Rare-earth doped inorganic ferroelectrics are considered as novel photochromic materials,with potential applications for optical switch and information storage(K0.5Na0.5)1–xEuxNbO3(KNN:xEu)ceramics were prepared by h...Rare-earth doped inorganic ferroelectrics are considered as novel photochromic materials,with potential applications for optical switch and information storage(K0.5Na0.5)1–xEuxNbO3(KNN:xEu)ceramics were prepared by high temperature calcination,with precursor powder obtained by hydrothermal method.Strong red emission at 615 nm was observed which corresponds to the 5D0→7F2 transition of Eu3+under excitation of 465 nm.Under UV light irradiation for 3 min,the color of the ceramics turned from milky white to dark gray.The colored samples returned to the original color when heated at 200℃for 10 min,showing strong photochromic behavior.Meanwhile,the luminescence intensity of Eu3+can be tuned without obvious degradation by alternating UV light and heat stimulus.Upon UV light irradiation,large luminescence modulation ratio(ΔRt)up to 83.9%was achieved for KNN:0.06Eu,indicating good luminescence switching behavior.A possible mechanism for non-radiative energy transfer from the luminescent center to the color center was proposed according to their luminescent behavior.展开更多
The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The ...The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The results reveale that the piezoelectricity stems from strong hybridization between the Nb atom and the O atom.At the same time,the K or Na atoms are replaced by the La doping atoms,which brings about the anisotropic relaxation.The La doping reduces the forbidden band,at the same time it makes Fermi surfaces shift toward the energetic conduction band(CB)of KNN.With the increase of La-doping intent,the phase structure of KNN extends from O-phase to T-phase and improves the piezoelectric properties of KNN.展开更多
The origin of a high mechanical quality in CuO-doped （K, Na）NbO3-based ceramics is addressed by considering the correlations between the lattice positions of Cu ions and the hardening effect in K0.48Na0.52＋xNbO3-0....The origin of a high mechanical quality in CuO-doped （K, Na）NbO3-based ceramics is addressed by considering the correlations between the lattice positions of Cu ions and the hardening effect in K0.48Na0.52＋xNbO3-0.01CuO ceramics. The Cu ions simultaneously occupy K/Na and Nb sites of these ceramics with x = 0 and 0.02, only occupy the K/Na site of the ceramics with x= -0.02, and mostly form a secondary phase of the ceramics with x = -0.05. The Cu ions lead to the hardening of ceramics with an increase of Ec and Qm by only occupying the K/Na site, together with the formation of double hysteresis loops in un-poled compositions. A defect model is proposed to illuminate the origin of a high Qm value, that is, the domain stabilization is dominated by the content of relatively mobile O2- ions in the ceramics, which has a weak bonding with CUK/Na defects.展开更多
Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square...Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space.Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics,affording information regarding the switching behavior of different domains.As such,the out-of-plane polarization states of the domains,including amplitudes and phases can be determined.Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale,and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.展开更多
Pure Ko.sNao sNbO3(KNN)and KNN doped with Lit(6%mole),Lat(1.66%,5%,6%mole),and Ti+t(10%mole)were prepared by mixture of oxides using high-energy milling and conventional solid-state reaction.The effects of the dopant ...Pure Ko.sNao sNbO3(KNN)and KNN doped with Lit(6%mole),Lat(1.66%,5%,6%mole),and Ti+t(10%mole)were prepared by mixture of oxides using high-energy milling and conventional solid-state reaction.The effects of the dopant on the physical properties of pure KNN have been evaluated based on the structural,ferroelectric,pyroelectric,and dielectric measurements.The XRD measurements show that KNN pure sample contains a mixture of monoclinic and orthorhombic crystalline phases,with a slightly higher concentration of monoclinic phase.In contrast,all doped samples show a higher concentration of the orthorhombic phase,as well as the presence of a secondary phase(K6Nb10.8O3o),also detected by Raman measurements.The samples with a higher concentration of this secondary phase,also present greater dielectric losses and lower values of remnant polarization.The dielectric measurements allowed us to detect temperatures of structural transitions(orthorhombic-tetragonal,O-T)previous to the ferroelectric paraelectric transition(tetragonal-cubic,T-C),and also in this set of samples,a direct correlation was found between the values of remnant polarization and the corresponding pyroelectric signal response.展开更多
