The behuviour of B atoms added to mono-and poly-crystalline Ni_3AI alloys has been investi- gated hy positron annihilation technique(PA T).If the additive of B was less than 1.37 at-%, some of B atoms solid-solutioned...The behuviour of B atoms added to mono-and poly-crystalline Ni_3AI alloys has been investi- gated hy positron annihilation technique(PA T).If the additive of B was less than 1.37 at-%, some of B atoms solid-solutioned interstitially into matrix and distorted the lattice,thus the lifetime (τ) of positron (e^+) Or matrix dilated:the others of them segregated on vacancy-like defects and formed "filling effect",thus the mean lifetime (τ)and S parameters decreased.If B added was increased up to 2.22 at-%,more defects having larger free volume were induced by horide eutectic occurred along grain boundaries and grain interior,thus the τ in vacancy-like defects.τ and S parameters increased remarkably.展开更多
Pervoskite-type oxides LaFe_ 1-yCu_yO_3 was prepared by citrate method. Using a fluorescent Hg lamp as irradiator, the degradation experiments of acid red 3B were carried out in the suspension system of LaFe_ 1-yCu_yO...Pervoskite-type oxides LaFe_ 1-yCu_yO_3 was prepared by citrate method. Using a fluorescent Hg lamp as irradiator, the degradation experiments of acid red 3B were carried out in the suspension system of LaFe_ 1-yCu_yO_3. The results show that the doped oxides LaFe_ 1-yCu_yO_3 have good photocatalytic oxidation property. With the study of positron annihilation, its photocatalytic activity is mainly related with defect structures resulted by doping.展开更多
采用高温固相法合成了系列单相Ca(1-x-y)A l2O4∶Eux2+,Ndy3+(0≤x≤0.045,0≤y≤0.0037)粉末样品,并表征了其发光特性.研究结果表明,样品的发射光谱为最大发射峰位于440 nm的宽带谱,属于Eu2+的4f65d→4f7跃迁.通过对Eu2+,Nd3+掺杂量与...采用高温固相法合成了系列单相Ca(1-x-y)A l2O4∶Eux2+,Ndy3+(0≤x≤0.045,0≤y≤0.0037)粉末样品,并表征了其发光特性.研究结果表明,样品的发射光谱为最大发射峰位于440 nm的宽带谱,属于Eu2+的4f65d→4f7跃迁.通过对Eu2+,Nd3+掺杂量与样品发光性能之间关系的研究发现,Eu2+和Nd3+最佳掺杂量分别为x=0.001 25和y=0.002 5,并且Nd3+对改善蓝色长余辉材料CaA l4∶Eu2+的余辉性能具有重要的作用.在最佳掺杂条件下,样品的余辉时间可达1 000 m in,初始亮度大于1 200 m cd/m2,60 m in后发光粉的亮度仍然在10 m cd/m2以上.利用正电子湮灭技术和热释光技术,研究了Eu2+和Nd3+对CaA l2O4∶Eu2+,Nd3+材料的发光性能的影响.展开更多
The CS/PVA/Fe_3O_4 nanocomposite membranes with chainlike arrangement of Fe_3O_4 nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship...The CS/PVA/Fe_3O_4 nanocomposite membranes with chainlike arrangement of Fe_3O_4 nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship between the microstructure of the magnetic anisotropic CS/PVA/Fe_3O_4 membrane and the evolved macroscopic physicochemical property. With the same doping content, the relative crystallinity of CS/PVA/Fe_3O_4-M is lower than that of CS/PVA/Fe_3O_4.The Fourier transform infrared spectroscopy（FT-TR） measurements indicate that there is no chemical bonding between polymer molecule and Fe_3O_4 nanoparticle. The Fe_3O_4 nanoparticles in CS/PVA/Fe_3O_4 and CS/PVA/Fe_3O_4-M are wrapped by the chains of CS/PVA, which is also confirmed by scanning electron microscopy（SEM） and x-ray diffraction（XRD）analysis. The saturation magnetization value of CS/PVA/Fe_3O_4-M obviously increases compared with that of non-magnetic aligned membrane, meanwhile the transmittance decreases in the UV-visible region. The o-Ps lifetime distribution provides information about the free-volume nanoholes present in the amorphous region. It is suggested that the microstructure of CS/PVA/Fe_3O_4 membrane can be modified in its curing process under a magnetic field, which could affect the magnetic properties and the transmittance of nanocomposite membrane. In brief, a full understanding of the relationship between the microstructure and the macroscopic property of CS/PVA/Fe_3O_4 nanocomposite plays a vital role in exploring and designing the novel multifunctional materials.展开更多
Information of defects and 3d electrons in transition metals (Ti,V,Cu) and TiAl-based alloys (Ti50Al50,Ti50Al48V2,Ti50Al48Cu2) can be extracted from the positron lifetime and coincidence Doppler broadening spectra. Th...Information of defects and 3d electrons in transition metals (Ti,V,Cu) and TiAl-based alloys (Ti50Al50,Ti50Al48V2,Ti50Al48Cu2) can be extracted from the positron lifetime and coincidence Doppler broadening spectra. The results show that the 3d electron signals for the transition metals Ti,V and Cu increase with the number of 3d electrons. The 3d electron signal and the electron density for binary TiAl alloy are relatively low due to the (Ti)3d-(Al)3p interactions. The addition of V and Cu atoms to TiAl alloy leads to the increase in the electron densities in bulk and the defects on grain boundaries simultaneously,as well as the enhancement of the 3d electron signal. The 3d electron signal in the spectrum of Ti50Al48Cu2 alloy is higher than that of Ti50Al48V2 alloy.展开更多
The results of a series of experiments on 3-photon annihilation of positrons and electrons, including the energy-angular correlation, angular distribution, energy spectrum and linear polarization of the annihilation p...The results of a series of experiments on 3-photon annihilation of positrons and electrons, including the energy-angular correlation, angular distribution, energy spectrum and linear polarization of the annihilation photons, the method of measuring the intensities of 3-photon annihilation, and the upper limit of axion production in the triplet positronium decay, are reported.展开更多
