Lead zirconate titanate(PZT)ceramics are the most widely used commercial piezoelectric ceramics.However,the relationships between structure and properties are still not completely clarified.In this work,a broad invest...Lead zirconate titanate(PZT)ceramics are the most widely used commercial piezoelectric ceramics.However,the relationships between structure and properties are still not completely clarified.In this work,a broad investigation is carried out on commercial PZT 5A,5H and 4D ceramics.X-ray diffraction revealed that these compounds mainly contain a mixture of P4mm and C1m1 phases at room temperature,and poling induces an increased unit cell distortion in both phases and a higher content of the monoclinic phase.In the poled samples,the Curie point shifts towards lower temperatures,contradicting the Abrahams-Kurtz-Jamieson(AKJ)relation for distorted displacive ferroelectrics.The discordance in the phase transition behavior can be attributed to the decreased domain wall density in the PZT systems.Furthermore,the observed increase of the dielectric permittivity from radiofrequency to the THz range is explained by the increase of the ferroelectric distortion associated with the field-induced transitions and decreased domain wall density.A parameterψwas introduced to characterize the asymmetry of ferroelectric hysteresis loops.The higherψvalue of the hard PZT 4D ceramic compared to that of soft PZT 5A and 5H is attributed to the pinning effect of oxygen vacancies on domain walls.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
Mesoporous mesocrystals are highly desired in catalysis,energy storage,medical and many other applications,but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes,which ...Mesoporous mesocrystals are highly desired in catalysis,energy storage,medical and many other applications,but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes,which impede the commercialization of such materials.During the sintering of dense ceramics,coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification,however,coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume.Here we report a chemi-thermal process,during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering.Through this strategy,we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production.The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator.The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets.This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.展开更多
基金supported by the China Scholarship Council(No.202006040021)the Royal Society grant(NAF∖R1∖201126)+4 种基金the National Natural Science Foundation of China(Grant No.12404116)the Postdoctoral Fellowship Program of CPSF(GZC20232832)the Grant Agency of the Slovak Academy of Sciences(Grant VEGA No 2/0034/23)the Engineering and Physical Sciences Research Council(RC Grant reference:EP/Y027752/1)Foundation is gratefully acknowledged for an equipment grant(KAW 2003.0198)for the electron microscopy facilities at Stockholm University.
文摘Lead zirconate titanate(PZT)ceramics are the most widely used commercial piezoelectric ceramics.However,the relationships between structure and properties are still not completely clarified.In this work,a broad investigation is carried out on commercial PZT 5A,5H and 4D ceramics.X-ray diffraction revealed that these compounds mainly contain a mixture of P4mm and C1m1 phases at room temperature,and poling induces an increased unit cell distortion in both phases and a higher content of the monoclinic phase.In the poled samples,the Curie point shifts towards lower temperatures,contradicting the Abrahams-Kurtz-Jamieson(AKJ)relation for distorted displacive ferroelectrics.The discordance in the phase transition behavior can be attributed to the decreased domain wall density in the PZT systems.Furthermore,the observed increase of the dielectric permittivity from radiofrequency to the THz range is explained by the increase of the ferroelectric distortion associated with the field-induced transitions and decreased domain wall density.A parameterψwas introduced to characterize the asymmetry of ferroelectric hysteresis loops.The higherψvalue of the hard PZT 4D ceramic compared to that of soft PZT 5A and 5H is attributed to the pinning effect of oxygen vacancies on domain walls.
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.
文摘Mesoporous mesocrystals are highly desired in catalysis,energy storage,medical and many other applications,but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes,which impede the commercialization of such materials.During the sintering of dense ceramics,coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification,however,coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume.Here we report a chemi-thermal process,during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering.Through this strategy,we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production.The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator.The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets.This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.