Two-dimensional(2 D)lead-free(K,Na)Nb O3(KNN)micro/nano structures with controllable K/Na ratio were successfully fabricated via a two-step molten salt synthesis(MSS).In this work,the reaction factors,including the pr...Two-dimensional(2 D)lead-free(K,Na)Nb O3(KNN)micro/nano structures with controllable K/Na ratio were successfully fabricated via a two-step molten salt synthesis(MSS).In this work,the reaction factors,including the proportion of molten salts,the types of carbonates,the sintering temperature,and the sintering time,were discussed in detail and the optimized condition was identified.The microstructure of KNN was confirmed by confocal Raman spectroscopy,while piezoresponse force microscopy(PFM)was applied to measure three-dimensional(3 D)morphology and piezoelectric properties of KNN particles.The as-synthesized KNN platelets apparently possess anisotropic morphology and uniform structure,the size of which reaches 5–20μm in length/width and 0.5–1μm in thickness.It should be noted that the K/Na ratios of the KNN crystals are basically consistent while the proportion of salts changes within a certain range.The enrichment of Na element in the products is also observed,which owes to the smaller ionic radius of Na+comparing to that of K+.This result provides a reference for the further preparation of textured ceramics and flexible piezoelectric generators.展开更多
The thermal stability and fatigue resistance of piezoelectric ceramics are of great importance for industrialized application.In this study,the electrical properties of(0.99-x)(K0.48Na0.52)Nb0.975Sb0.025)O3-0.01CaZrO3...The thermal stability and fatigue resistance of piezoelectric ceramics are of great importance for industrialized application.In this study,the electrical properties of(0.99-x)(K0.48Na0.52)Nb0.975Sb0.025)O3-0.01CaZrO3-x(Bi0.5Na0.5)HfO3 ceramics are investigated.When x=0.03,the ceramics exhibit the optimal electrical properties at room temperature and high Curie temperature(Tc=253℃).In addition,the ceramic has outstanding thermal stability(d33≈301 pm/V at 160℃)and fatigue resistance(variation of Pr and d33~10 %after 10^4 electrical cycles).Subsequently,the defect configuration and crystal structure of the ceramics are studied by X-ray diffraction,temperature-dielectric property curves and impedance analysis.On one hand,the doping(Bio sNao.3)HfO3 makes the dielectric constant peaks flatten.On the other hand,the defect concentration and migration are obviously depressed in the doped ceramics.Both of them can enhance the piezoelectrical properties and improve the temperature and cycling reliabilities.The present study reveals that the good piezoelectric properties can be obtained in 0.96(K0.58Na0.52)(Nb0.975Sb.025)O3-0.01CaZrO3-0.03(Bi0.5Na0.5)HfO3 ceramics.展开更多
基金National Natural Science Foundation of China(61605116,51972213)Science and Technology Commission of Shanghai Municipality(15ZR1440600,15520503400)。
文摘Rare-earth doped inorganic ferroelectrics are considered as novel photochromic materials,with potential applications for optical switch and information storage(K0.5Na0.5)1–xEuxNbO3(KNN:xEu)ceramics were prepared by high temperature calcination,with precursor powder obtained by hydrothermal method.Strong red emission at 615 nm was observed which corresponds to the 5D0→7F2 transition of Eu3+under excitation of 465 nm.Under UV light irradiation for 3 min,the color of the ceramics turned from milky white to dark gray.The colored samples returned to the original color when heated at 200℃for 10 min,showing strong photochromic behavior.Meanwhile,the luminescence intensity of Eu3+can be tuned without obvious degradation by alternating UV light and heat stimulus.Upon UV light irradiation,large luminescence modulation ratio(ΔRt)up to 83.9%was achieved for KNN:0.06Eu,indicating good luminescence switching behavior.A possible mechanism for non-radiative energy transfer from the luminescent center to the color center was proposed according to their luminescent behavior.
基金National Natural Science Foundation of China(Grant Nos.51572143,51822206,and 51932010).
文摘The electronic structures of lead-free piezoceramic(K0.5Na0.5)NbO3(KNN)and La-doped KNN((K0.5Na0.5)0.994La0.006NbO3)are studied by using first principles calculation on the basis of density functional theory(DFT).The results reveale that the piezoelectricity stems from strong hybridization between the Nb atom and the O atom.At the same time,the K or Na atoms are replaced by the La doping atoms,which brings about the anisotropic relaxation.The La doping reduces the forbidden band,at the same time it makes Fermi surfaces shift toward the energetic conduction band(CB)of KNN.With the increase of La-doping intent,the phase structure of KNN extends from O-phase to T-phase and improves the piezoelectric properties of KNN.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （NSFC Grant Nos. 11305152, 51272164, 50772068 and 50972095） and Foundation of Doctor Training Program in University and College in China （Grant Nos. 20030610035 and 20080610020）.
