CeOx films are deposited onto the surface of a SiO2 matrix embedded with Si nanocrystals (nc-Si/SiO2) by electron-beam evaporation of CeO2 powder in high vacuum. By tuning the thickness of the CeOx film, photolumine...CeOx films are deposited onto the surface of a SiO2 matrix embedded with Si nanocrystals (nc-Si/SiO2) by electron-beam evaporation of CeO2 powder in high vacuum. By tuning the thickness of the CeOx film, photoluminescence (PL) spectra centred at 330, 358, 378, 388, 400, and 450hm, respectively, are observed. It has been identified that the PL centred at 358, 388 and 400 nm are from cerium silicide compounds, and those centred at 330hm, 378nm are due to Ce^3+ ions, while the 450hm PL is from the defects in the SiO2 matrix.展开更多
Electronic structure of SmCo7-xHfx compound is calculated by using the multi-scattering Xα method. It is shown that a few of electrons can transfer to the Sm 5d orbital due to orbital hybridization between Sm and Co ...Electronic structure of SmCo7-xHfx compound is calculated by using the multi-scattering Xα method. It is shown that a few of electrons can transfer to the Sm 5d orbital due to orbital hybridization between Sm and Co atoms. The 3d-5d coupling is stronger, which is the main reason to result in the long-range ferromagnetic order between Sm and Co atoms in SmCo7-xHfx. According to the Stoner criterion, the result of spin-unpolarized calculation for the Sm5Co32Hf2 duster could lead to a better understanding of why the ferromagnetic SmCo7-xHfx is a stable phase. For the Sm5Co32Hf2 duster the Fermi level is situated at the overall maximum of the density of states. Moreover the duster wavefunctions at EF are antibonding and hence highly localized in real space, which would lead to a large value for the duster Stoner integral. Thus a rationalization for the magnetic stability of SmCo7-xHfx has been obtained.展开更多
In this paper,the synthesis of a novel polyoxovanadiumborate[Li(H2O)3]3[V12B18O48(OH)12(OH)]·(H2O)5by hydrothermal method.FTIR,2DFTIR and UV-Vis absorption spectroscopy were employed to explore the relationships ...In this paper,the synthesis of a novel polyoxovanadiumborate[Li(H2O)3]3[V12B18O48(OH)12(OH)]·(H2O)5by hydrothermal method.FTIR,2DFTIR and UV-Vis absorption spectroscopy were employed to explore the relationships between structure and properties of 3-D compound 1.展开更多
Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ...Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ceramics.Using a scanning transmission electron microscope as a unique platform for atomic-scale structure engineering,we demonstrate that twin platelets could be produced in carbides by engineering antisite defects.The antisite defects at metal sites in various layered ternary carbides are collectively and controllably generated,and the metal elements are homogenized by electron irradiation,which transforms a twin-like lamellae into nanotwin platelets.Accompanying chemical homogenization,α-Ti_(3)AlC_(2) transforms to unconventionalβ-Ti_(3)AiC_(2).The chemical homogeneity and the width of the twin platelets can be tuned by dose and energy of bombarding electrons.Chemically homogenized nanotwins can boost hardness by~45%.Our results provide a new way to produce ultrathin(<5 nm)nanotwin platelets in scientifically and technologically important carbide materials and showcase feasibility of defect engineering by an angstrom-sized electron probe.展开更多
For the reported chemical structures,the disordered fragments of the structure acting as hosts and guests are common and unmanageable for crystallographers.How to analyze and treat such disordered assemblies is an imp...For the reported chemical structures,the disordered fragments of the structure acting as hosts and guests are common and unmanageable for crystallographers.How to analyze and treat such disordered assemblies is an important task for crystallographers.It is often difficult for some researchers to refine the disordered structures,even to mechanically justify the refined consequence in the absence of expertise.Herein,some examples of disorder refinements selected from the literature,including the disordered assemblies of nitrate,perchlorate,alkyl,aromatic assemblies,and guest solvent molecules,are summarized and discussed to provide practical advice for investigating the disorders for crystallographic researchers and beginners.The refinement approach for these disordered assemblies is also discussed in detail,which is helpful for crystallographers.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 10374016, and the Science and Technology Commission of Shanghai under Grant No 03D J1400.
