semiconducting ceramics (x = 0,0. 28,0. 296,0. 313,0. 330,0. 370) have been measured, and mode assignments of Raman scattering frequencies and infrared absorption peaks have been made at room temperature. The influence of Pb2+ ions content on resistivity temperature characteristics and vibration spectra for the Ea1-xPbxTiO3, ceramics have been discussed,and the temperature dependence of the Raman spectra in tetragonal and cubic phases have been investigated from 25 to 340℃. The results indicated that the Raman spectra of the paraelectric phase above Curie point are obviously different from that of ferroelectric phase below Curie point are obviously different from that of ferroelectric phase below Curie point for all the samples. Curie point of each sample,which is determined by resistivity-temperature characteristic measurment, is in good agreement with the results of Raman analysis. The ferroelectric phase transition in the PTCR Bai-xPbxTiO3 ceramics belongs to a distortion or displacement transition.
基金This work is supported by the Natural Science Foundation of Shandong Province of China(Nos.ZR2020ME035,ZR2020QE043 and ZR2020QE044)National Natural Science Foundation of China(Nos.51872166 and 52102132)+1 种基金Postdoctoral Research Foundation of China(2017M622196)Opening Project of Key Laboratory of Inorganic Functional Materials and Devices,Chinese Academy of Sciences(KLIFMD201705).
文摘The increase in energy consumption and its collateral damage on the environment has encouraged the development of environment-friendly ceramic materials with good energy storage properties.In this work,(1-x)Na_(0.5)Bi_(0.5)TiO_(3)-xCa(Mg_(1/3)Nb_(2/3))O_(3) ceramics were synthesized by the solid-state reaction method.The 0.88Na_(0.5)Bi_(0.5)TiO_(3)-0.12Ca(Mg_(1/3)Nb_(2/3))O_(3) ceramic exhibited a high recoverable energy storage density of 8.1 J/cm3 and energy storage efficiency of 82.4% at 550 kV/cm.The introduction of Ca(Mg_(1/3)Nb_(2/3))O_(3) reduced the grain size and increased the band gap,thereby enhancing the breakdown field strength of the ceramic materials.The method also resulted in good temperature stability(20–140℃),frequency stability(1–200 Hz),and fatigue stability over 10^(6) cycles.In addition,an ultrahigh power density of 187 MW/cm^(3) and a fast charge-discharge rate(t_(0.9)=57.2 ns)can be obtained simultaneously.Finite element method analysis revealed that the decrease of grain size was beneficial to the increase of breakdown field strength.Therefore,the 0.88Na_(0.5)Bi_(0.5)TiO_(3)-0.12Ca(Mg_(1/3)Nb_(2/3))O_(3) ceramics resulted in high energy storage properties with good stability and were promising environment-friendly materials for advanced pulsed power systems applications.
文摘White body-color （Y, Gd）BxV1-xO4-x ：Eu^3＋ phosphors were prepared by coprecipitation reaction. Under VUV excitation at 147 nm, the red emission colorimetric purity of （Y, Gd） BxV1-xO4-x： Eu^3＋ phosphor is much better than that of commercial PDP （plasma display panels） phosphor （Y, Gd）BO3：Eu^3＋ . But its relative emission intensity is only about 90% of the commercial phosphor.
基金Project supported by the National Natural Science Foundation of China(11774138,11664022,51862020)Foundation of Yunnan Province(2019HC016).
文摘Tm3+-doped transparent oxyfluoride glass ceramics containing BaYbxY((1-x))F5 nanocrystals were prepared via high temperature solid phase melting method,of which up-conversion emission is achieved by the Yb3+-mediated energy transfer process.The required photon number of Tm3+ions emissions in BaYbxY(1-x)F5 nanocrystals was calculated through the luminescence spectra,revealing the strong dependence of energy transfer mechanism on Yb3+ions concentration.Meanwhile,based on the fluore scence intensity ratio technology,the effect of different energy transfer mechanism on the temperature sensitivity was investigated by the temperature-dependent luminescence intensity of thermally coupled energy levels of Tm3+:1G4(a),1G4(b).The obtained sensitivity decreases with the increase of Yb3+ions content,which is mainly attributed to the changes in photon absorption process of Tm^3+:1G4(b).
基金the National Natural Science Foundation of China(Grant Nos.11574057 and 51604087)the Guangdong Provincial Natural Science Foundation of China(Grant No.2016A030313718)the Science and Technology Program of Guangdong Province of China(Grant Nos.2016A010104018,and 2017A010104022).
