SrBi4Ti4O15 powder was synthesized by conventional solid state synthesis （ CS ） and molten salt synthesis （ MSS ） . MSS method can synthesize plate-like SrBi4Ti4O15 at lower temperature （900℃） than CS method. P...SrBi4Ti4O15 powder was synthesized by conventional solid state synthesis （ CS ） and molten salt synthesis （ MSS ） . MSS method can synthesize plate-like SrBi4Ti4O15 at lower temperature （900℃） than CS method. Plate-like form becomes more distinct when the synthesis temperature increases. This would help cause the grain orientation of the ceramics after sintering. The sintered samples of MSS had grain orientation at （0,0, 10） plane. The degree of （0,0,10） grain orientation F was 62.1% . Hot pressing made （0,0,10） grain orientation more distinct （ F = 85.7% ）. The microstructures of the sintered samples were detected by SEM. Due to the grain orientation the density of samples fabricated by MSS was lower than that of prepared by CS.展开更多
Lanthanum doped bismuth layer structured ferroelectrics （BLSFs） Ca1 - x LaxBi4 （Ti0.9W0. 1 ）4O15 （ x = 0, 0.2, 0.3, 0.4, 0.6） ceramics were prepared by solid-state reaction method. X-ray diffraction （XRD） patt...Lanthanum doped bismuth layer structured ferroelectrics （BLSFs） Ca1 - x LaxBi4 （Ti0.9W0. 1 ）4O15 （ x = 0, 0.2, 0.3, 0.4, 0.6） ceramics were prepared by solid-state reaction method. X-ray diffraction （XRD） patterns showed that single phase was formed when x = 0 - 0.6. The effects of La^3＋ doping on dielectric, piezoelectric and ferroelectric properties of Ca1-xLaxBi4（Ti0.9W0.1）4O15 ceramics were studied. Ca0.7La0.3Bi4（Ti0.9W0.1）4O15 ceramic had optimal properties, its dielectric constant was 166.85, dielectric loss was 0.0063, piezoelectric strain constant was 11 pc·N^-1, remanent polarization was 18.1μC·cm^-2 and coercive field was 118 kV·cm^-1. SEM micrographs showed that the grains of CaBi4Ti4O15-based ceramics were plate-like. The results of energy spectrum analysis （EDS） showed that La^3＋ incorporation could increase Bi/Ca ratio.展开更多
The development of stable and efficient visible light-absorbing oxide-based semiconductor photocatalysts is a desirable task for solar water splitting applications.Recently,we proposed that the low photocurrent densit...The development of stable and efficient visible light-absorbing oxide-based semiconductor photocatalysts is a desirable task for solar water splitting applications.Recently,we proposed that the low photocurrent density in film-based BiFeO_(3)(BFO)is due to charge recombination at the interface of the domain walls,which could be largely reduced in particulate photocatalyst systems.To demonstrate this hypothesis,in this work we synthesized particulate BFO and Mn-doped BiFeO_(3)(Mn-BFO)by the sol-gel method.Photocatalytic water oxidation tests showed that pure BFO had an intrinsic photocatalytic oxygen evolution reaction(OER)activity of 70μmol h^(-1) g^(-1),while BFO-2,with an optimum amount of Mn doping(0.05%),showed an OER activity of 255μmol h^(-1) g^(-1) under visible light(λ≥420 nm)irradiation.The bandgap of Mn-doped BFO could be reduced from 2.1 to 1.36 eV by varying the amount of Mn doping.Density functional theory(DFT)calculations suggested that surface Fe(rather than Mn)species serve as the active sites for water oxidation,because the overpotential for water oxidation on Fe species after Mn doping is 0.51 V,which is the lowest value measured for the different Fe and Mn species examined in this study.The improved photocatalytic water oxidation activity of Mn-BFO is ascribed to the synergistic effect of the bandgap narrowing,which increases the absorption of visible light,reduces the activation energy of water oxidation,and inhibits the recombination of photogenerated charges.This work demonstrates that Mn doping is an effective strategy to enhance the intrinsic photocatalytic water oxidation activity of particulate ferroelectric BFO photocatalysts.展开更多
