Layered Aurivillius compound Bi_(5)Ti_(3)CrO_(15) has been synthesized by a hydrothermal method for the application as a photocatalyst to liberate hydrogen from water. Bi_(5)Ti_(3)CrO_(15) owns a narrow band gap (Eg ~...Layered Aurivillius compound Bi_(5)Ti_(3)CrO_(15) has been synthesized by a hydrothermal method for the application as a photocatalyst to liberate hydrogen from water. Bi_(5)Ti_(3)CrO_(15) owns a narrow band gap (Eg ~2.46 eV) and shows stable photocatalytic activity under both full range (λ ≥250 nm) and visible light illumination (λ ≥420 nm). A short hydrothermal reaction time is critical to achieve high photocatalytic activity as defects such as Cr^(6+) and Bi^(5+) can be avoided. An AQE as high as 3.66% at 420 nm ± 20 nm has been recorded, warranting promising application in the field of solar energy conversions. DFT calculation reveals the important role of Cr^(3+) cations for visible light sensitivity of Bi_(5)Ti_(3)CrO_(15).展开更多
In this study,the double-layered Aurivillius phases CaBi_(2)Ta_(2)O_(9)(CBT)and PbBi_(2)Ta_(2)O_(9)(PBT)were prepared through a hydrother-mal route with NaOH as a mineralizer.XRD analysis confirmed that the CBT and PB...In this study,the double-layered Aurivillius phases CaBi_(2)Ta_(2)O_(9)(CBT)and PbBi_(2)Ta_(2)O_(9)(PBT)were prepared through a hydrother-mal route with NaOH as a mineralizer.XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A21am symmetry.Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca^(2+)compared to Pb^(2+).The surface mor-phology of both samples,as determined using SEM,demonstrated plate-like grains with anisotropic grain growth.It was found that the different ionic radii of A-site cations(Ca^(2+)and Pb^(2+))strongly affected the structural,optical and electrical properties of the Aurivillius phase.The occupation of smaller Ca^(2+)cations induced a higher structural distortion,which resulted in higher bandgap(Eg)energy and ferroelectric transition temperature(Tc)of CBT,compared to those of PBT.展开更多
Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space g...Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius oxide.The scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius compounds.The temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the material.The diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic disorder.The dielectric relaxation obeyed the VogelFulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve fitting.The temperature dependence of dielectric constant at temperatures much higher and lower than Tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.Various other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.展开更多
In this work, different amount of Cr_(2)O_(3) (x - 0e0.3 wt%) as dopant were doped into the Aurivillius-typecompound Bi2.8Gd0.2TiNbO9 (BGTN), such a kind of Gd/Cr co-doped Bi3TiNbO9 ceramics with improvedelectrical pr...In this work, different amount of Cr_(2)O_(3) (x - 0e0.3 wt%) as dopant were doped into the Aurivillius-typecompound Bi2.8Gd0.2TiNbO9 (BGTN), such a kind of Gd/Cr co-doped Bi3TiNbO9 ceramics with improvedelectrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr^(3+) for Ti^(4+) at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr_(2)O_(3) dopant(x<0.2) resulted in the grain refinement of ceramics. After Cr_(2)O_(3) was added into BGTN, TC decreased tothe vicinity of 908 ℃. Below TC, the relaxed dielectric response resulted from charge carriers hoppinginduced another board dielectric permittivity peak, whose starting temperature shifts toward lower sidegradually with increase of x. The values of Eacon calculated from the Arrhenius relationship betweenconductivity and temperature indicated the intrinsic conduction at high temperature is dominated by thelong-range migration of doubly ionized oxygen vacancies. Moderate Cr_(2)O_(3) dopant (x=0.1e0.25) areconducive to the enhancement of piezoelectric property and thermal stability. The sample with x=0.2 achieved both a high T_(C)~903 - C and a high d_(33)~18 pC/N at the same time. Also, its d33 can retain 80% ofthe initial value after the sample was annealed at 800 - C for 4 h.展开更多