文摘Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with the increase of Pb^(2+) content.The microstructures were observed by scanning electron microscopy.Dielectric measurement was employed to investigate the ferroelectriceparaelectric phase transition behavior.Temperature dependent polarizationeelectric field hysteresis loops were conducted to study the electrocaloric effect(ECE)of the ferroelectric ceramics by indirect methods over a wide temperature range.Direct measurement of temperature change(DT)at room temperature for all samples can achieve 0.79e1.86 K.What's more,a giant ECE(△T=2.05 K,EC strength(△T/△E)=0.51×10^(-6) K m/V,under 40 kV/cm)was obtained in the sample of x=0.35 near phase transition temperature.Our results suggest that the ceramics are promising cooling materials with excellent EC properties for energy related applications.
基金The research leading to these results has received financial support from the Deutsche Forschungs Gemeinschaft(DFG)under Grant No.SCHN 372/16:1-2.
文摘A library of ceramic compounds based on the lead-free(K_(x)Na_(1-x))1-yLiy(Nb1-zTaz)O_(3)solid solution has been synthesized and characterized using high-throughput experimentation(HTE)method.The phase space previously reported by Saito and Takao has been expanded to{{x,0.1,1.0},{y,0,0.1},{z,0,0.2}},and new phase boundaries are observed.The relative density values show that with the appropriate sintering temperature,~92%of the theoretical density can be reached.The relative permittivity values show that with increasing amount of K+and Ta5+,the dielectric constant values increase.The effect of density on the dielectric constant values is however minimal.Resistivity values ranging from 109 to 1013Ω·cm are obtained for the samples.The piezoelectric charge coefficient values for selected compositions show that higher values are obtained close to the phase boundaries rather than away from them.The properties for the ceramic library using the HTE method are generally 15%-20%less than from the conventional method.This method is therefore more suited for screening of sample compositions than for producing samples with high piezoelectric properties.
文摘We prepared (1-x)CaTiO3-xLaAlO3 (0 ≤x≤ 1) microwave dielectric ceramics using a conventional two-step solid-state reaction method,and investigated microwave dielectric properties of the ceramics in terms of A/B-site ionic-parameters.Ionic-parameters such as ionic polarizability,A-site bond valence,and ionic rattling were linked to the microwave dielectric properties.As the LaAlO3 content x in the (1-x)CaTiO3-xLaAlO3 ceramics increased from 0.3 to 0.7,the dielectric constant gradually decreased,which was attributed to the decrease of polarizability deviation and suppression of the cation rattling.The temperature coefficient of the resonant frequency decreased as the content of LaAlO3 increased because of the increase of A-site cation bond valence.The quality factor value (Q × f) increased as LaAlO3 content increased because of the enhancement of the order degree of B-site cation.A significant deterioration of the temperature coefficient of the resonant frequency and Q ×fvalue was observed at the composition x =0.5.These decreases were attributed to a phase transition from orthorhombic crystal (for x ≤ 0.5) to rhombohedral crystal (for x ＞ 0.5).
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Natural Science Foundation of Shandong Province(No.ZR2020YQ32)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.
文摘Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by the sol gel process,calcined at 900℃for 3 h and sintered at 1250○C for 6 h,have been investigated.The phase formation and crystal structure of the samples were checked by X-ray diffraction(XRD)and Raman spectroscopy.The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La;results that have been confirmed by Rietveld Refinement technique.The estimated average crystallite size of the samples was about 23 nm.Dielectric parameters(dielectric permittivity and losses)were determined in the temperature range room temperature(RT)-280℃and in the frequency range 500 Hz-2 MHz.La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature,and the frequency dependence of the permittivity shows that the samples with x=0.00 and x=0.10 reach their resonance frequency.The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1 kHz to 2MHz at various temperatures to confirm the contributions from grains and grain-boundaries.The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters;it was found that the grain boundaries resistance is dominant at room temperature.The frequency dependence of the parameters permittivity,losses and AC conductivity reveals that the relaxation process is of the Maxwell-Wagner type of interfacial polarization.
基金This work was supported by the National Natural Science Foundation of China(No.52102129)the Hunan Provincial Natural Science Foundation of China(No.2023JJ30138)the science and technology innovation Program of Hunan Province(No.2023RC3094).
