The sodium(Na)and Ce co-doped calcium bismuth titanate(CBT;CaBi_(4)Ti_(4)O_(15))Aurivillius ceramics in a Ca_(1-x)(Na_(0.5)Ce_(0.5)),Bi_(4)Ti_(4)O_(15)(CNCBT;doping content(x)=0,0.03,0.05,0.08 and 0.12)system were syn...The sodium(Na)and Ce co-doped calcium bismuth titanate(CBT;CaBi_(4)Ti_(4)O_(15))Aurivillius ceramics in a Ca_(1-x)(Na_(0.5)Ce_(0.5)),Bi_(4)Ti_(4)O_(15)(CNCBT;doping content(x)=0,0.03,0.05,0.08 and 0.12)system were synthesized by the conventional solid-state sintering method.All compositions show a single-phase orthorhombic(space group:A2jam)structure at room temperature.The shift of the Curie point(T_(c))towards lower temperatures(T)on doping results from the increased tolerance factor(t).The substitution-enhanced ferroelectric performance with large maximum polarization(P_(m))and facilitated domain switching is evidenced by the developed electrical polarization-electric field(P-E)and electrical current-electric field(I-E)hysteresis loops.The piezoelectric coefficient(d_(33)=20.5±0.1 pC/N)of the x=0.12 sample is about four times larger than that of pure CBT.The improved piezoelectric properties can be attributed to the high remanent polarization(P_(r))and relatively high dielectric permittivity(ε′).In addition,multi-sized(micron and sub-micron)domain structures were observed in the CNCBT ceramics by the piezoresponse force microscope(PFM).The multiple-sized ferroelectric domain structure with smaller domains is beneficial to the easy domain switching,enhanced ferroelectric performance,and improved piezoelectric properties of the CNCBT ceramics.The designed Aurivillius-phase ferroelectric ceramics with the T_(c) around 765℃and high piezoelectric coefficient(d_(33))are suitable for high-temperature piezoelectric applications.展开更多
Ferroelectric(FE)thin films have recently attracted renewed interest in research due to their great potential for designing novel tunable electromagnetic devices such as large intelligent surfaces(LISs).However,the me...Ferroelectric(FE)thin films have recently attracted renewed interest in research due to their great potential for designing novel tunable electromagnetic devices such as large intelligent surfaces(LISs).However,the mechanism of how a polar structure in the FE thin films contributes to desired tunable performance,especially within the microwave frequency range,which is the most widely used frequency range of electromagnetics,has not been illustrated clearly.In this paper,we described several straightforward and cost-effective methods to fabricate and characterize Ba_(0.6)Sr_(0.4)TiO_(3)(BST)thin films at microwave frequencies.The prepared BST thin films here exhibit homogenous structures and great tunability(h)in a wide frequency and temperature range when the applied field is in the out-of-plane direction.The high tunability can be attributed to high concentration of polar nanoclusters.Their response to the applied direct current(DC)field was directly visualized using a novel non-destructive near-field scanning microwave microscopy(NSMM)technique.Our results have provided some intriguing insights into the application of the FE thin films for future programmable high-frequency devices and systems.展开更多
1.Introduction,In the search for advanced multifunctional materials for next generation sensors and logic devices,magnetoelectric multifer-roics exhibiting simultaneously ferromagnetism and ferroelectric-ity within th...1.Introduction,In the search for advanced multifunctional materials for next generation sensors and logic devices,magnetoelectric multifer-roics exhibiting simultaneously ferromagnetism and ferroelectric-ity within the same phase have received considerable attention in recent years[1-4].展开更多