SrTi1-xFexO3-δ ceramics were prepared using a traditional solid-state reaction method. From X-ray diffraction(XRD) result, we found that the doped Fe^3+ dissolved in the lattice, and no secondary phase was observed. ...SrTi1-xFexO3-δ ceramics were prepared using a traditional solid-state reaction method. From X-ray diffraction(XRD) result, we found that the doped Fe^3+ dissolved in the lattice, and no secondary phase was observed. Cation vacancies in perovskite oxides were identified via positron annihilation lifetime spectroscopy(PALS) measurements. Undoped and Fe-doped SrTiO3 ceramics and single-crystal SrTiO3 were measured by PALS at room temperature. The results show that the main defects in undoped SrTiO3 ceramics are Ti-related defects, and the isolated Ti vacancy lifetime is about 183.4 ps. With the increase of Fe^3+, the concentration of the Ti vacancies decreases accompanied by the appearance of the V^nSr-nV^**O(defect association of Sr vacancies and multiple O vacancies) vacancy defect complexes.展开更多
3D direct-writing via photopolymerization based on two-photon absorption(TPA) can achieve excellent out-of-plane resolution.The key to this technology is a quadratic intensity dependence in photoexciting the TPA photo...3D direct-writing via photopolymerization based on two-photon absorption(TPA) can achieve excellent out-of-plane resolution.The key to this technology is a quadratic intensity dependence in photoexciting the TPA photosensitizers. Triplet-triplet annihilation(TTA) also has similar nonlinear light-intensity dependence. As a result, TTA can also generate spatially confined excitation near the beam focus. Combining the photopolymerization reaction with the TTA system composed of palladium porphyrin and diphenylanthracene, 3D direct-writing micro-fabrication based on photopolymerization and the TTAwas realized.The out-of-plane resolution can reach 10 μm under continuous-wave laser excitation. TTA-based 3D direct-writing technology does not need an expensive femtosecond pulsed laser, showing the potential of a next-generation 3D printing technology.展开更多
The defects, the behavior of 3d electrons and the hyperfine interactions in binary Fe-Al alloys with different Al contents have been studied by measurements of positron lifetime spectra, coincidence Doppler broadening...The defects, the behavior of 3d electrons and the hyperfine interactions in binary Fe-Al alloys with different Al contents have been studied by measurements of positron lifetime spectra, coincidence Doppler broadening spectra of positron annihilation radiation and M？ssbauer spectra. The results show that on increasing the Al content in Fe-Al alloys, the mean positron lifetime of the alloys increase, while the mean electron density of the alloys decrease. The increase of Al content in binary Fe-Al alloys will decrease the amount of unpaired 3d electrons; as a consequence the probability of positron annihilation with 3d electrons and the hyperfine field decrease rapidly. M？ssbauer spectra of binary Fe-Al alloys with Al content less than 25 at.% show discrete sextets and these alloys make a ferromagnetic contribution at room temperature. The M？ssbauer spectrum of Fe70Al30 shows a broad singlet. As Al content higher than 40 at.%, the M？ssbauer spectra of these alloys are singlet, that is, the alloys are paramagnetic. The behavior of a 3d electron and its effect on the hyperfine field of the binary Fe-Al alloy has been discussed.展开更多
Co^2＋/γ-Al2O3 samples were prepared by incipient wetness impregnation of γ-Al2O3 with different concentration solution of COCl2 and dried at 40 ℃. We measured the positron lifetime spectra of the samples of differ...Co^2＋/γ-Al2O3 samples were prepared by incipient wetness impregnation of γ-Al2O3 with different concentration solution of COCl2 and dried at 40 ℃. We measured the positron lifetime spectra of the samples of different Co2＋ mass fractions （0%-8.24%） heated at different temperatures （100 -500 ℃）. All lifetime spectra were resolved into four components, in which the third and the fourth components were related to the surface state of the micropores and the secondary pores of the γ-Al2O3. The experimental results showed that the Co^2＋ was mainly located in the micropores and the secondary pores near to the exterior of the support. For low Co^2＋ mass fraction samples, when the heating temperature was above 400℃, dispersal was almost finished. When the Co^2＋ mass fraction was above 5.59%, Co^2＋ and Cl were dispersed into the secondary pores in the form of multiple layers.展开更多
文摘The behuviour of B atoms added to mono-and poly-crystalline Ni_3AI alloys has been investi- gated hy positron annihilation technique(PA T).If the additive of B was less than 1.37 at-%, some of B atoms solid-solutioned interstitially into matrix and distorted the lattice,thus the lifetime (τ) of positron (e^+) Or matrix dilated:the others of them segregated on vacancy-like defects and formed "filling effect",thus the mean lifetime (τ)and S parameters decreased.If B added was increased up to 2.22 at-%,more defects having larger free volume were induced by horide eutectic occurred along grain boundaries and grain interior,thus the τ in vacancy-like defects.τ and S parameters increased remarkably.
