The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission fr...The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.展开更多
The room temperature stabled monoclinic KNbO3 nanowires were found to act as photocatalyst for photocatalytic methane production and dye degradation in this work. Higher activities have been observed for monoclinic ph...The room temperature stabled monoclinic KNbO3 nanowires were found to act as photocatalyst for photocatalytic methane production and dye degradation in this work. Higher activities have been observed for monoclinic phase compared to the reference（orthorhombic phase）. In the photoreduction of CO2 reaction, the monoclinic KNbO3 nanowires exhibited a CH4 evolution rate of 0.025 μmol·g-1·h-1, which was higher than 0.021 μmol·g-1·h-1 of orthorhombic KNbO3 nanowires. In the photodegradation of rhodamine B（Rh B）, almost all the Rh B were degraded after 90 min light illumination for monoclinic KNbO3 nanowires. But for orthorhombic KNbO3 nanowires, the concentration of Rh B only decreased to 62% of the initial value.展开更多
A new phase of Gd_(2-x)Na_xCuO_4 was synthesized by direct precipitation from the mixture of Gd_2O_3 and CuO in the molten KOH/NaOH/KNO_3 solution at temperature as low as 280℃. The resulting precipitate was characte...A new phase of Gd_(2-x)Na_xCuO_4 was synthesized by direct precipitation from the mixture of Gd_2O_3 and CuO in the molten KOH/NaOH/KNO_3 solution at temperature as low as 280℃. The resulting precipitate was characterized by using SEM, XRD, EDX, XPS and magnetic method. The XRD data indicate that the precipitated Gd_(2-x)Na_xCuO_4 is monoclinic with lattice parameters a=8.6816, b=3.7233. c=6.0796. a=γ=90', 0=108.75° and V=186. 13.展开更多
La(Nb_(0.9)V0.1)O_(4)has been shown by in situ Raman spectroscopy and X-ray diffraction to undergo a ferroelastic phase transition from monoclinic fergusonite to tetragonal scheelite(T_(M–T))at 350°C,accompanied...La(Nb_(0.9)V0.1)O_(4)has been shown by in situ Raman spectroscopy and X-ray diffraction to undergo a ferroelastic phase transition from monoclinic fergusonite to tetragonal scheelite(T_(M–T))at 350°C,accompanied by 3.55%spontaneous strain and an abrupt change in the thermal expansion coefficient(α_(L))from+15.5 ppm°C^(−1)to+11._(4)ppm°C^(−1).展开更多
The piezoelectric strain of K_(0.5)Na_(0.5)NbO_(3)-based lead-free ceramic at different temperatures was studied.The Rayleigh analysis shows that the intrinsic and extrinsic contributions are increased at temperature ...The piezoelectric strain of K_(0.5)Na_(0.5)NbO_(3)-based lead-free ceramic at different temperatures was studied.The Rayleigh analysis shows that the intrinsic and extrinsic contributions are increased at temperature from 173 to 298 K.In addition,a monoclinic phase structure was observed at 83 K.The results of phase field simulation show that the temperature dependent microstructure evolution is a function of the local structure size.This work contributes to understanding the structure and properties relationship of the multi-cations doped KNN-based piezoelectric ceramics as a function of temperature.展开更多
Europium-doped bismuth vanadate EBVO-x(0≤x≤7)with different crystalline phases has been successfully synthesized via a simple one-pot hydrothermal method.X-ray diffractometry,Raman scattering and scanning electron m...Europium-doped bismuth vanadate EBVO-x(0≤x≤7)with different crystalline phases has been successfully synthesized via a simple one-pot hydrothermal method.X-ray diffractometry,Raman scattering and scanning electron microscopy revealed that the crystal phase transformed from the monoclinic phase to the tetragonal phase,probably owing to the substitution of europium ions in the Bi3+positions.Significant changes in the physical-chemical characteristics of the material with the initial molar ratio of Eu to Bi were observed.Adding the europium causes alteration of the BiVO4 structure from a monoclinic scheelite(x<3)to a tetragonal zircon(x≥3)structure with a mixed-phase state between them.The photocatalytic activities of the prepared samples were evaluated by degrading methylene blue(MB)under visible light irradiation and the best performance was attained for the EBVO-5 material with a phase transition trend.The results of the photoluminescence spectroscopy demonstrated that the recombination of photogenerated charges was greatly depressed and the photocatalytic activity was improved by the substitution of Eu for Bi in BiVO4.Furthermore,the proposed mechanism of the enhanced photocatalytic activity was discussed.展开更多
The dielectric ceramic of barium dititanate compound BaTi_(2)O_(5) had been prepared through the hydrothermal process by applying different parameters,such as pH-value,reaction time,temperature and pressure.The prepar...The dielectric ceramic of barium dititanate compound BaTi_(2)O_(5) had been prepared through the hydrothermal process by applying different parameters,such as pH-value,reaction time,temperature and pressure.The prepared powders were examined by X-ray diffraction(XRD).The predominant phase was a monoclinic phase with lattice constants(a=16:6381,b=3:555,c=9:3406Å),(β=107:47°,α=γ=90°),and the unit cell volume(527Å^(3)).The surface morphology was demonstrated by Scanning Electron Microscopy(SEM).It exhibited the grains in spherical and elliptical shapes with high homogeneity.The shapes of nanostructure were analyzed by Transmission Electron Microscopy(TEM).The appearance of nanostructures like the nanoparticles and nano rods were found.The size of nanoparticles was in the range of 9–31 nm,and size of nanorods was 32–37 nm.The dielectric measurements were done by using LCR meter at different temperature and frequencies(10,50 and 100 kHz).It was clear that the Curie temperature had a high value up to(485℃).The relative permittivity was partially changed for two prepared samples regarding high pressure and long reaction time,which were the main preparation conditions of hydrothermal method.展开更多
基金supported by the National Natural Science Foundation of China(No.91950109 and 61875109)the Natural Science Foundation of Shanxi Province(No.201901D111010(ZD))Postgraduate Education Innovation Project of Shanxi Province(No.2019SY052 and No.2020BY022)。
文摘The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.