Novel high-entropy perovskite-type(Ca_(0.2)Sr_(0.2)Ba_(0.2)La_(0.2)Pb_(0.2))TiO_(3)(CSBLP)ceramics with cubic structure of Pm-3 m space group were successful prepared by solid-state reaction method.Results of XRD,SEM-...Novel high-entropy perovskite-type(Ca_(0.2)Sr_(0.2)Ba_(0.2)La_(0.2)Pb_(0.2))TiO_(3)(CSBLP)ceramics with cubic structure of Pm-3 m space group were successful prepared by solid-state reaction method.Results of XRD,SEM-EDS,HRTEM confirmed a homogeneous distribution and equimolar arrangement of multicomponent cations on the A-site.The high-entropy CSBLP ceramics showed long-range structural order and short-range chemical disorder with widely dispersed nanoscale grains varying sizes of 4-6 nm in the microstructure.Because of increased configurational entropy,the CSBLP ceramic has an enhanced Seebeck coefficient(|S|=272μV/K at 1073 K)and low thermal conductivity(k=1.75 W/m·K at 1073 K)when annealed at1300℃.This work demonstrates the possibility of effectively reducing thermal conductivity and improving the performance of thermoelectric oxides through high-entropy composition design.展开更多
Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those co...Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those contributions can affect the shape of the electric displacement-electricfield loops(D-E loops).The effects of frequency,temperature and microstructure(point defects,grain size and texture)on the ferroelectric properties of several ferroelectric compositions is reported,including.BaTiO_(3);lead zirconate titanate(PZT);lead-free Na_(0.5)K_(0.5)NbO_(3);perovskite-like layer structured A_(2)B_(2)O_(7)with super high Curie point(T_(c));Aurivillius phase ferroelectric Bi_(3.15)Nd_(0.85)Ti_(3)O_(12);and multiferroic Bi_(0.89)La_(0.05)Tb_(0.06)FeO_(3).This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.展开更多
Lead-free alkali niobates Na_(0.5)K_(0.5)NbO_(3)(NKN)ceramics,with significantly enhanced ferroelectric remanent polarization(Pr),were prepared using Spark Plasma Sintering(SPS).Three types of boundaries were observed...Lead-free alkali niobates Na_(0.5)K_(0.5)NbO_(3)(NKN)ceramics,with significantly enhanced ferroelectric remanent polarization(Pr),were prepared using Spark Plasma Sintering(SPS).Three types of boundaries were observed in the ceramics,being grain boundaries between faceted grains,domain boundaries that separate ferroelectric domains inside individual grains,and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains.Part of the sub-grain boundaries were from initial powder particles.The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process.It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes.These sub-grain features would disappear at higher temperature by long time sintering.Rapid Spark Plasma Sintering allowed us to capture this transient microstructure.The significantly enhanced ferroelectric Pr of NKN was attributed to nanoscale sub-boundaries,which stimulated the dynamics of ferroelectric domain formation and switching.展开更多
Herein,Ag_(1-3x)Sm_(x)NbO_(3)(0≤x≤0.025)antiferroelectric ceramics were successfully synthesized by solid state methods.The effect of Sm 3þdoping on the structure,property and energy storage performance were st...Herein,Ag_(1-3x)Sm_(x)NbO_(3)(0≤x≤0.025)antiferroelectric ceramics were successfully synthesized by solid state methods.The effect of Sm 3þdoping on the structure,property and energy storage performance were studied.With the increasing Sm^(3+)concentrations,the average grain size decreased.Meanwhile,the stability of high temperature M phases(i.e.,the structure between T_(f) and T_(3))was expanded,which led to low loss for energy storage.Both of structure analysis and ferroelectric tests revealed the existence of weakly polar/AFE-like phase below T_(f).The Sm 3þdoping tended to suppress the ferroelectric behavior and expand the stability of antiferroelectricity.Consequently,a significantly enhanced energy storage performance(W_(rec)=3.8 J/cm^(3),η=73%)could be achieved in Ag_(0.97)Sm_(0.01)NbO_(3) ceramic,which was almost 1.5 times larger than that in non-doped AgNbO_(3)(W_(rec)=2.4 J/cm^(3),η=45%)under the similar applied field of 1705 kV/cm±.In particular,the performance of the ceramic showed great temperature stability with variation of±5%from 25℃ to 125℃.These results indicated that the Ag_(0.97)Sm_(0.01)NbO_(3) ceramic could be an ideal lead-free candidate used in the energy storage field.展开更多
Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with 3reat potential in anti-counterfeiting and data storage applications.Here,Sm^(3+)-doped KSr_(2)Nb_(5)O_(15...Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with 3reat potential in anti-counterfeiting and data storage applications.Here,Sm^(3+)-doped KSr_(2)Nb_(5)O_(15) photochromic ceramics exhibit superior anti-counterfeiting ability:good covertness and considerable modulation ratio of luminescent emission intensity after photochromic reaction.The results show that the photochromism originated from oxygen and cation vacancies,which were directly identified by electron paramagnetic resonance and positron annihilation lifetime spectra.Unexpectedly,oxygen vacancies work more effectively than cation vacancies during photochromic reactions.Moreover,the extraordinary anti-counterfeiting ability was attributed to the high energy transfer rate,which was particularly caused by the short mean distance below 1 nm between the Sm^(3+) and vacancies.The work here has provided atomic-scale structural evidence and made a progress in understanding the photochromic origins and mechanism in color-center theory.展开更多
As a high-temperature thermoelectric(TE)material,ZnO offers advantages of non-toxicity,chemical stability,and oxidation resistance,and shows considerable promise as a true ready-to-use module under air conditions.Howe...As a high-temperature thermoelectric(TE)material,ZnO offers advantages of non-toxicity,chemical stability,and oxidation resistance,and shows considerable promise as a true ready-to-use module under air conditions.However,poor electrical conductivity and high thermal conductivity severely hinder its application.Carbon nanotubes(CNTs)are often used as a reinforcing phase in composites,but it is difficult to achieve uniform dispersion of CNTs due to van der Waals forces.Herein,we developed an effective in-situ growth strategy of homogeneous CNTs on ZnO nanoparticles by exploiting the chemical vapor deposition(CVD)technology,in order to improve their electrical conductivity and mechanical properties,as well as reducing the thermal conductivity.Meanwhile,magnetic nickel(Ni)nanoparticles are introduced as catalysts for promoting the formation of CNTs,which can also enhance the electrical and thermal transportation of ZnO matrices.Notably,the electrical conductivity of ZnO is significantly boosted from 26 to 79 S·cm^(−1) due to the formation of dense and uniform conductive CNT networks.The lattice thermal conductivity(κ_(L))is obviously declined by the intensification of phonon scattering,resulting from the abundant grain boundaries and interfaces in ZnO-CNT composites.Importantly,the maximum dimensionless figure of merit(zT)of 0.04 at 800 K is obtained in 2.0%Ni-CNTs/ZnO,which is three times larger than that of CNTs/ZnO prepared by traditional ultrasonic method.In addition,the mechanical properties of composites including Vickers hardness(HV)and fracture toughness(K_(IC))are also reinforced.This work provides a valuable reference for dispersing nano-phases in TE materials to enhance both TE and mechanical properties.展开更多
Ferroelectric polymer poly(vinylidene fluoride)(PVDF)shows excellent electro-activity and is promising for flexible electronic devices.However,the processing of PVDF into the favourable ferroelectric structure(β-phas...Ferroelectric polymer poly(vinylidene fluoride)(PVDF)shows excellent electro-activity and is promising for flexible electronic devices.However,the processing of PVDF into the favourable ferroelectric structure(β-phase)presents difficulties,while its copolymer with trifluoroethylene(PVDF-TrFE)can directly crystallize into β-phase,but shows limited thermal stability and high-cost processing.As a result,an easily implementable method,pressing-and-folding(P&F),was used to produce highly compatible blended films of PVDF and PVDF-TrFE without using any hazardous solvent or complex polymer processing equipment.Hot-pressed PVDF(molecular weight:530 kg/mol)and PVDF-TrFE(molar ratio:51/49)films were firstly stacked before undergoing P&F treatment.Compared to extrusion-blended films before and after P&F,the P&F stacked films showed isotropic crystalline structure of b-phase,as confirmed using X-ray diffraction and infrared spectroscopy.The ferroelectric remnant polarization of the P&F stacked films is 0.068 C/m^(2),surpassing pure PVDF-TrFE(0.062 C/m^(2))and the simulated value of remnant polarization of pure PVDF(~0.065 C/m^(2)).The above findings promise to provide inspirations for new processing strategy on PVDF-based functional polymers.展开更多