La/Mn co-doped Bi4Ti3O12 ceramics, Bi3.25La0.75Ti3-xMnxO12 （x = 0.02, 0.04, 0.06, 0.08）, were prepared by the solid-state reaction method. The influence of manganese substitution for the titanium part in Bi3.25La0.7...La/Mn co-doped Bi4Ti3O12 ceramics, Bi3.25La0.75Ti3-xMnxO12 （x = 0.02, 0.04, 0.06, 0.08）, were prepared by the solid-state reaction method. The influence of manganese substitution for the titanium part in Bi3.25La0.75Ti3O12 on the sintering behaviour, microstructure, Raman spectra and electrical properties was investigated. The experimental results show that the phase composition of all samples with and without manganese doping, sintered at 1000 ℃, consists of a single phase with a bismuth-layered structure belonging to the crystalline phase Bi4Ti3O12. There is no evidence of any impurity phase, but a small change in crystallographic orientation is observed. The Curie temperature of Bi3.25La0.75Ti3-xMnxO12 ceramics is steadily shifted to lower temperature with increasing Mn-doping content. Moreover, the remnant polarisation （Pr） of Bi3.25La0.75Ti3- xMnxO12 samples increases with Mn-doping content, and the Bi3.25La0.75Ti2.92Mn0.08O12 sample exhibits the largest Pr of 16.6 μC/cm^2.展开更多
The ferroelectric response of bismuth titanate Bi4Ti3O12 （BIT） thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with thr...The ferroelectric response of bismuth titanate Bi4Ti3O12 （BIT） thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with three terms： the electric field applied in the z direction, the nearest dipole-dipole interaction in the transversal （x-y） direction, and the nearest dipole-dipole interaction in the direction perpendicular to the thin film （the z axis）. In the sample construction, we take into consideration the dipole orientations of the monoclinic and orthorhombic structures that can appear in BIT at low temperature in the ferroelectric state. The effects of temperature, stress, and the concentration of pinned dipole defects are assessed by using the hysteresis loops. The results indicate the changes in the hysteresis area with temperature and stress, and the asymmetric hysteresis loops exhibit evidence of the imprint failure mechanism with the emergence of pinned dipolar defects. The simulated shift in the hysteresis loops conforms to the experimental ferroelectric response.展开更多
SrBi 4 Ti 4O 15 ceramics samples with different Bi content of which mole radio, n (Sr): n (Bi): n (Ti):,is 1:4(1+x):4(x=-0.05,0,0.05,0.10,0.15,0.20),are prepared by solid-state reaction method.Their structure is analy...SrBi 4 Ti 4O 15 ceramics samples with different Bi content of which mole radio, n (Sr): n (Bi): n (Ti):,is 1:4(1+x):4(x=-0.05,0,0.05,0.10,0.15,0.20),are prepared by solid-state reaction method.Their structure is analyzed by X-ray diffraction,and their dielectricity and ferroelectricity are measured.Results show that pure SrBi 4 Ti 4O 15 pahase exists in the samples whith x=0.05 and 0.10.The sintered ceramics with x=0.05 have good ferroelectric and dielectric properties:The remnant polarization (2 P r) and coercive field ( E c) are 2.86×10 -9 C·m -2 and 8.65×10 6V·m -1 .The dielectric constant (ε r) changes litter in the range from 1 kHz to 4MHz,and ε r is 425 at the frequency of 1 MHz.展开更多
文摘SrBi4Ti4O15 powder was synthesized by conventional solid state synthesis （ CS ） and molten salt synthesis （ MSS ） . MSS method can synthesize plate-like SrBi4Ti4O15 at lower temperature （900℃） than CS method. Plate-like form becomes more distinct when the synthesis temperature increases. This would help cause the grain orientation of the ceramics after sintering. The sintered samples of MSS had grain orientation at （0,0, 10） plane. The degree of （0,0,10） grain orientation F was 62.1% . Hot pressing made （0,0,10） grain orientation more distinct （ F = 85.7% ）. The microstructures of the sintered samples were detected by SEM. Due to the grain orientation the density of samples fabricated by MSS was lower than that of prepared by CS.
文摘Lanthanum doped bismuth layer structured ferroelectrics （BLSFs） Ca1 - x LaxBi4 （Ti0.9W0. 1 ）4O15 （ x = 0, 0.2, 0.3, 0.4, 0.6） ceramics were prepared by solid-state reaction method. X-ray diffraction （XRD） patterns showed that single phase was formed when x = 0 - 0.6. The effects of La^3＋ doping on dielectric, piezoelectric and ferroelectric properties of Ca1-xLaxBi4（Ti0.9W0.1）4O15 ceramics were studied. Ca0.7La0.3Bi4（Ti0.9W0.1）4O15 ceramic had optimal properties, its dielectric constant was 166.85, dielectric loss was 0.0063, piezoelectric strain constant was 11 pc·N^-1, remanent polarization was 18.1μC·cm^-2 and coercive field was 118 kV·cm^-1. SEM micrographs showed that the grains of CaBi4Ti4O15-based ceramics were plate-like. The results of energy spectrum analysis （EDS） showed that La^3＋ incorporation could increase Bi/Ca ratio.
