MgxNi1-xFe_(2)O_(4)(x=0,0.25,0.5,0.75,1)spinel ferrite material was analyzed to determine its magnetic properties and structure.X-ray diffraction(XRD),Mössbauer spectroscopy,and vibrating sample magnetometer(VSM)...MgxNi1-xFe_(2)O_(4)(x=0,0.25,0.5,0.75,1)spinel ferrite material was analyzed to determine its magnetic properties and structure.X-ray diffraction(XRD),Mössbauer spectroscopy,and vibrating sample magnetometer(VSM)characterization were performed on the samples prepared using the sol-gel method.The results from XRD confirmed the existence of the single-phase cubic spinel structures Fd3m,as well as the evolution of the crystalline size(D),the lattice parameter(a)and cell volume in compounds.The Mössbauer spectra showed the distribution of cations and changes in the magnetic properties of the sample.VSM measurement revealed that the samples were room-temperature ferromagnetic.Moreover,the saturation magnetization(Ms)of the samples changed with the Mg^(2+)ion content x,and a maximum occured at x=0.5.Doping with Mg^(2+)ions increased the transfer of Ni^(2+)ions to tetrahedral sites,thus increasing the magnetic moment difference between tetrahedral(A)and octahedral(B)sites.Specifically,doping NiFe_(2)O_(4) with Mg^(2+)ions can enhance its magnetic properties and enhance its saturation magnetization.展开更多
Elucidation of a reaction mechanism is the most critical aspect for designing electrodes for highperformance secondary batteries.Herein,we investigate the sodium insertion/extraction into an iron fluoride hydrate(FeF_...Elucidation of a reaction mechanism is the most critical aspect for designing electrodes for highperformance secondary batteries.Herein,we investigate the sodium insertion/extraction into an iron fluoride hydrate(FeF_(3)·0.5H_(2)O)electrode for sodium-ion batteries(SIBs).The electrode material is prepared by employing an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate,which serves as a reaction medium and precursor for F^(-)ions.The crystal structure of FeF_(3)·0.5H_(2)O is observed as pyrochlore type with large open 3-D tunnels and a unit cell volume of 1129A^(3).The morphology of FeF_(3)·0.5H_(2)O is spherical shape with a mesoporous structure.The microstructure analysis reveals primary particle size of around 10 nm.The FeF_(3)·0.5H_(2)O cathode exhibits stable discharge capacities of 158,210,and 284 mA h g^(-1) in three different potential ranges of 1.5-4.5,1.2-4.5,and 1.0-4.5 V,respectively at 0.05 C rate.The specific capacities remained stable in over 50 cycles in all three potential ranges,while the rate capability was best in the potential range of 1.5-4.5 V.The electrochemical sodium storage mechanism is studied using X-ray absorption spectroscopy,indicating higher conversion at a more discharged state.Ex-situ M?ssbauer spectroscopy strengthens the results for reversible reduction/oxidation of Fe.These results will be favorable to establish high-performance cathode materials with selective voltage window for SIBs.展开更多
In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition met...In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.展开更多
In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition met...In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.展开更多
Ball milling for long time （such as 10, 20, and 30 h） can transform Fe84.94Si9,68A15.38 alloy powders with irregular shapes into flakes. X-ray diffraction （XRD） and M6ssbauer measurements have proven that the unmi...Ball milling for long time （such as 10, 20, and 30 h） can transform Fe84.94Si9,68A15.38 alloy powders with irregular shapes into flakes. X-ray diffraction （XRD） and M6ssbauer measurements have proven that the unmilled particles and the flakes obtained by milling for 10 h have the same D03-type superlattice structure. The flakes obtained by milling for 20 h and 30 h have the same disorder a-Fe（Si, A1） structure. There are more than 6 absorption peaks in the transmis- sion MSssbauer spectra （TMSs） for the particles with D03-type superlattice structure, which can be fitted with 5 sextets representing 5 different Fe-site environments. However, only 6 TMS absorption peaks have been found for particles with a disorder a-Fe（Si, A1） structure, which can be fitted with the distributions of M6ssbauer parameters （Bhf, isomer shift）. The TMS results show that the flaky particles have a stronger tendency to possess the planar magnetic anisotropy. As the result, the flakes have larger microwave permeability values than particles with irregular shapes. The conversion electron M6ssbauer spectra （CEMSs） also show the significantly different Fe-sites environments between the alloy surface and the inside.展开更多
Mixed-oxide nanostructures of the type xGd<sub>2</sub>O<sub>3</sub>-(1-x)α-Fe<sub>2</sub>O<sub>3</sub> (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical act...Mixed-oxide nanostructures of the type xGd<sub>2</sub>O<sub>3</sub>-(1-x)α-Fe<sub>2</sub>O<sub>3</sub> (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO<sub>3</sub> after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.11447231)the National Undergraduate Innovation and Entrepreneurship Training Program Support Projects of China+2 种基金the Natural Science Foundation of Hunan Province,China (Grant No.2020JJ4517)the Research Foundation of the Education Bureau of Hunan Province,China (Grant Nos.19A434,19A433,and 19C1621)the Opening Project of the Cooperative Innovation Center for Nuclear Fuel Cycle Technology and Equipment,University of South China (Grant Nos.2019KFY10 and 2019KFY09)。