Cu nanowires covered by Ag particles is studied for potential applications in the next-generation microelectronics.To date,the deformation mechanism in the Cu-Ag core-particle is not clear.Here,molecular dynamics simu...Cu nanowires covered by Ag particles is studied for potential applications in the next-generation microelectronics.To date,the deformation mechanism in the Cu-Ag core-particle is not clear.Here,molecular dynamics simulation is used to describe the Cu-Ag core-particle system.The results show that the equilibrium structure of Ag particles is reconstructed,when the particle≤1.0 nm.At low temperature(1 K)indicate that three different deformation processes take part in the core-particle structure,depending on the size of Ag particles.When the particle diameter≤2.0 nm,the prevailing deformation mechanism is the emission of dislocations from the Cu surface.For the particle diameters ranging from 3.0 to 6.0 nm,the emission of misfit dislocations from the Ag-Cu interface is the dominant deformation mechanism.If the Ag particle≥6.0 nm,the deformation mechanism can be characterized by the slip band,consisting of the dislocations and amorphous atoms.For elevated temperatures(2-400 K),the mechanical properties of the Ag-Cu core-shell system are nearly independent of temperature,whereas the structure with particles larger than 2.0 nm showed a strong dependence of its mechanical properties on temperature.Based on the results,the diameter-temperature plastic deformation map is proposed.展开更多
Ca_(5)Nb_(4)TiO_(17) ceramics with 0≤x≤0.4 were prepared through a solid-state reaction method.Effects of zinc substitution on sintering behavior and microwave dielectric properties of Ca_(5)Nb_(4)TiO_(17) ceramics ...Ca_(5)Nb_(4)TiO_(17) ceramics with 0≤x≤0.4 were prepared through a solid-state reaction method.Effects of zinc substitution on sintering behavior and microwave dielectric properties of Ca_(5)Nb_(4)TiO_(17) ceramics were investigated.The sintering temperature was significantly lowered from 1480℃for pure Ca_(5)Nb_(4)TiO_(17) to 1260℃ for x=0.4.The microwave dielectric properties are strongly correlated with the composition.It is worth noting that the temperature cofficient of resonant frequency(τf)displays a tendency toward positive value,ranging from-126.4 ppm/℃ to-8.6 ppm/℃.A temperature stable microwave ceramic with dielectric constant of 52 and Q×f value of 9937GHz is achieved at x=0.4 and is a potential candidate for application as cores in dielectrically loaded antennas.展开更多
A series of ceramics with a general formula,La_(2)Ti_(2-x)Ta_(x)O_(7),in which x=0.05;0.1;0.2;and 0.3,were prepared by Spark Plasma Sintering(SPS).Effects of tantalum substitution for titanium on the structure,dielect...A series of ceramics with a general formula,La_(2)Ti_(2-x)Ta_(x)O_(7),in which x=0.05;0.1;0.2;and 0.3,were prepared by Spark Plasma Sintering(SPS).Effects of tantalum substitution for titanium on the structure,dielectric,and piezoelectric properties were studied.Results revealed that the structure changed gradually from 4-layer to 3-layer due to the higher valence of Ta.The solid solution limit of tantalum in La_(2)Ti_(2)O_(7)lattice was in the proximity of x=0.2.The ferroelectric Curie temperature(Tc)decreased with increasing tantalum doping content.dc resistivity reached a maximum value at x=0.2 with a value of~1.0×10^(8)Ωcm at 600℃.The influence of texture on the piezoelectric properties of La_(2)Ti_(2-x)Ta_(x)O_(7)ceramics was also investigated.A maximum d_(33)value~2:1 pC/N was obtained at x=0.2.展开更多
基金supported by the National Key R&D Program of China(Grant No.2022YFB3807404)the National Natural Science Foundation of China(Grant No.U19A2087)+1 种基金Zimeng Hu would like to acknowledge the China Scholarship Council(Grant No.201806370199)for supporting this workVladimir Koval acknowledges the support of the Grant Agency of the Slovak Academy of Sciences(Grant No.2/0034/23).