Bi_(5)FeTi_(2.5)Co_(0.5)O_(15)(BFTC)ceramics was successfully synthesized using the sol-gel method.It exhibits simultaneously visible-light response,ferroelectric and weak ferromagnetic orders at room temperature.The ...Bi_(5)FeTi_(2.5)Co_(0.5)O_(15)(BFTC)ceramics was successfully synthesized using the sol-gel method.It exhibits simultaneously visible-light response,ferroelectric and weak ferromagnetic orders at room temperature.The narrow band gap of 2.06 eV was determined via the UVevis diffuse absorption spectrum.The x-ray photoelectron spectroscopy results show that the Fe ions in the samples is 3 t and 2 t valence states while the doped Co ions is 2 t valence state.The BFTC sample undergoes a ferromagnetic-like transition at~552 K.Weak ferromagnetism is mainly due to spin-canting of Fe-based and Co-based sublattices via Dzyaloshinskii-Moriya(DM)interaction.Dielectric loss and dielectric modulus exhibit the characteristics of dielectric relaxation,which can be ascribed to oxygen/vacancy hopping.These results reveal many potentially useful physical phenomena and open a new avenue to design of novel solar-energy conversion devices and multiferroic applications.展开更多
This work is devoted to the synthesis and characterization of yttrium-doped SrBi_2Nb_2O_9 ceramics prepared by three methods: solid state reaction, co-precipitation, and hydrothermal. Multiple characterizations, speci...This work is devoted to the synthesis and characterization of yttrium-doped SrBi_2Nb_2O_9 ceramics prepared by three methods: solid state reaction, co-precipitation, and hydrothermal. Multiple characterizations, specifically scanning electron microscopy(SEM), X-ray powder diffraction(XRD), and Fourier transform infrared spectroscopy(FTIR), were used to validate the structural feature. The crystallite size was estimated by Scherrer's formula and the Williamson–Hall plot. The effect of the process on the band intensities of the FTIR spectra was investigated. The crystallite size and microstructure of ceramics prepared from different synthesis processes were strongly influenced by the sinterability. SEM images revealed nanograin ceramics for materials prepared by co-precipitation and hydrothermal methods and micrograin ceramics prepared by the solid state method. The synthesized compounds underwent phase transitions at 480–465°C. The dielectric and electrical properties of these Y-doped SrBi_2Nb_2O_9 ceramics appear to be dependent on the grain size.展开更多
This Ce-doped strontium bismuth tantalate SrBi<sub>1.8</sub>Ce<sub>0.2</sub>Ta<sub>2</sub>O<sub>9</sub> was prepared by solid-state reaction. X-ray diffraction was used ...This Ce-doped strontium bismuth tantalate SrBi<sub>1.8</sub>Ce<sub>0.2</sub>Ta<sub>2</sub>O<sub>9</sub> was prepared by solid-state reaction. X-ray diffraction was used to determine the crystal structure of the powders. The Raman spectrum of SrBi<sub>1.8</sub>Ce<sub>0.2</sub>Ta<sub>2</sub>O<sub>9</sub> sample was measured to confirm X-ray diffraction result. The microstructure of ceramic was observed by Scanning Electron Microscope (SEM). The Temperature dependence of the dielectric properties of ceramic was investigated from the room temperature to 400°C.展开更多
Electrostatic capacitors based on dielectrics with high energy density and efficiency are desired for modern electrical systems owing to their intrinsic fast charging-discharging speed and excellent reliability.The lo...Electrostatic capacitors based on dielectrics with high energy density and efficiency are desired for modern electrical systems owing to their intrinsic fast charging-discharging speed and excellent reliability.The longstanding bottleneck is their relatively small energy density.Herein,we report enhanced energy density and efficiency in the Aurivillius Pb_(2)Bi_(4)Ti_(5)O_(18)films by controlling the post-annealing atmosphere.The results demonstrate that the fabrication atmosphere has significant effects on the film texture and defects.As the increase of the oxygen pressure of annealing atmosphere,the Pb_(2)Bi_(4)Ti_(5)O_(18)films show a preferred growth orientation of(00l)and fewer defects,which leads to a higher polarization and breakdown field for the film annealed in air atmosphere and thus help to achieve an ultrahigh energy density of59.4 J·cm^(-3)and an improved efficiency of 81.2%.Moreover,the film also exhibits excellent cycling reliability and good thermal stability.The Pb_(2)Bi_(4)Ti_(5)O_(18)films show a significant potential application for dielectric capacitors.展开更多