文摘Pervoskite-type oxides LaFe_ 1-yCu_yO_3 was prepared by citrate method. Using a fluorescent Hg lamp as irradiator, the degradation experiments of acid red 3B were carried out in the suspension system of LaFe_ 1-yCu_yO_3. The results show that the doped oxides LaFe_ 1-yCu_yO_3 have good photocatalytic oxidation property. With the study of positron annihilation, its photocatalytic activity is mainly related with defect structures resulted by doping.
文摘采用高温固相法合成了系列单相Ca(1-x-y)A l2O4∶Eux2+,Ndy3+(0≤x≤0.045,0≤y≤0.0037)粉末样品,并表征了其发光特性.研究结果表明,样品的发射光谱为最大发射峰位于440 nm的宽带谱,属于Eu2+的4f65d→4f7跃迁.通过对Eu2+,Nd3+掺杂量与样品发光性能之间关系的研究发现,Eu2+和Nd3+最佳掺杂量分别为x=0.001 25和y=0.002 5,并且Nd3+对改善蓝色长余辉材料CaA l4∶Eu2+的余辉性能具有重要的作用.在最佳掺杂条件下,样品的余辉时间可达1 000 m in,初始亮度大于1 200 m cd/m2,60 m in后发光粉的亮度仍然在10 m cd/m2以上.利用正电子湮灭技术和热释光技术,研究了Eu2+和Nd3+对CaA l2O4∶Eu2+,Nd3+材料的发光性能的影响.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11475197,11575205,11404100,and 11304083)the Key Scientific and Technological Project of Henan Province,China(Grant No.102102210186)
文摘The CS/PVA/Fe_3O_4 nanocomposite membranes with chainlike arrangement of Fe_3O_4 nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship between the microstructure of the magnetic anisotropic CS/PVA/Fe_3O_4 membrane and the evolved macroscopic physicochemical property. With the same doping content, the relative crystallinity of CS/PVA/Fe_3O_4-M is lower than that of CS/PVA/Fe_3O_4.The Fourier transform infrared spectroscopy（FT-TR） measurements indicate that there is no chemical bonding between polymer molecule and Fe_3O_4 nanoparticle. The Fe_3O_4 nanoparticles in CS/PVA/Fe_3O_4 and CS/PVA/Fe_3O_4-M are wrapped by the chains of CS/PVA, which is also confirmed by scanning electron microscopy（SEM） and x-ray diffraction（XRD）analysis. The saturation magnetization value of CS/PVA/Fe_3O_4-M obviously increases compared with that of non-magnetic aligned membrane, meanwhile the transmittance decreases in the UV-visible region. The o-Ps lifetime distribution provides information about the free-volume nanoholes present in the amorphous region. It is suggested that the microstructure of CS/PVA/Fe_3O_4 membrane can be modified in its curing process under a magnetic field, which could affect the magnetic properties and the transmittance of nanocomposite membrane. In brief, a full understanding of the relationship between the microstructure and the macroscopic property of CS/PVA/Fe_3O_4 nanocomposite plays a vital role in exploring and designing the novel multifunctional materials.