文摘The sodium(Na)and Ce co-doped calcium bismuth titanate(CBT;CaBi_(4)Ti_(4)O_(15))Aurivillius ceramics in a Ca_(1-x)(Na_(0.5)Ce_(0.5)),Bi_(4)Ti_(4)O_(15)(CNCBT;doping content(x)=0,0.03,0.05,0.08 and 0.12)system were synthesized by the conventional solid-state sintering method.All compositions show a single-phase orthorhombic(space group:A2jam)structure at room temperature.The shift of the Curie point(T_(c))towards lower temperatures(T)on doping results from the increased tolerance factor(t).The substitution-enhanced ferroelectric performance with large maximum polarization(P_(m))and facilitated domain switching is evidenced by the developed electrical polarization-electric field(P-E)and electrical current-electric field(I-E)hysteresis loops.The piezoelectric coefficient(d_(33)=20.5±0.1 pC/N)of the x=0.12 sample is about four times larger than that of pure CBT.The improved piezoelectric properties can be attributed to the high remanent polarization(P_(r))and relatively high dielectric permittivity(ε′).In addition,multi-sized(micron and sub-micron)domain structures were observed in the CNCBT ceramics by the piezoresponse force microscope(PFM).The multiple-sized ferroelectric domain structure with smaller domains is beneficial to the easy domain switching,enhanced ferroelectric performance,and improved piezoelectric properties of the CNCBT ceramics.The designed Aurivillius-phase ferroelectric ceramics with the T_(c) around 765℃and high piezoelectric coefficient(d_(33))are suitable for high-temperature piezoelectric applications.
基金This work was supported by the“Software Defined Materials for Dynamic Control of Electromagnetic Waves”(ANIMATE)Project(QinetiQ IRAD Grant No.41025673 and EPSRC Grant No.EP/R035393/1),and the authors acknowledge QinetiQ and Engineering and Physical Sciences Research Council(EPSRC).Hanchi Ruan acknowledges EPSRC for funding the Ph.D.studentship.
文摘Ferroelectric(FE)thin films have recently attracted renewed interest in research due to their great potential for designing novel tunable electromagnetic devices such as large intelligent surfaces(LISs).However,the mechanism of how a polar structure in the FE thin films contributes to desired tunable performance,especially within the microwave frequency range,which is the most widely used frequency range of electromagnetics,has not been illustrated clearly.In this paper,we described several straightforward and cost-effective methods to fabricate and characterize Ba_(0.6)Sr_(0.4)TiO_(3)(BST)thin films at microwave frequencies.The prepared BST thin films here exhibit homogenous structures and great tunability(h)in a wide frequency and temperature range when the applied field is in the out-of-plane direction.The high tunability can be attributed to high concentration of polar nanoclusters.Their response to the applied direct current(DC)field was directly visualized using a novel non-destructive near-field scanning microwave microscopy(NSMM)technique.Our results have provided some intriguing insights into the application of the FE thin films for future programmable high-frequency devices and systems.
基金This work was financially supported by the China Scholarship Council(CSC,Nos.201706370172 and 201706370217)The Grant Agency of the Slovak Academy of Sciences(No.2/0038/20)+1 种基金the Slovak Research and Development Agency through grants APVV-20-0072 and SK-CN-2017-0004(for V.Koval)are acknowledged.The National Natural Science Foundation of China(Nos.91963201 and 12174164)the 111 Project(No.B2006)(for C.Jia)are acknowledged.J.Wu and H.Yan thank the financial support from the Royal Society for a Newton Advanced Fellowship award(No.NAF\R1\201126).
文摘1.Introduction,In the search for advanced multifunctional materials for next generation sensors and logic devices,magnetoelectric multifer-roics exhibiting simultaneously ferromagnetism and ferroelectric-ity within the same phase have received considerable attention in recent years[1-4].
基金supported by the China-Poland International Collaboration Fund of National Natural Science Foundation of China(No.51961135301)National Natural Science Foundation of China(52072301)+1 种基金the International Cooperation Foundation of Shaanxi Province(2020KW-032)the‘111’Project(No.B20028)。
文摘Novel high-entropy perovskite-type(Ca_(0.2)Sr_(0.2)Ba_(0.2)La_(0.2)Pb_(0.2))TiO_(3)(CSBLP)ceramics with cubic structure of Pm-3 m space group were successful prepared by solid-state reaction method.Results of XRD,SEM-EDS,HRTEM confirmed a homogeneous distribution and equimolar arrangement of multicomponent cations on the A-site.The high-entropy CSBLP ceramics showed long-range structural order and short-range chemical disorder with widely dispersed nanoscale grains varying sizes of 4-6 nm in the microstructure.Because of increased configurational entropy,the CSBLP ceramic has an enhanced Seebeck coefficient(|S|=272μV/K at 1073 K)and low thermal conductivity(k=1.75 W/m·K at 1073 K)when annealed at1300℃.This work demonstrates the possibility of effectively reducing thermal conductivity and improving the performance of thermoelectric oxides through high-entropy composition design.