High-quality single crystals of Bi_(2)WO_(6) are grown using a flux method.With different flux growth recipes,we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition ...High-quality single crystals of Bi_(2)WO_(6) are grown using a flux method.With different flux growth recipes,we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature,resulting in mono-domain and multi-domain Bi_(2)WO_(6) crystals,respectively.Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope.PFM studies unveil the 90°polarization change across those ferroelastic domain walls,as well as the absence of 180°ferroelectric domains in the as-grown multi-domain crystals,indicating a high energy cost of 180°ferroelectric domains.Moreover,a 45°tilt of the 90°ferroelectric domain walls is discovered,and this tilt creates a new type of charged 90°ferroelectric walls,which have not been observed in other bulk ferroelectrics.展开更多
Na0.5Bi4.5-xEuxTi4O15 （NBT-xEu^3＋） ceramics with x= 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 and 0.40 were prepared by conventional ceramics processing. NBT-0.25Eu^3＋ ceramics show the strongest red and orange emissi...Na0.5Bi4.5-xEuxTi4O15 （NBT-xEu^3＋） ceramics with x= 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 and 0.40 were prepared by conventional ceramics processing. NBT-0.25Eu^3＋ ceramics show the strongest red and orange emissions corresponding to the 5D0 → 7F2 （617 nm） and 5D0→ 7F1 （596 nm） transitions, respectively. The strongest excitation band around 465 nm matches well with the emission wavelength of commercial InGaN-based blue LED chip, indicating that Eu^3＋-doped NBT ceramics may be used as potential environmental friendly red-orange phosphor for W-LEDs application. As an inherent ferroelectric and piezoelectric material, the electrical properties of this potentially multifunctional electro-optical material have been also studied. The introduction of Eu^3＋ distinctly increased the Curie temperature （Tc） of NBT-xEu^3＋ ceramics from 640℃ to 711℃ as x ranges from 0 to 0.40. For higher temperature applications, the electrical conductivity was also investigated. The conduction of charge carriers in hightemperature range originates from the conducting electrons from the ionization of oxygen vacancies. High Tc and low tanδ makes Eu^3＋-doped NBT ceramic also suitable for high temperature piezoelectric sensor applications and electro-optical integration.展开更多
Ce and W co-doped CaBi_(2)Nb_(2)O_(9) ceramics with chemical formula Ca_(0.96)Ce_(0.04)Bi_(2)Nb_(2-x)W_(x)O_(9)(CCBNW100x,x=0-0.07)are fabricated via conventional solid state sintering method,to investigate the effect...Ce and W co-doped CaBi_(2)Nb_(2)O_(9) ceramics with chemical formula Ca_(0.96)Ce_(0.04)Bi_(2)Nb_(2-x)W_(x)O_(9)(CCBNW100x,x=0-0.07)are fabricated via conventional solid state sintering method,to investigate the effect of W addition on the structure,electrical resistivity,dielectric and piezoelectric properties.A piezoelectric constant d33 of 13.4 pC/N is obtained in CCBN-W2 ceramics,>100% higher than that of pure CaBi_(2)Nb_(2)O_(9)(d_(33)=5.8e6.4 pC/N).Of particular significance is that the electrical resistivity of CCBN-W2 ceramics(r=3.7×109 U cm at 500℃)is three orders of magnitude higher than pure CaBi_(2)Nb_(2)O_(9)(r=2.9×10^(6) U cm at same temperature).All these properties,together with its low dielectric loss(tandδ0.13%)and excellent d33 thermal stability up to 800℃,merit the CCBN-W2 ceramics for high temperature piezoelectric sensing applications.展开更多
Bi_4Ti_3O_(12) is an important lead-free ferroelectric material.Doping modification of Bi_4Ti_3O_(12)has attracted great attention to improving its performances.In this work,the effect of Sr dopants on the microstruct...Bi_4Ti_3O_(12) is an important lead-free ferroelectric material.Doping modification of Bi_4Ti_3O_(12)has attracted great attention to improving its performances.In this work,the effect of Sr dopants on the microstructure,dielectric,and conductivity of Bi_4Ti_3O_(12) ceramic was investigated by XRD,SEM,and AC impedance spectroscopy.Substitution of 1 at%Sr for Bi decreased the grain size,suppressed the dielectric dispersion of Bi_4Ti_3O_(12) ceramic at room temperature,and resulted in different effects on the conductivity of grains and grain boundaries.The conductivity of grains in Bi_4Ti_3O_(12) ceramic was increased by the small amount of Sr dopants in the whole experimental temperature range.While the grain boundaries of 1 at%Sr-doped Bi_4Ti_3O_(12) exhibited lower conductivity than pure Bi_4Ti_3O_(12) below～380℃and higher conductivity above～380℃.The experimental phenomena were interpreted in term of compensating defects for Sr dopants.展开更多