文摘Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) ceramics,this study explores Zn_(1-x)Li_(2x)TiO_(3)(O≤×≤1)ceramics using a phase engineering strategy.Our findings reveal that the introduction of Lit into the ZnTiO_(3) system initiates a multiple phase transition,starting at x=0.1.Initially,ilmenite ZnTiO_(3) transforms into a cubic ordered spinel phase(space group P4332).Subsequently,a transition to a disordered spinel phase(space group Fd3m)occurs at x=0.5,culminating in the formation of a monoclinic rock salt-structured LizTiO3 phase.Significantly,two sets of ceramics with near-zero temperature coefficients of resonance frequency(t:)were obtained at x=0.1 and 0.75.Moreover,the quality factor(Qxf)demonstrated a 4.4-fold increase compared to that of ZnTiO_(3) ceramics at x=0.25(105,013 GHz).Additionally,it was observed that the Ti4 polarization in Zn_(1-x)Li_(2x)TiO_(3) ceramics was underestimated by 11.3%-13.3%,causing the measured dielectric constant(e.)exceeding the theoretical dielectric constant(eth).The ionic polarizability of Ti*was adjusted to stabilize around 3.29 A.Evaluation using multiple methods,including Phillips-van Vechten-Levine(P-V-L)theory,Raman vibrational mode analysis,bond valence,bond energy theory,and octahedral distortion,confirms that the Ti-O bonds within the octahedron predominantly affect&r,the increasing lattice energy(U)contributes to the enhancement of Qxf,and the strengthened Li-O bond energy effectively regulates Tr.
基金This work was supported by the National Natural Science Foun-dation of China(No.51802068 and No.52073144)the Natural Sci-ence Foundation of Hebei Province,China(No.E2021201044)+4 种基金the Advanced Talents Incubation Program of the Hebei University,China(No.801260201180)the Natural Science Foundation of Jiangsu Province,China(No.BK20201301)the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KF202005 and No.KF202114)China Postdoctoral Science Foun-dation(No.2021M692491)Guangdong Basic and Applied Basic Research Foundation(No.2020A1515110251).
文摘AgNbO_(3) is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricityand ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO_(3) ceramics wasenhanced via K-doping and the phase diagram of the (Ag_(1-x)K_(x))NbO_(3) ceramics was upgraded. In details,(Ag_(1-x)K_(x))NbO_(3) ceramics are ferrielectric (FIE) M1 phase as x=5.00-5.50 mol% and ferroelectric (FE) Ophase as x=5.75-6.00 mol% before poling, and FE O phase as x=5.00-6.00 mol% after poling at roomtemperature. With increasing temperature, (Ag_(1-x)K_(x))NbO_(3) ceramics show the phase evolutions from FIEM1, AFE M2 to paraelectric (PE) T phase at x=5.00-5.50 mol% and from FE O, FE T to PE T phase at x=5.75-6.00 mol% before poling, and from FE O, FE T to PE T phase at x=5.00-6.00 mol% after poling.High d33 values of 180 pC/N and 285 pC/N are obtained at the FE O-FE T and FE T-PE T phase boundaries.This work sheds light on a novel and promising lead-free piezoelectric system.
基金funded by the Natural Science Foundation of Sichuan Province(Grant No.2024NSFSC0219).
文摘Recently,high-performance lead zirconate titanate(Pb(Zr_(1-x)Ti_(x))O_(3),PZT)ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range,better temperature stability,as well as larger piezoelectric properties and higher energy conversion efficiency.In this study,the perovskite-type ferroelectric ceramics with a chemical formula of Pb_(0.99-x)Gd_(0.01)Sr_(x)Zr_(0.53)Ti_(0.47)O_(3)(x=0 and 0.02,abbr.PGZT and PGSZT,respectively)were prepared by the traditional solid-state reaction route.The influences of Sr-doping on the phase structure,dielectric properties,ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated.The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10 Hz and temperature range of 20–100℃.The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT,but also decreases its dielectric loss tangent,with the d_(33) value of 473 pC/N,ε_(r) value of 1586 and tanδvalue of 0.016 found in PGSZT.Also,PGSZT shows a high Curie temperature(T_(C))of 350℃.The underlying mechanisms of the property enhancement were identified as that the introduced Sr^(2+) replaces the volatile Pb^(2+) located at the A-site of the perovskite structure,thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics,consequently enhancing the dielectric and piezoelectric properties of PGZT.On the other hand,the frequency change in the low-frequency range(<1 Hz)played a significant impact on the remanent polarization(P_(r))and internal biased electric field(E_(i))of PGSZT,but the frequency dependence of coercive field(E_(c))tends to diminish in the high-frequency range(≥1 Hz).