文摘MgxNi1-xFe_(2)O_(4)(x=0,0.25,0.5,0.75,1)spinel ferrite material was analyzed to determine its magnetic properties and structure.X-ray diffraction(XRD),Mössbauer spectroscopy,and vibrating sample magnetometer(VSM)characterization were performed on the samples prepared using the sol-gel method.The results from XRD confirmed the existence of the single-phase cubic spinel structures Fd3m,as well as the evolution of the crystalline size(D),the lattice parameter(a)and cell volume in compounds.The Mössbauer spectra showed the distribution of cations and changes in the magnetic properties of the sample.VSM measurement revealed that the samples were room-temperature ferromagnetic.Moreover,the saturation magnetization(Ms)of the samples changed with the Mg^(2+)ion content x,and a maximum occured at x=0.5.Doping with Mg^(2+)ions increased the transfer of Ni^(2+)ions to tetrahedral sites,thus increasing the magnetic moment difference between tetrahedral(A)and octahedral(B)sites.Specifically,doping NiFe_(2)O_(4) with Mg^(2+)ions can enhance its magnetic properties and enhance its saturation magnetization.
基金supported by the Basic Science Research Program of the National Research Foundation(NRF)of South Koreafunded by the Ministry of Science&ICT and Future Planning(NRF-2020M3H4A3081889)KIST Institutional Program of South Korea(Project Nos.2E31860)。
文摘Elucidation of a reaction mechanism is the most critical aspect for designing electrodes for highperformance secondary batteries.Herein,we investigate the sodium insertion/extraction into an iron fluoride hydrate(FeF_(3)·0.5H_(2)O)electrode for sodium-ion batteries(SIBs).The electrode material is prepared by employing an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate,which serves as a reaction medium and precursor for F^(-)ions.The crystal structure of FeF_(3)·0.5H_(2)O is observed as pyrochlore type with large open 3-D tunnels and a unit cell volume of 1129A^(3).The morphology of FeF_(3)·0.5H_(2)O is spherical shape with a mesoporous structure.The microstructure analysis reveals primary particle size of around 10 nm.The FeF_(3)·0.5H_(2)O cathode exhibits stable discharge capacities of 158,210,and 284 mA h g^(-1) in three different potential ranges of 1.5-4.5,1.2-4.5,and 1.0-4.5 V,respectively at 0.05 C rate.The specific capacities remained stable in over 50 cycles in all three potential ranges,while the rate capability was best in the potential range of 1.5-4.5 V.The electrochemical sodium storage mechanism is studied using X-ray absorption spectroscopy,indicating higher conversion at a more discharged state.Ex-situ M?ssbauer spectroscopy strengthens the results for reversible reduction/oxidation of Fe.These results will be favorable to establish high-performance cathode materials with selective voltage window for SIBs.
文摘In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.
文摘In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.
基金supported by the National Key Basic Research Program of China(Grant No.2010CB334702)the China National Funds for Distinguished Young Scientists(Grant No.51025208)+1 种基金the International Collaboration Project of Sichuan Province,China(Grant Nos.2011HH0001 and 2012JQ0053)the Program for New Century Excellent Talents in Universities,China(Grant No.NCET-11-0060)
文摘Ball milling for long time （such as 10, 20, and 30 h） can transform Fe84.94Si9,68A15.38 alloy powders with irregular shapes into flakes. X-ray diffraction （XRD） and M6ssbauer measurements have proven that the unmilled particles and the flakes obtained by milling for 10 h have the same D03-type superlattice structure. The flakes obtained by milling for 20 h and 30 h have the same disorder a-Fe（Si, A1） structure. There are more than 6 absorption peaks in the transmis- sion MSssbauer spectra （TMSs） for the particles with D03-type superlattice structure, which can be fitted with 5 sextets representing 5 different Fe-site environments. However, only 6 TMS absorption peaks have been found for particles with a disorder a-Fe（Si, A1） structure, which can be fitted with the distributions of M6ssbauer parameters （Bhf, isomer shift）. The TMS results show that the flaky particles have a stronger tendency to possess the planar magnetic anisotropy. As the result, the flakes have larger microwave permeability values than particles with irregular shapes. The conversion electron M6ssbauer spectra （CEMSs） also show the significantly different Fe-sites environments between the alloy surface and the inside.
文摘Mixed-oxide nanostructures of the type xGd<sub>2</sub>O<sub>3</sub>-(1-x)α-Fe<sub>2</sub>O<sub>3</sub> (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO<sub>3</sub> after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.