基金This work was supported by the UK Royal Society International Joint Project(2009/R2)Xi'an Jiaotong University international incoming short visits(2008 and 2009).
文摘Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those contributions can affect the shape of the electric displacement-electricfield loops(D-E loops).The effects of frequency,temperature and microstructure(point defects,grain size and texture)on the ferroelectric properties of several ferroelectric compositions is reported,including.BaTiO_(3);lead zirconate titanate(PZT);lead-free Na_(0.5)K_(0.5)NbO_(3);perovskite-like layer structured A_(2)B_(2)O_(7)with super high Curie point(T_(c));Aurivillius phase ferroelectric Bi_(3.15)Nd_(0.85)Ti_(3)O_(12);and multiferroic Bi_(0.89)La_(0.05)Tb_(0.06)FeO_(3).This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.
基金This work was supported by grants of the Swedish Research Council(to Z.S.and L.B.)the Royal Society(to Z.S.and H.Y.)+1 种基金the National Natural Science Foundation of China(to C.N.and Z.S.)L.B.acknowledges support from the Knut and Alice Wallenberg Foundation and the Swedish Foundation for Strategic Research.SEM and TEM studies were performed at the Electron Microscopy Centre at Arrhenius Laboratory,Stockholm University,which is supported by the Knut and Alice Wallenberg Foundation.
文摘Lead-free alkali niobates Na_(0.5)K_(0.5)NbO_(3)(NKN)ceramics,with significantly enhanced ferroelectric remanent polarization(Pr),were prepared using Spark Plasma Sintering(SPS).Three types of boundaries were observed in the ceramics,being grain boundaries between faceted grains,domain boundaries that separate ferroelectric domains inside individual grains,and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains.Part of the sub-grain boundaries were from initial powder particles.The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process.It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes.These sub-grain features would disappear at higher temperature by long time sintering.Rapid Spark Plasma Sintering allowed us to capture this transient microstructure.The significantly enhanced ferroelectric Pr of NKN was attributed to nanoscale sub-boundaries,which stimulated the dynamics of ferroelectric domain formation and switching.
基金This work was supported by the National Nature Science Foundation of China(Grant Nos.51772239,51972262 and 51761145024)the Postdoctoral Science Foundation of China(Grant No.2019M653604)+1 种基金the Fundamental Research Funds for the Cen-tral Universities,and“111”Project(No.B14040)the financial support from Shaanxi province(2017ktpt-21).
文摘Herein,Ag_(1-3x)Sm_(x)NbO_(3)(0≤x≤0.025)antiferroelectric ceramics were successfully synthesized by solid state methods.The effect of Sm 3þdoping on the structure,property and energy storage performance were studied.With the increasing Sm^(3+)concentrations,the average grain size decreased.Meanwhile,the stability of high temperature M phases(i.e.,the structure between T_(f) and T_(3))was expanded,which led to low loss for energy storage.Both of structure analysis and ferroelectric tests revealed the existence of weakly polar/AFE-like phase below T_(f).The Sm 3þdoping tended to suppress the ferroelectric behavior and expand the stability of antiferroelectricity.Consequently,a significantly enhanced energy storage performance(W_(rec)=3.8 J/cm^(3),η=73%)could be achieved in Ag_(0.97)Sm_(0.01)NbO_(3) ceramic,which was almost 1.5 times larger than that in non-doped AgNbO_(3)(W_(rec)=2.4 J/cm^(3),η=45%)under the similar applied field of 1705 kV/cm±.In particular,the performance of the ceramic showed great temperature stability with variation of±5%from 25℃ to 125℃.These results indicated that the Ag_(0.97)Sm_(0.01)NbO_(3) ceramic could be an ideal lead-free candidate used in the energy storage field.
