Highly pure magnesium borate （Mg2B2O5） nanowires with an average diameter of - 30 nm, an average length of 15 μm, and a high aspect ratio of - 500 have been synthesized on a large scale via a two-step method. MgBO...Highly pure magnesium borate （Mg2B2O5） nanowires with an average diameter of - 30 nm, an average length of 15 μm, and a high aspect ratio of - 500 have been synthesized on a large scale via a two-step method. MgBO2（OH） nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B205 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 ℃. The important effect of the MgBO2（OH）-Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional （1D） nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire- reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.展开更多
Giant reversible magnetocaloric effects and magnetic properties in Euo.9Ro.lTiO3 （R = La, Ce） are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitut...Giant reversible magnetocaloric effects and magnetic properties in Euo.9Ro.lTiO3 （R = La, Ce） are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitution of La （x = 0.1） and Ce （x = 0.1） ions for Eu2＋ ions. The values of -ASM and RC are evaluated to be 10.8 J/（kg.K） and 51.8 J/kg for Euo.gCeo.lTiO3 and 11 J/（kg.K） and 39.3 J/kg for Euo.9Lao.lTiO3 at a magnetic field change of I0 kOe, respectively. The large low-field enhancements of --ASM and RC can be attributed to magnetic phase transition. The giant reversible MCE and large RC suggest that Euo.9Ro.ITiO3 （R = La, Ce） compounds could be promising materials in low temperature and low magnetic field refrigerants.展开更多
SBA-15（mesoporous SiO2） is used to stabilize and transfer F-in the NH4BF4 CVD reaction for the first time, and a large-scale crystalline h-BN phase can be prepared. We successfully fabricate hollow h-BN capsules wit...SBA-15（mesoporous SiO2） is used to stabilize and transfer F-in the NH4BF4 CVD reaction for the first time, and a large-scale crystalline h-BN phase can be prepared. We successfully fabricate hollow h-BN capsules with collapsed surfaces in our designed NH4BF4 CVD system. Optimum temperature conditions are obtained, and a detailed formation mechanism is further proposed. The successful SBA-15-assisted NH4BF4 CVD route is of importance and enriches the engineering technology in the h-BN single-source CVD reaction.展开更多
Some color centers in diamond can serve as quantum bits which can be manipulated with microwave pulses and read out with laser,even at room temperature.However,the photon collection efficiency of bulk diamond is great...Some color centers in diamond can serve as quantum bits which can be manipulated with microwave pulses and read out with laser,even at room temperature.However,the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface.To address this issue,we fabricated arrays of diamond nanostructures,differing in both diameter and top end shape,with HSQ and Cr as the etching mask materials,aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy（NV） embedded diamond.With a mixture of O2 and CHF3 gas plasma,diamond pillars with diameters down to 45 nm were obtained.The top end shape evolution has been represented with a simple model.The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement,larger than tenfold,and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected.These results provide useful information for future applications of nanostructured diamond as a single-photon source.展开更多
We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 ...We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level （EF） originate from the hybridized Al p-C p and A1 p-N p states. The calculated bulk and Young＇s moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti3SiC2. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti2AlC and Ti2AlN, indicating that Al5C3N is a ductile ceramic.展开更多
The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode appl...The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. Four compound hosts of LaSiO2N, La4Si2OTN2, La5Si3012N, and La2Si603N8 were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce^3＋ substitution indicated that the covalency degree decreased in a sequence LaSiO2N 〉 La2Si603Ns 〉 La4Si2OTN2 〉 LasSi3O12N, not simply in correlation to the ratio of N3/O2. Excitation and emission spectrum measurements showed the main features of Ce^3＋ luminescence in the series： the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding; nephelauxetic effect could not be observed clearly for the investigated series; to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.展开更多
The magnetism and magnetocaloric effect in Er1-xGdxCoAl（x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1） were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel te...The magnetism and magnetocaloric effect in Er1-xGdxCoAl（x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1） were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature（T N）linearly increases from 14 K to 102 K, while the magnetic entropy change（-？S M） tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-？S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width（δT） in the-？S M–T curve and improve the refrigeration capacity.展开更多