基金the National Natural Science Foundation of China (Grant No 50361002)Guangxi University Key Program for Science and Technology Research (Grant No 2003ZD04)the Natural Science Foundation of Guangxi Province (Grant No 0480004)
文摘Information of defects and 3d electrons in transition metals (Ti,V,Cu) and TiAl-based alloys (Ti50Al50,Ti50Al48V2,Ti50Al48Cu2) can be extracted from the positron lifetime and coincidence Doppler broadening spectra. The results show that the 3d electron signals for the transition metals Ti,V and Cu increase with the number of 3d electrons. The 3d electron signal and the electron density for binary TiAl alloy are relatively low due to the (Ti)3d-(Al)3p interactions. The addition of V and Cu atoms to TiAl alloy leads to the increase in the electron densities in bulk and the defects on grain boundaries simultaneously,as well as the enhancement of the 3d electron signal. The 3d electron signal in the spectrum of Ti50Al48Cu2 alloy is higher than that of Ti50Al48V2 alloy.
文摘The results of a series of experiments on 3-photon annihilation of positrons and electrons, including the energy-angular correlation, angular distribution, energy spectrum and linear polarization of the annihilation photons, the method of measuring the intensities of 3-photon annihilation, and the upper limit of axion production in the triplet positronium decay, are reported.
基金Supported by the National Natural Science Foundation of China(11575129,11275142)
文摘SrTi1-xFexO3-δ ceramics were prepared using a traditional solid-state reaction method. From X-ray diffraction(XRD) result, we found that the doped Fe^3+ dissolved in the lattice, and no secondary phase was observed. Cation vacancies in perovskite oxides were identified via positron annihilation lifetime spectroscopy(PALS) measurements. Undoped and Fe-doped SrTiO3 ceramics and single-crystal SrTiO3 were measured by PALS at room temperature. The results show that the main defects in undoped SrTiO3 ceramics are Ti-related defects, and the isolated Ti vacancy lifetime is about 183.4 ps. With the increase of Fe^3+, the concentration of the Ti vacancies decreases accompanied by the appearance of the V^nSr-nV^**O(defect association of Sr vacancies and multiple O vacancies) vacancy defect complexes.
基金supported by the National Key R&D Program of China (2021YFA1502500)the National Natural Science Foundation of China (22125502 and 22071207)。
文摘3D direct-writing via photopolymerization based on two-photon absorption(TPA) can achieve excellent out-of-plane resolution.The key to this technology is a quadratic intensity dependence in photoexciting the TPA photosensitizers. Triplet-triplet annihilation(TTA) also has similar nonlinear light-intensity dependence. As a result, TTA can also generate spatially confined excitation near the beam focus. Combining the photopolymerization reaction with the TTA system composed of palladium porphyrin and diphenylanthracene, 3D direct-writing micro-fabrication based on photopolymerization and the TTAwas realized.The out-of-plane resolution can reach 10 μm under continuous-wave laser excitation. TTA-based 3D direct-writing technology does not need an expensive femtosecond pulsed laser, showing the potential of a next-generation 3D printing technology.
基金Supported by National Natural Science Foundation of China(10764001,51061002)Program for Science and Technology Innovation Team of Guangxi University
文摘The defects, the behavior of 3d electrons and the hyperfine interactions in binary Fe-Al alloys with different Al contents have been studied by measurements of positron lifetime spectra, coincidence Doppler broadening spectra of positron annihilation radiation and M？ssbauer spectra. The results show that on increasing the Al content in Fe-Al alloys, the mean positron lifetime of the alloys increase, while the mean electron density of the alloys decrease. The increase of Al content in binary Fe-Al alloys will decrease the amount of unpaired 3d electrons; as a consequence the probability of positron annihilation with 3d electrons and the hyperfine field decrease rapidly. M？ssbauer spectra of binary Fe-Al alloys with Al content less than 25 at.% show discrete sextets and these alloys make a ferromagnetic contribution at room temperature. The M？ssbauer spectrum of Fe70Al30 shows a broad singlet. As Al content higher than 40 at.%, the M？ssbauer spectra of these alloys are singlet, that is, the alloys are paramagnetic. The behavior of a 3d electron and its effect on the hyperfine field of the binary Fe-Al alloy has been discussed.
基金Supported by the National Natural Science Foundation of China ( 10675093)
文摘Co^2＋/γ-Al2O3 samples were prepared by incipient wetness impregnation of γ-Al2O3 with different concentration solution of COCl2 and dried at 40 ℃. We measured the positron lifetime spectra of the samples of different Co2＋ mass fractions （0%-8.24%） heated at different temperatures （100 -500 ℃）. All lifetime spectra were resolved into four components, in which the third and the fourth components were related to the surface state of the micropores and the secondary pores of the γ-Al2O3. The experimental results showed that the Co^2＋ was mainly located in the micropores and the secondary pores near to the exterior of the support. For low Co^2＋ mass fraction samples, when the heating temperature was above 400℃, dispersal was almost finished. When the Co^2＋ mass fraction was above 5.59%, Co^2＋ and Cl were dispersed into the secondary pores in the form of multiple layers.