基金supported by the China-Poland International Collaboration Fund of National Natural Science Foundation of China(No.51961135301)National Natural Science Foundation of China(No.52072301)+1 种基金the International Cooperation Foundation of Shaanxi Province(No.2019 KW-054,2020 KW-032)the‘111’Project(No.B20028).
文摘Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with 3reat potential in anti-counterfeiting and data storage applications.Here,Sm^(3+)-doped KSr_(2)Nb_(5)O_(15) photochromic ceramics exhibit superior anti-counterfeiting ability:good covertness and considerable modulation ratio of luminescent emission intensity after photochromic reaction.The results show that the photochromism originated from oxygen and cation vacancies,which were directly identified by electron paramagnetic resonance and positron annihilation lifetime spectra.Unexpectedly,oxygen vacancies work more effectively than cation vacancies during photochromic reactions.Moreover,the extraordinary anti-counterfeiting ability was attributed to the high energy transfer rate,which was particularly caused by the short mean distance below 1 nm between the Sm^(3+) and vacancies.The work here has provided atomic-scale structural evidence and made a progress in understanding the photochromic origins and mechanism in color-center theory.
基金supported by the National Natural Science Foundation of China(51871053,91963204,and 52174343)Fundamental Research Funds for the Central Universities(2232020A-02)Science and Technology Commission of Shanghai Municipality(Shanghai Administration of Foreign Experts Affairs)(20JC1415200).
文摘As a high-temperature thermoelectric(TE)material,ZnO offers advantages of non-toxicity,chemical stability,and oxidation resistance,and shows considerable promise as a true ready-to-use module under air conditions.However,poor electrical conductivity and high thermal conductivity severely hinder its application.Carbon nanotubes(CNTs)are often used as a reinforcing phase in composites,but it is difficult to achieve uniform dispersion of CNTs due to van der Waals forces.Herein,we developed an effective in-situ growth strategy of homogeneous CNTs on ZnO nanoparticles by exploiting the chemical vapor deposition(CVD)technology,in order to improve their electrical conductivity and mechanical properties,as well as reducing the thermal conductivity.Meanwhile,magnetic nickel(Ni)nanoparticles are introduced as catalysts for promoting the formation of CNTs,which can also enhance the electrical and thermal transportation of ZnO matrices.Notably,the electrical conductivity of ZnO is significantly boosted from 26 to 79 S·cm^(−1) due to the formation of dense and uniform conductive CNT networks.The lattice thermal conductivity(κ_(L))is obviously declined by the intensification of phonon scattering,resulting from the abundant grain boundaries and interfaces in ZnO-CNT composites.Importantly,the maximum dimensionless figure of merit(zT)of 0.04 at 800 K is obtained in 2.0%Ni-CNTs/ZnO,which is three times larger than that of CNTs/ZnO prepared by traditional ultrasonic method.In addition,the mechanical properties of composites including Vickers hardness(HV)and fracture toughness(K_(IC))are also reinforced.This work provides a valuable reference for dispersing nano-phases in TE materials to enhance both TE and mechanical properties.
基金This work is sponsored by National Natural Science Foundation of China(52103024)Fundamental Research Funds for the Central Universities(2232021D-01)+2 种基金Shanghai Pujiang Program(20PJ1400600)the fellowship of the China Postdoctoral Science Foundation(2021M690646)Engineering and Physical Sciences Research Council(EPSRC)(EP/L017695/1).
文摘Ferroelectric polymer poly(vinylidene fluoride)(PVDF)shows excellent electro-activity and is promising for flexible electronic devices.However,the processing of PVDF into the favourable ferroelectric structure(β-phase)presents difficulties,while its copolymer with trifluoroethylene(PVDF-TrFE)can directly crystallize into β-phase,but shows limited thermal stability and high-cost processing.As a result,an easily implementable method,pressing-and-folding(P&F),was used to produce highly compatible blended films of PVDF and PVDF-TrFE without using any hazardous solvent or complex polymer processing equipment.Hot-pressed PVDF(molecular weight:530 kg/mol)and PVDF-TrFE(molar ratio:51/49)films were firstly stacked before undergoing P&F treatment.Compared to extrusion-blended films before and after P&F,the P&F stacked films showed isotropic crystalline structure of b-phase,as confirmed using X-ray diffraction and infrared spectroscopy.The ferroelectric remnant polarization of the P&F stacked films is 0.068 C/m^(2),surpassing pure PVDF-TrFE(0.062 C/m^(2))and the simulated value of remnant polarization of pure PVDF(~0.065 C/m^(2)).The above findings promise to provide inspirations for new processing strategy on PVDF-based functional polymers.