A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of ep...A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of epitaxially grown Co_(3)O_(4) nanopillars embedded in the Bi_(2)WO_(6) matrix with a unique 2D layered structure,as evidenced by the microstructural analysis.Physical property measurements show that the new Bi_(2)WO_(6)-Co_(3)O_(4) VAN structure exhibits strong ferromagnetic and piezoelectric response at room temperature as well as anisotropic permittivity response.This work demonstrates a new approach in processing multifunctional VANs structure based on the layered oxide systems towards future nonlinear optics,ferromagnets,and multiferroics.展开更多
The paper presents the structural and ferroelectric results for Sr_(1-x)Ba_(x)Bi_(2)Nb_(2)O_(9)(x=0.30;0.85)thin films,which were obtained by using dip-coating.The solutions containing the desirable ions were prepared...The paper presents the structural and ferroelectric results for Sr_(1-x)Ba_(x)Bi_(2)Nb_(2)O_(9)(x=0.30;0.85)thin films,which were obtained by using dip-coating.The solutions containing the desirable ions were prepared from the powders of the previous studied ceramic samples.The films were deposited at room temperature on Fluorine-doped Tin Oxide(FTO)substrates and submitted to a heat treatment for crystallization.The films were characterized by using scanning microscopy electronic,energy dispersive spectroscopy and ellipsometry.Hysteresis ferroelectric loops were obtained,at room temperature,by using a Sawyer-Tower circuit at several frequencies.A well-defined grain structure was observed for both compositions.The energy dispersive spectroscopy(EDS)measurements revealed the presence of the corresponding elements from the chemical composition of the ceramic systems.The band-gap energy was around 3.3 eV for both samples.Typical hysteresis loops for normal and relaxor ferroelectrics were obtained for x=0.30 and 0.85,respectively.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.51972233)the Natural Science Foundation of Shanghai(No.19ZR1459200)+1 种基金the Shanghai Science and Technology Commission(No.14DZ2261100)the Fundamental Research Funds for the Central Universities.We also thank Prof.Hongying Zhao for EPR analysis.
文摘Layered Aurivillius compound Bi_(5)Ti_(3)CrO_(15) has been synthesized by a hydrothermal method for the application as a photocatalyst to liberate hydrogen from water. Bi_(5)Ti_(3)CrO_(15) owns a narrow band gap (Eg ~2.46 eV) and shows stable photocatalytic activity under both full range (λ ≥250 nm) and visible light illumination (λ ≥420 nm). A short hydrothermal reaction time is critical to achieve high photocatalytic activity as defects such as Cr^(6+) and Bi^(5+) can be avoided. An AQE as high as 3.66% at 420 nm ± 20 nm has been recorded, warranting promising application in the field of solar energy conversions. DFT calculation reveals the important role of Cr^(3+) cations for visible light sensitivity of Bi_(5)Ti_(3)CrO_(15).
基金This research was funded through PMDSU Scholarship Grant No.050/SP2H/LT/DRPM/2018 sponsored by the Ministry of Research,Technology and Higher Education(RISTEKDIKTI)of The Republic of Indonesia.
文摘In this study,the double-layered Aurivillius phases CaBi_(2)Ta_(2)O_(9)(CBT)and PbBi_(2)Ta_(2)O_(9)(PBT)were prepared through a hydrother-mal route with NaOH as a mineralizer.XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A21am symmetry.Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca^(2+)compared to Pb^(2+).The surface mor-phology of both samples,as determined using SEM,demonstrated plate-like grains with anisotropic grain growth.It was found that the different ionic radii of A-site cations(Ca^(2+)and Pb^(2+))strongly affected the structural,optical and electrical properties of the Aurivillius phase.The occupation of smaller Ca^(2+)cations induced a higher structural distortion,which resulted in higher bandgap(Eg)energy and ferroelectric transition temperature(Tc)of CBT,compared to those of PBT.
文摘Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius oxide.The scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius compounds.The temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the material.The diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic disorder.The dielectric relaxation obeyed the VogelFulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve fitting.The temperature dependence of dielectric constant at temperatures much higher and lower than Tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.Various other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.