文摘CeOx films are deposited onto the surface of a SiO2 matrix embedded with Si nanocrystals (nc-Si/SiO2) by electron-beam evaporation of CeO2 powder in high vacuum. By tuning the thickness of the CeOx film, photoluminescence (PL) spectra centred at 330, 358, 378, 388, 400, and 450hm, respectively, are observed. It has been identified that the PL centred at 358, 388 and 400 nm are from cerium silicide compounds, and those centred at 330hm, 378nm are due to Ce^3+ ions, while the 450hm PL is from the defects in the SiO2 matrix.
基金Supported by the National High-Technology Research and Development Programme of China under Grant No 2002AA324050, and the Natural Science Foundation of Shandong Province under Grant Nos Y2002D9 and Y2004A10.
文摘Electronic structure of SmCo7-xHfx compound is calculated by using the multi-scattering Xα method. It is shown that a few of electrons can transfer to the Sm 5d orbital due to orbital hybridization between Sm and Co atoms. The 3d-5d coupling is stronger, which is the main reason to result in the long-range ferromagnetic order between Sm and Co atoms in SmCo7-xHfx. According to the Stoner criterion, the result of spin-unpolarized calculation for the Sm5Co32Hf2 duster could lead to a better understanding of why the ferromagnetic SmCo7-xHfx is a stable phase. For the Sm5Co32Hf2 duster the Fermi level is situated at the overall maximum of the density of states. Moreover the duster wavefunctions at EF are antibonding and hence highly localized in real space, which would lead to a large value for the duster Stoner integral. Thus a rationalization for the magnetic stability of SmCo7-xHfx has been obtained.
基金the NNSFC(21473030,1371033)Fujian Provincial Natural Science Foundation(2013J01042)the Open Fund of State Key Laboratory of Structural Chemistry(20130015)
文摘In this paper,the synthesis of a novel polyoxovanadiumborate[Li(H2O)3]3[V12B18O48(OH)12(OH)]·(H2O)5by hydrothermal method.FTIR,2DFTIR and UV-Vis absorption spectroscopy were employed to explore the relationships between structure and properties of 3-D compound 1.
文摘Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ceramics.Using a scanning transmission electron microscope as a unique platform for atomic-scale structure engineering,we demonstrate that twin platelets could be produced in carbides by engineering antisite defects.The antisite defects at metal sites in various layered ternary carbides are collectively and controllably generated,and the metal elements are homogenized by electron irradiation,which transforms a twin-like lamellae into nanotwin platelets.Accompanying chemical homogenization,α-Ti_(3)AlC_(2) transforms to unconventionalβ-Ti_(3)AiC_(2).The chemical homogeneity and the width of the twin platelets can be tuned by dose and energy of bombarding electrons.Chemically homogenized nanotwins can boost hardness by~45%.Our results provide a new way to produce ultrathin(<5 nm)nanotwin platelets in scientifically and technologically important carbide materials and showcase feasibility of defect engineering by an angstrom-sized electron probe.
基金supported by the National Natural Science Foundation of China(Nos.21671003 and 21201005)the High Performance Computing Center of Henan Normal University and the 111 Project(No.D17007)。
文摘For the reported chemical structures,the disordered fragments of the structure acting as hosts and guests are common and unmanageable for crystallographers.How to analyze and treat such disordered assemblies is an important task for crystallographers.It is often difficult for some researchers to refine the disordered structures,even to mechanically justify the refined consequence in the absence of expertise.Herein,some examples of disorder refinements selected from the literature,including the disordered assemblies of nitrate,perchlorate,alkyl,aromatic assemblies,and guest solvent molecules,are summarized and discussed to provide practical advice for investigating the disorders for crystallographic researchers and beginners.The refinement approach for these disordered assemblies is also discussed in detail,which is helpful for crystallographers.