We report on curled polyvinylpyrrolidone(PVP)microfibers fabricated by a modified electrospinning with a small nail as the tip collector.PVP(45 wt%)ethanol solution is electrospun under different working voltages rang...We report on curled polyvinylpyrrolidone(PVP)microfibers fabricated by a modified electrospinning with a small nail as the tip collector.PVP(45 wt%)ethanol solution is electrospun under different working voltages ranging from 10 to 15,20,30 and 40kV.It is found that with the increase of working voltage,the proportion of the curled fibers increases and the uniformity of the curled fibers improves,as well as the repeat distance of the curled structures reducing.Particularly,some curled fibers develop into helical structures under relatively high voltages.Further analyses indicate that the formation mechanism for the curled polymer fibers can be ascribed to electrical driven bending instability and/or mechanical jet buckling when hitting the collector surface.This modified electrospinning technique may be a cost-effective approach for the mass production of curled microfibers.展开更多
ZnO/TiO_(2) nanocomposite films on quartz substrates were prepared by the sol-gel method, and the corresponding optical absorption properties were investigated. In the ultraviolet region, it was found that the positio...ZnO/TiO_(2) nanocomposite films on quartz substrates were prepared by the sol-gel method, and the corresponding optical absorption properties were investigated. In the ultraviolet region, it was found that the position of fundamental absorption edge partially depends on the composition of the ZnO/TiO_(2 ) films, and shifts toward a shorter wavelength with the increasing content of ZnO in the films. Moreover, a blueshift of the absorption edge resulted from a quantum size effect and the quantum confinement effect was observed in the ZnO/TiO_(2) system.展开更多
The magnetic properties and magnetocaloric effect（MCE） in EuTi1-xCoxO3（x = 0, 0.025, 0.05, 0.075, 0.1） compounds have been investigated. When the Ti^4＋ ions were substituted by Co2＋ions, the delicate balance was...The magnetic properties and magnetocaloric effect（MCE） in EuTi1-xCoxO3（x = 0, 0.025, 0.05, 0.075, 0.1） compounds have been investigated. When the Ti^4＋ ions were substituted by Co2＋ions, the delicate balance was changed between antiferromagnetic（AFM） and ferromagnetic（FM） phases in the EuTiO3 compound. In EuTi1-xCoxO3 system, a giant reversible MCE and large refrigerant capacity（RC） were observed without hysteresis. The values of -△SM^max were evaluated to be around 10 J·kg^-1·K^-1 for EuTi0.95Co0.05O3 under a magnetic field change of 10 kOe. The giant reversible MCE and large RC suggests that EuTi1-xCoxO3 series could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.10974041)the Research Fund for the Dectoral Program of Higher Education,China(Grant No.20091317110005)+1 种基金the Key Projects of Chinese Ministry of Education(Grant No.209011)the Natural Science Foundation of Hebei
文摘Highly pure magnesium borate （Mg2B2O5） nanowires with an average diameter of - 30 nm, an average length of 15 μm, and a high aspect ratio of - 500 have been synthesized on a large scale via a two-step method. MgBO2（OH） nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B205 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 ℃. The important effect of the MgBO2（OH）-Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional （1D） nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire- reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0702704)the National Natural Science Foundation of China(Grant Nos.11504266,51676198,and 51371075)+1 种基金the Tianjin Natural Science Foundation,China(Grant No.17JCQNJC02300)the National Key Foundation for Exploring Scientific Instrument of China(Grant No.2014YQ120351)
文摘Giant reversible magnetocaloric effects and magnetic properties in Euo.9Ro.lTiO3 （R = La, Ce） are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitution of La （x = 0.1） and Ce （x = 0.1） ions for Eu2＋ ions. The values of -ASM and RC are evaluated to be 10.8 J/（kg.K） and 51.8 J/kg for Euo.gCeo.lTiO3 and 11 J/（kg.K） and 39.3 J/kg for Euo.9Lao.lTiO3 at a magnetic field change of I0 kOe, respectively. The large low-field enhancements of --ASM and RC can be attributed to magnetic phase transition. The giant reversible MCE and large RC suggest that Euo.9Ro.ITiO3 （R = La, Ce） compounds could be promising materials in low temperature and low magnetic field refrigerants.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51332005,51372066,51172060,51202055,and 21103056)
文摘SBA-15（mesoporous SiO2） is used to stabilize and transfer F-in the NH4BF4 CVD reaction for the first time, and a large-scale crystalline h-BN phase can be prepared. We successfully fabricate hollow h-BN capsules with collapsed surfaces in our designed NH4BF4 CVD system. Optimum temperature conditions are obtained, and a detailed formation mechanism is further proposed. The successful SBA-15-assisted NH4BF4 CVD route is of importance and enriches the engineering technology in the h-BN single-source CVD reaction.