基金This work was supported by the National Natural ScienceFoundation of China (Grant No. 11702037, 51932010)China Post-doctoral Science Foundation Funded Project (Grant No.2017M623025)Opening foundation from the Key Laboratory ofDeep Earth Science and Engineering (Sichuan University), Ministryof Education (Grant No. 202007).
文摘In this work, different amount of Cr_(2)O_(3) (x - 0e0.3 wt%) as dopant were doped into the Aurivillius-typecompound Bi2.8Gd0.2TiNbO9 (BGTN), such a kind of Gd/Cr co-doped Bi3TiNbO9 ceramics with improvedelectrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr^(3+) for Ti^(4+) at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr_(2)O_(3) dopant(x<0.2) resulted in the grain refinement of ceramics. After Cr_(2)O_(3) was added into BGTN, TC decreased tothe vicinity of 908 ℃. Below TC, the relaxed dielectric response resulted from charge carriers hoppinginduced another board dielectric permittivity peak, whose starting temperature shifts toward lower sidegradually with increase of x. The values of Eacon calculated from the Arrhenius relationship betweenconductivity and temperature indicated the intrinsic conduction at high temperature is dominated by thelong-range migration of doubly ionized oxygen vacancies. Moderate Cr_(2)O_(3) dopant (x=0.1e0.25) areconducive to the enhancement of piezoelectric property and thermal stability. The sample with x=0.2 achieved both a high T_(C)~903 - C and a high d_(33)~18 pC/N at the same time. Also, its d33 can retain 80% ofthe initial value after the sample was annealed at 800 - C for 4 h.
基金the National Science Foundation of China(Grant No.51402256 and Grant No.11374227)Natural Science Foundation of Jiangsu Province,China(No.BK 20161409)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,China(Grant No.12KJB140013).
文摘Bi_(5)FeTi_(2.5)Co_(0.5)O_(15)(BFTC)ceramics was successfully synthesized using the sol-gel method.It exhibits simultaneously visible-light response,ferroelectric and weak ferromagnetic orders at room temperature.The narrow band gap of 2.06 eV was determined via the UVevis diffuse absorption spectrum.The x-ray photoelectron spectroscopy results show that the Fe ions in the samples is 3 t and 2 t valence states while the doped Co ions is 2 t valence state.The BFTC sample undergoes a ferromagnetic-like transition at~552 K.Weak ferromagnetism is mainly due to spin-canting of Fe-based and Co-based sublattices via Dzyaloshinskii-Moriya(DM)interaction.Dielectric loss and dielectric modulus exhibit the characteristics of dielectric relaxation,which can be ascribed to oxygen/vacancy hopping.These results reveal many potentially useful physical phenomena and open a new avenue to design of novel solar-energy conversion devices and multiferroic applications.
基金National Natural Science Foundation of China(51072136)Specialized Research Fund for the Doctoral Program of Higher Education(20090072120034)Scholarship Award for Excellent Doctorial Student Granted by Ministry of Education(0500219171)
文摘This work is devoted to the synthesis and characterization of yttrium-doped SrBi_2Nb_2O_9 ceramics prepared by three methods: solid state reaction, co-precipitation, and hydrothermal. Multiple characterizations, specifically scanning electron microscopy(SEM), X-ray powder diffraction(XRD), and Fourier transform infrared spectroscopy(FTIR), were used to validate the structural feature. The crystallite size was estimated by Scherrer's formula and the Williamson–Hall plot. The effect of the process on the band intensities of the FTIR spectra was investigated. The crystallite size and microstructure of ceramics prepared from different synthesis processes were strongly influenced by the sinterability. SEM images revealed nanograin ceramics for materials prepared by co-precipitation and hydrothermal methods and micrograin ceramics prepared by the solid state method. The synthesized compounds underwent phase transitions at 480–465°C. The dielectric and electrical properties of these Y-doped SrBi_2Nb_2O_9 ceramics appear to be dependent on the grain size.