基金supported by the National Basic Research Program of China(973 Program,2013CB632400)the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National Natural Science Foundation of China(Nos.51272102 and 21103070)
文摘The room temperature stabled monoclinic KNbO3 nanowires were found to act as photocatalyst for photocatalytic methane production and dye degradation in this work. Higher activities have been observed for monoclinic phase compared to the reference（orthorhombic phase）. In the photoreduction of CO2 reaction, the monoclinic KNbO3 nanowires exhibited a CH4 evolution rate of 0.025 μmol·g-1·h-1, which was higher than 0.021 μmol·g-1·h-1 of orthorhombic KNbO3 nanowires. In the photodegradation of rhodamine B（Rh B）, almost all the Rh B were degraded after 90 min light illumination for monoclinic KNbO3 nanowires. But for orthorhombic KNbO3 nanowires, the concentration of Rh B only decreased to 62% of the initial value.
文摘A new phase of Gd_(2-x)Na_xCuO_4 was synthesized by direct precipitation from the mixture of Gd_2O_3 and CuO in the molten KOH/NaOH/KNO_3 solution at temperature as low as 280℃. The resulting precipitate was characterized by using SEM, XRD, EDX, XPS and magnetic method. The XRD data indicate that the precipitated Gd_(2-x)Na_xCuO_4 is monoclinic with lattice parameters a=8.6816, b=3.7233. c=6.0796. a=γ=90', 0=108.75° and V=186. 13.
基金supported by the National Key Research and Development Program of China(Grant 2017YFB0406301)the Sustainability and Substitution of Functional Materials and Devices EPSRC(EP/L017s563/1)+2 种基金the National Natural Science Foundation of China(51972260,52072295)the State Key Laboratory of Electrical Insulation and Power Equipment(Grant EIPE19210)the Fundamental Research Funds for the Central University,and the 111 Project of China(B14040).
文摘La(Nb_(0.9)V0.1)O_(4)has been shown by in situ Raman spectroscopy and X-ray diffraction to undergo a ferroelastic phase transition from monoclinic fergusonite to tetragonal scheelite(T_(M–T))at 350°C,accompanied by 3.55%spontaneous strain and an abrupt change in the thermal expansion coefficient(α_(L))from+15.5 ppm°C^(−1)to+11._(4)ppm°C^(−1).
基金Founded by the National Natural Science Foundation of China (Nos.U1806221 and 51932006)the Instruction&Development Zone of Shandong Province (2018ZCQZB01 and 2019ZCQZB03)。
文摘The piezoelectric strain of K_(0.5)Na_(0.5)NbO_(3)-based lead-free ceramic at different temperatures was studied.The Rayleigh analysis shows that the intrinsic and extrinsic contributions are increased at temperature from 173 to 298 K.In addition,a monoclinic phase structure was observed at 83 K.The results of phase field simulation show that the temperature dependent microstructure evolution is a function of the local structure size.This work contributes to understanding the structure and properties relationship of the multi-cations doped KNN-based piezoelectric ceramics as a function of temperature.
基金financially supported by National Natural Science Foundation of China(51974168)Science and Technology Major Project Inner Mongolia Autonomous Region in China(2019ZD023 and 2021ZD0028)State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)(SYSJJ2020-08).
文摘Europium-doped bismuth vanadate EBVO-x(0≤x≤7)with different crystalline phases has been successfully synthesized via a simple one-pot hydrothermal method.X-ray diffractometry,Raman scattering and scanning electron microscopy revealed that the crystal phase transformed from the monoclinic phase to the tetragonal phase,probably owing to the substitution of europium ions in the Bi3+positions.Significant changes in the physical-chemical characteristics of the material with the initial molar ratio of Eu to Bi were observed.Adding the europium causes alteration of the BiVO4 structure from a monoclinic scheelite(x<3)to a tetragonal zircon(x≥3)structure with a mixed-phase state between them.The photocatalytic activities of the prepared samples were evaluated by degrading methylene blue(MB)under visible light irradiation and the best performance was attained for the EBVO-5 material with a phase transition trend.The results of the photoluminescence spectroscopy demonstrated that the recombination of photogenerated charges was greatly depressed and the photocatalytic activity was improved by the substitution of Eu for Bi in BiVO4.Furthermore,the proposed mechanism of the enhanced photocatalytic activity was discussed.
文摘The dielectric ceramic of barium dititanate compound BaTi_(2)O_(5) had been prepared through the hydrothermal process by applying different parameters,such as pH-value,reaction time,temperature and pressure.The prepared powders were examined by X-ray diffraction(XRD).The predominant phase was a monoclinic phase with lattice constants(a=16:6381,b=3:555,c=9:3406Å),(β=107:47°,α=γ=90°),and the unit cell volume(527Å^(3)).The surface morphology was demonstrated by Scanning Electron Microscopy(SEM).It exhibited the grains in spherical and elliptical shapes with high homogeneity.The shapes of nanostructure were analyzed by Transmission Electron Microscopy(TEM).The appearance of nanostructures like the nanoparticles and nano rods were found.The size of nanoparticles was in the range of 9–31 nm,and size of nanorods was 32–37 nm.The dielectric measurements were done by using LCR meter at different temperature and frequencies(10,50 and 100 kHz).It was clear that the Curie temperature had a high value up to(485℃).The relative permittivity was partially changed for two prepared samples regarding high pressure and long reaction time,which were the main preparation conditions of hydrothermal method.