基金financial support of the National Natural Science Foundation of China(51901184,21975204)the 111 Project of China(B08040)+4 种基金the Natural Science Foundation of Shannxi Province(2021JM-061)supported by High Performance Computing Center of NPUsupported by the QMUL ITS Researchthe support of the China Scholarship Council(CSC No.201806290286)the Grant Agency of the Slovak Academy of Sciences(Grant No.2/0038/20).
文摘Cu nanowires covered by Ag particles is studied for potential applications in the next-generation microelectronics.To date,the deformation mechanism in the Cu-Ag core-particle is not clear.Here,molecular dynamics simulation is used to describe the Cu-Ag core-particle system.The results show that the equilibrium structure of Ag particles is reconstructed,when the particle≤1.0 nm.At low temperature(1 K)indicate that three different deformation processes take part in the core-particle structure,depending on the size of Ag particles.When the particle diameter≤2.0 nm,the prevailing deformation mechanism is the emission of dislocations from the Cu surface.For the particle diameters ranging from 3.0 to 6.0 nm,the emission of misfit dislocations from the Ag-Cu interface is the dominant deformation mechanism.If the Ag particle≥6.0 nm,the deformation mechanism can be characterized by the slip band,consisting of the dislocations and amorphous atoms.For elevated temperatures(2-400 K),the mechanical properties of the Ag-Cu core-shell system are nearly independent of temperature,whereas the structure with particles larger than 2.0 nm showed a strong dependence of its mechanical properties on temperature.Based on the results,the diameter-temperature plastic deformation map is proposed.
基金supported by the National Basic Research Program of China(2009CB623306)International Science&Technology Cooperation Program of China(2013DFR50470).
文摘Ca_(5)Nb_(4)TiO_(17) ceramics with 0≤x≤0.4 were prepared through a solid-state reaction method.Effects of zinc substitution on sintering behavior and microwave dielectric properties of Ca_(5)Nb_(4)TiO_(17) ceramics were investigated.The sintering temperature was significantly lowered from 1480℃for pure Ca_(5)Nb_(4)TiO_(17) to 1260℃ for x=0.4.The microwave dielectric properties are strongly correlated with the composition.It is worth noting that the temperature cofficient of resonant frequency(τf)displays a tendency toward positive value,ranging from-126.4 ppm/℃ to-8.6 ppm/℃.A temperature stable microwave ceramic with dielectric constant of 52 and Q×f value of 9937GHz is achieved at x=0.4 and is a potential candidate for application as cores in dielectrically loaded antennas.
基金supported by the National Basic Research Program of China(2009CB623306)International Science&Technology Cooperation Program of China(2013DFR50470)China Scholarship Council。
文摘A series of ceramics with a general formula,La_(2)Ti_(2-x)Ta_(x)O_(7),in which x=0.05;0.1;0.2;and 0.3,were prepared by Spark Plasma Sintering(SPS).Effects of tantalum substitution for titanium on the structure,dielectric,and piezoelectric properties were studied.Results revealed that the structure changed gradually from 4-layer to 3-layer due to the higher valence of Ta.The solid solution limit of tantalum in La_(2)Ti_(2)O_(7)lattice was in the proximity of x=0.2.The ferroelectric Curie temperature(Tc)decreased with increasing tantalum doping content.dc resistivity reached a maximum value at x=0.2 with a value of~1.0×10^(8)Ωcm at 600℃.The influence of texture on the piezoelectric properties of La_(2)Ti_(2-x)Ta_(x)O_(7)ceramics was also investigated.A maximum d_(33)value~2:1 pC/N was obtained at x=0.2.