文摘The origin of a high mechanical quality in CuO-doped （K, Na）NbO3-based ceramics is addressed by considering the correlations between the lattice positions of Cu ions and the hardening effect in K0.48Na0.52＋xNbO3-0.01CuO ceramics. The Cu ions simultaneously occupy K/Na and Nb sites of these ceramics with x = 0 and 0.02, only occupy the K/Na site of the ceramics with x= -0.02, and mostly form a secondary phase of the ceramics with x = -0.05. The Cu ions lead to the hardening of ceramics with an increase of Ec and Qm by only occupying the K/Na site, together with the formation of double hysteresis loops in un-poled compositions. A defect model is proposed to illuminate the origin of a high Qm value, that is, the domain stabilization is dominated by the content of relatively mobile O2- ions in the ceramics, which has a weak bonding with CUK/Na defects.
基金This work was supported by Science Challenge Project(No.TZ2018003)National Natural Science Foundation of China(Grant Nos.51822206 and 5171101344).
文摘Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space.Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics,affording information regarding the switching behavior of different domains.As such,the out-of-plane polarization states of the domains,including amplitudes and phases can be determined.Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale,and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.
基金The authors express their thanks to CONACYT for funding this research through projects CB-240460 and LN-295261,and to LIDTRA for the facilities in the use of experimental infrastructure.
文摘Pure Ko.sNao sNbO3(KNN)and KNN doped with Lit(6%mole),Lat(1.66%,5%,6%mole),and Ti+t(10%mole)were prepared by mixture of oxides using high-energy milling and conventional solid-state reaction.The effects of the dopant on the physical properties of pure KNN have been evaluated based on the structural,ferroelectric,pyroelectric,and dielectric measurements.The XRD measurements show that KNN pure sample contains a mixture of monoclinic and orthorhombic crystalline phases,with a slightly higher concentration of monoclinic phase.In contrast,all doped samples show a higher concentration of the orthorhombic phase,as well as the presence of a secondary phase(K6Nb10.8O3o),also detected by Raman measurements.The samples with a higher concentration of this secondary phase,also present greater dielectric losses and lower values of remnant polarization.The dielectric measurements allowed us to detect temperatures of structural transitions(orthorhombic-tetragonal,O-T)previous to the ferroelectric paraelectric transition(tetragonal-cubic,T-C),and also in this set of samples,a direct correlation was found between the values of remnant polarization and the corresponding pyroelectric signal response.
基金the financial supports from the National Natural Science Foundation of China(Grant No.51602345)the State Key Laboratory of New Ceramics and Fine Processing Tsinghua University(Grant No.KF201512)+1 种基金Open Fund of State Key Laboratory of Coal Resources and Safe Mining(Grant No.SKLCRSM19KFA13)Fundamental Research Funds for the Central Universities(Grant No.2016QJ01)。
文摘Two-dimensional(2 D)lead-free(K,Na)Nb O3(KNN)micro/nano structures with controllable K/Na ratio were successfully fabricated via a two-step molten salt synthesis(MSS).In this work,the reaction factors,including the proportion of molten salts,the types of carbonates,the sintering temperature,and the sintering time,were discussed in detail and the optimized condition was identified.The microstructure of KNN was confirmed by confocal Raman spectroscopy,while piezoresponse force microscopy(PFM)was applied to measure three-dimensional(3 D)morphology and piezoelectric properties of KNN particles.The as-synthesized KNN platelets apparently possess anisotropic morphology and uniform structure,the size of which reaches 5–20μm in length/width and 0.5–1μm in thickness.It should be noted that the K/Na ratios of the KNN crystals are basically consistent while the proportion of salts changes within a certain range.The enrichment of Na element in the products is also observed,which owes to the smaller ionic radius of Na+comparing to that of K+.This result provides a reference for the further preparation of textured ceramics and flexible piezoelectric generators.
基金Th e study was supported by National Natural Science Foundation of China(Grant Nos.51702119,51702122,and 51972146).
文摘The thermal stability and fatigue resistance of piezoelectric ceramics are of great importance for industrialized application.In this study,the electrical properties of(0.99-x)(K0.48Na0.52)Nb0.975Sb0.025)O3-0.01CaZrO3-x(Bi0.5Na0.5)HfO3 ceramics are investigated.When x=0.03,the ceramics exhibit the optimal electrical properties at room temperature and high Curie temperature(Tc=253℃).In addition,the ceramic has outstanding thermal stability(d33≈301 pm/V at 160℃)and fatigue resistance(variation of Pr and d33~10 %after 10^4 electrical cycles).Subsequently,the defect configuration and crystal structure of the ceramics are studied by X-ray diffraction,temperature-dielectric property curves and impedance analysis.On one hand,the doping(Bio sNao.3)HfO3 makes the dielectric constant peaks flatten.On the other hand,the defect concentration and migration are obviously depressed in the doped ceramics.Both of them can enhance the piezoelectrical properties and improve the temperature and cycling reliabilities.The present study reveals that the good piezoelectric properties can be obtained in 0.96(K0.58Na0.52)(Nb0.975Sb.025)O3-0.01CaZrO3-0.03(Bi0.5Na0.5)HfO3 ceramics.