文摘The development of stable and efficient visible light-absorbing oxide-based semiconductor photocatalysts is a desirable task for solar water splitting applications.Recently,we proposed that the low photocurrent density in film-based BiFeO_(3)(BFO)is due to charge recombination at the interface of the domain walls,which could be largely reduced in particulate photocatalyst systems.To demonstrate this hypothesis,in this work we synthesized particulate BFO and Mn-doped BiFeO_(3)(Mn-BFO)by the sol-gel method.Photocatalytic water oxidation tests showed that pure BFO had an intrinsic photocatalytic oxygen evolution reaction(OER)activity of 70μmol h^(-1) g^(-1),while BFO-2,with an optimum amount of Mn doping(0.05%),showed an OER activity of 255μmol h^(-1) g^(-1) under visible light(λ≥420 nm)irradiation.The bandgap of Mn-doped BFO could be reduced from 2.1 to 1.36 eV by varying the amount of Mn doping.Density functional theory(DFT)calculations suggested that surface Fe(rather than Mn)species serve as the active sites for water oxidation,because the overpotential for water oxidation on Fe species after Mn doping is 0.51 V,which is the lowest value measured for the different Fe and Mn species examined in this study.The improved photocatalytic water oxidation activity of Mn-BFO is ascribed to the synergistic effect of the bandgap narrowing,which increases the absorption of visible light,reduces the activation energy of water oxidation,and inhibits the recombination of photogenerated charges.This work demonstrates that Mn doping is an effective strategy to enhance the intrinsic photocatalytic water oxidation activity of particulate ferroelectric BFO photocatalysts.
基金Project supported by the National Science Fund for Distinguished Young Scholars (Grant No. 50625204)National Natural Science Fund for Creative Research Groups (Grant No. 50621201)+2 种基金the Ministry of Science and Technology of China through National Basic Research Program of China (Grant No. 2009CB623301)through National High Technology ResearchDevelopment Program of China (Grant No. 2006AA03Z428)
文摘La/Mn co-doped Bi4Ti3O12 ceramics, Bi3.25La0.75Ti3-xMnxO12 （x = 0.02, 0.04, 0.06, 0.08）, were prepared by the solid-state reaction method. The influence of manganese substitution for the titanium part in Bi3.25La0.75Ti3O12 on the sintering behaviour, microstructure, Raman spectra and electrical properties was investigated. The experimental results show that the phase composition of all samples with and without manganese doping, sintered at 1000 ℃, consists of a single phase with a bismuth-layered structure belonging to the crystalline phase Bi4Ti3O12. There is no evidence of any impurity phase, but a small change in crystallographic orientation is observed. The Curie temperature of Bi3.25La0.75Ti3-xMnxO12 ceramics is steadily shifted to lower temperature with increasing Mn-doping content. Moreover, the remnant polarisation （Pr） of Bi3.25La0.75Ti3- xMnxO12 samples increases with Mn-doping content, and the Bi3.25La0.75Ti2.92Mn0.08O12 sample exhibits the largest Pr of 16.6 μC/cm^2.
基金sponsored by the research departments of the Universidad Nacional de Colombia DIMA and DIB under Project 201010018227-"Crecimientoy caracterización eléctrica y estructural de películas delgadas de BixTiyOz producidas mediante Magnetrón Sputtering"Project 12920-"Desarrollo teóricoexperimental de nanoestructuras basadas en Bismutoy materiales similares""Bisnano Project"
文摘The ferroelectric response of bismuth titanate Bi4Ti3O12 （BIT） thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with three terms： the electric field applied in the z direction, the nearest dipole-dipole interaction in the transversal （x-y） direction, and the nearest dipole-dipole interaction in the direction perpendicular to the thin film （the z axis）. In the sample construction, we take into consideration the dipole orientations of the monoclinic and orthorhombic structures that can appear in BIT at low temperature in the ferroelectric state. The effects of temperature, stress, and the concentration of pinned dipole defects are assessed by using the hysteresis loops. The results indicate the changes in the hysteresis area with temperature and stress, and the asymmetric hysteresis loops exhibit evidence of the imprint failure mechanism with the emergence of pinned dipolar defects. The simulated shift in the hysteresis loops conforms to the experimental ferroelectric response.
文摘SrBi 4 Ti 4O 15 ceramics samples with different Bi content of which mole radio, n (Sr): n (Bi): n (Ti):,is 1:4(1+x):4(x=-0.05,0,0.05,0.10,0.15,0.20),are prepared by solid-state reaction method.Their structure is analyzed by X-ray diffraction,and their dielectricity and ferroelectricity are measured.Results show that pure SrBi 4 Ti 4O 15 pahase exists in the samples whith x=0.05 and 0.10.The sintered ceramics with x=0.05 have good ferroelectric and dielectric properties:The remnant polarization (2 P r) and coercive field ( E c) are 2.86×10 -9 C·m -2 and 8.65×10 6V·m -1 .The dielectric constant (ε r) changes litter in the range from 1 kHz to 4MHz,and ε r is 425 at the frequency of 1 MHz.