基金Project supported by the National Key Research and Development Plan of China(Grant No.2016YFA0200402)the National Natural Science Foundation of China(Grants Nos.11574369,11574368,91323304,11174362,and 51272278)the FP7 Marie Curie Action(project No.295208)sponsored by the European Commission
文摘Some color centers in diamond can serve as quantum bits which can be manipulated with microwave pulses and read out with laser,even at room temperature.However,the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface.To address this issue,we fabricated arrays of diamond nanostructures,differing in both diameter and top end shape,with HSQ and Cr as the etching mask materials,aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy（NV） embedded diamond.With a mixture of O2 and CHF3 gas plasma,diamond pillars with diameters down to 45 nm were obtained.The top end shape evolution has been represented with a simple model.The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement,larger than tenfold,and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected.These results provide useful information for future applications of nanostructured diamond as a single-photon source.
基金supported by the National Natural Science Foundation of China (Grant No. 10974041)the Key Project of Science and Technology for Colleges in Hebei Province,China (Grant No. ZD2010120)
文摘We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level （EF） originate from the hybridized Al p-C p and A1 p-N p states. The calculated bulk and Young＇s moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti3SiC2. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti2AlC and Ti2AlN, indicating that Al5C3N is a ductile ceramic.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10974041)the Natural Science Foundation of Hebei Province of China (Grant No. E2010000084)
文摘The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. Four compound hosts of LaSiO2N, La4Si2OTN2, La5Si3012N, and La2Si603N8 were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce^3＋ substitution indicated that the covalency degree decreased in a sequence LaSiO2N 〉 La2Si603Ns 〉 La4Si2OTN2 〉 LasSi3O12N, not simply in correlation to the ratio of N3/O2. Excitation and emission spectrum measurements showed the main features of Ce^3＋ luminescence in the series： the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding; nephelauxetic effect could not be observed clearly for the investigated series; to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51322605 and 51271192)
文摘The magnetism and magnetocaloric effect in Er1-xGdxCoAl（x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1） were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature（T N）linearly increases from 14 K to 102 K, while the magnetic entropy change（-？S M） tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-？S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width（δT） in the-？S M–T curve and improve the refrigeration capacity.
基金Supported by the Program for New Century Excellent Talents in University of China under Grand No NCET-07-0472the National Natural Science Foundation of China under Grant No 11074138.
文摘We report on curled polyvinylpyrrolidone(PVP)microfibers fabricated by a modified electrospinning with a small nail as the tip collector.PVP(45 wt%)ethanol solution is electrospun under different working voltages ranging from 10 to 15,20,30 and 40kV.It is found that with the increase of working voltage,the proportion of the curled fibers increases and the uniformity of the curled fibers improves,as well as the repeat distance of the curled structures reducing.Particularly,some curled fibers develop into helical structures under relatively high voltages.Further analyses indicate that the formation mechanism for the curled polymer fibers can be ascribed to electrical driven bending instability and/or mechanical jet buckling when hitting the collector surface.This modified electrospinning technique may be a cost-effective approach for the mass production of curled microfibers.
基金Supported by the National Natural Science Foundation of China under Grant No.19834080the State Key Project of Fundamental Research of China.
文摘ZnO/TiO_(2) nanocomposite films on quartz substrates were prepared by the sol-gel method, and the corresponding optical absorption properties were investigated. In the ultraviolet region, it was found that the position of fundamental absorption edge partially depends on the composition of the ZnO/TiO_(2 ) films, and shifts toward a shorter wavelength with the increasing content of ZnO in the films. Moreover, a blueshift of the absorption edge resulted from a quantum size effect and the quantum confinement effect was observed in the ZnO/TiO_(2) system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11504266,51271192,51322605,and 51371075)the Natural Science Foundation of Tianjin,China(Grant No.17JCQNJC02300)
文摘The magnetic properties and magnetocaloric effect（MCE） in EuTi1-xCoxO3（x = 0, 0.025, 0.05, 0.075, 0.1） compounds have been investigated. When the Ti^4＋ ions were substituted by Co2＋ions, the delicate balance was changed between antiferromagnetic（AFM） and ferromagnetic（FM） phases in the EuTiO3 compound. In EuTi1-xCoxO3 system, a giant reversible MCE and large refrigerant capacity（RC） were observed without hysteresis. The values of -△SM^max were evaluated to be around 10 J·kg^-1·K^-1 for EuTi0.95Co0.05O3 under a magnetic field change of 10 kOe. The giant reversible MCE and large RC suggests that EuTi1-xCoxO3 series could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.