文摘This Ce-doped strontium bismuth tantalate SrBi<sub>1.8</sub>Ce<sub>0.2</sub>Ta<sub>2</sub>O<sub>9</sub> was prepared by solid-state reaction. X-ray diffraction was used to determine the crystal structure of the powders. The Raman spectrum of SrBi<sub>1.8</sub>Ce<sub>0.2</sub>Ta<sub>2</sub>O<sub>9</sub> sample was measured to confirm X-ray diffraction result. The microstructure of ceramic was observed by Scanning Electron Microscope (SEM). The Temperature dependence of the dielectric properties of ceramic was investigated from the room temperature to 400°C.
基金financially supported by the National Key Research Program of China (No.2021YFB3800601)the Basic Science Center Project of the National Natural Science Foundation of China (NSFC,No.51788104)。
文摘Electrostatic capacitors based on dielectrics with high energy density and efficiency are desired for modern electrical systems owing to their intrinsic fast charging-discharging speed and excellent reliability.The longstanding bottleneck is their relatively small energy density.Herein,we report enhanced energy density and efficiency in the Aurivillius Pb_(2)Bi_(4)Ti_(5)O_(18)films by controlling the post-annealing atmosphere.The results demonstrate that the fabrication atmosphere has significant effects on the film texture and defects.As the increase of the oxygen pressure of annealing atmosphere,the Pb_(2)Bi_(4)Ti_(5)O_(18)films show a preferred growth orientation of(00l)and fewer defects,which leads to a higher polarization and breakdown field for the film annealed in air atmosphere and thus help to achieve an ultrahigh energy density of59.4 J·cm^(-3)and an improved efficiency of 81.2%.Moreover,the film also exhibits excellent cycling reliability and good thermal stability.The Pb_(2)Bi_(4)Ti_(5)O_(18)films show a significant potential application for dielectric capacitors.
基金supported by the Center for Quantum Materials Synthesis(cQMS)funded by the Gordon and Betty Moore Foundation’s EPiQS initiative through grant GBMF10104by Rutgers University.
文摘High-quality single crystals of Bi_(2)WO_(6) are grown using a flux method.With different flux growth recipes,we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature,resulting in mono-domain and multi-domain Bi_(2)WO_(6) crystals,respectively.Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope.PFM studies unveil the 90°polarization change across those ferroelastic domain walls,as well as the absence of 180°ferroelectric domains in the as-grown multi-domain crystals,indicating a high energy cost of 180°ferroelectric domains.Moreover,a 45°tilt of the 90°ferroelectric domain walls is discovered,and this tilt creates a new type of charged 90°ferroelectric walls,which have not been observed in other bulk ferroelectrics.
基金Acknowledgements This work was financially supported by the National Natural Science Foundation of China （Grant Nos. 51562014 and 51262009）and the Natural Science Foundation of Jiangxi, China （Grant Nos. 20133ACB20002 and 20142BAB216009）, and partially sponsored by Colleges and Universities ＂Advanced Ceramics＂ Scientific and Technological Innovation Team of Jiangxi Province.
文摘Na0.5Bi4.5-xEuxTi4O15 （NBT-xEu^3＋） ceramics with x= 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 and 0.40 were prepared by conventional ceramics processing. NBT-0.25Eu^3＋ ceramics show the strongest red and orange emissions corresponding to the 5D0 → 7F2 （617 nm） and 5D0→ 7F1 （596 nm） transitions, respectively. The strongest excitation band around 465 nm matches well with the emission wavelength of commercial InGaN-based blue LED chip, indicating that Eu^3＋-doped NBT ceramics may be used as potential environmental friendly red-orange phosphor for W-LEDs application. As an inherent ferroelectric and piezoelectric material, the electrical properties of this potentially multifunctional electro-optical material have been also studied. The introduction of Eu^3＋ distinctly increased the Curie temperature （Tc） of NBT-xEu^3＋ ceramics from 640℃ to 711℃ as x ranges from 0 to 0.40. For higher temperature applications, the electrical conductivity was also investigated. The conduction of charge carriers in hightemperature range originates from the conducting electrons from the ionization of oxygen vacancies. High Tc and low tanδ makes Eu^3＋-doped NBT ceramic also suitable for high temperature piezoelectric sensor applications and electro-optical integration.
基金financially supported by National Natural Science Foundation of China(61671224)and Science Foundation of Jiangxi Provincial Education Department of China(GJJ160919)the“Bairen Yuanhang”Project funding supported by Jiangxi Science and Technology Association.
文摘Ce and W co-doped CaBi_(2)Nb_(2)O_(9) ceramics with chemical formula Ca_(0.96)Ce_(0.04)Bi_(2)Nb_(2-x)W_(x)O_(9)(CCBNW100x,x=0-0.07)are fabricated via conventional solid state sintering method,to investigate the effect of W addition on the structure,electrical resistivity,dielectric and piezoelectric properties.A piezoelectric constant d33 of 13.4 pC/N is obtained in CCBN-W2 ceramics,>100% higher than that of pure CaBi_(2)Nb_(2)O_(9)(d_(33)=5.8e6.4 pC/N).Of particular significance is that the electrical resistivity of CCBN-W2 ceramics(r=3.7×109 U cm at 500℃)is three orders of magnitude higher than pure CaBi_(2)Nb_(2)O_(9)(r=2.9×10^(6) U cm at same temperature).All these properties,together with its low dielectric loss(tandδ0.13%)and excellent d33 thermal stability up to 800℃,merit the CCBN-W2 ceramics for high temperature piezoelectric sensing applications.
基金supported by National Basic Research Program of China (No. 2016YFB0700502) National Natural Science Foundation of China (No. 51372024)
文摘Bi_4Ti_3O_(12) is an important lead-free ferroelectric material.Doping modification of Bi_4Ti_3O_(12)has attracted great attention to improving its performances.In this work,the effect of Sr dopants on the microstructure,dielectric,and conductivity of Bi_4Ti_3O_(12) ceramic was investigated by XRD,SEM,and AC impedance spectroscopy.Substitution of 1 at%Sr for Bi decreased the grain size,suppressed the dielectric dispersion of Bi_4Ti_3O_(12) ceramic at room temperature,and resulted in different effects on the conductivity of grains and grain boundaries.The conductivity of grains in Bi_4Ti_3O_(12) ceramic was increased by the small amount of Sr dopants in the whole experimental temperature range.While the grain boundaries of 1 at%Sr-doped Bi_4Ti_3O_(12) exhibited lower conductivity than pure Bi_4Ti_3O_(12) below～380℃and higher conductivity above～380℃.The experimental phenomena were interpreted in term of compensating defects for Sr dopants.
基金This work is supported by the U.S.Office of Naval Research(ONR,N00014-20-1-2600)The high-resolution TEM/STEM characterization at Purdue University is supported by the U.S.National Science Foundation(Nos.DMR-1565822 and DMR-2016453)。
文摘A new vertically aligned nanocomposite(VAN)structure based on two-dimensional(2D)layered oxides has been designed and self-assembled on both LaAlO_(3)(001)and SrTiO3(001)substrates.The new VAN structure consists of epitaxially grown Co_(3)O_(4) nanopillars embedded in the Bi_(2)WO_(6) matrix with a unique 2D layered structure,as evidenced by the microstructural analysis.Physical property measurements show that the new Bi_(2)WO_(6)-Co_(3)O_(4) VAN structure exhibits strong ferromagnetic and piezoelectric response at room temperature as well as anisotropic permittivity response.This work demonstrates a new approach in processing multifunctional VANs structure based on the layered oxide systems towards future nonlinear optics,ferromagnets,and multiferroics.
基金the Third World Academy of Sciences(RG/PHYS/LA Nos.99-050,02-225 and 05-043)to the ICTP,Trieste-Italy,for financial support of Latin-American Network of Ferroelectric Materials(NET-43,currently NT-02).
文摘The paper presents the structural and ferroelectric results for Sr_(1-x)Ba_(x)Bi_(2)Nb_(2)O_(9)(x=0.30;0.85)thin films,which were obtained by using dip-coating.The solutions containing the desirable ions were prepared from the powders of the previous studied ceramic samples.The films were deposited at room temperature on Fluorine-doped Tin Oxide(FTO)substrates and submitted to a heat treatment for crystallization.The films were characterized by using scanning microscopy electronic,energy dispersive spectroscopy and ellipsometry.Hysteresis ferroelectric loops were obtained,at room temperature,by using a Sawyer-Tower circuit at several frequencies.A well-defined grain structure was observed for both compositions.The energy dispersive spectroscopy(EDS)measurements revealed the presence of the corresponding elements from the chemical composition of the ceramic systems.The band-gap energy was around 3.3 eV for both samples.Typical hysteresis loops for normal and relaxor ferroelectrics were obtained for x=0.30 and 0.85,respectively.
