Neutron diffraction techniques of large-volume samples at high pressure using compact opposed-anvil cells are developed at a reactor neutron source, China＇s Mianyang research reactor. We achieve a high-pressure condi...Neutron diffraction techniques of large-volume samples at high pressure using compact opposed-anvil cells are developed at a reactor neutron source, China＇s Mianyang research reactor. We achieve a high-pressure condition of in situ neutron diffraction by means of a newly designed large-volume opposed-anvil cell. This pressure calibration is based on resistance measurements of bismuth and the neutron diffraction of iron. Pressure calibration experiments are performed at room temperature for a new cell using the tungsten carbide anvils with a tapered angle of 30°, Φ4.5 mm culet diameter and the metal-nonmetal composite gasket with a thickness of 2 mm. Transitions in Bi（Ⅰ–Ⅱ 2.55 GPa, Ⅱ–V 7.7 GPa） are observed at 100 and 300 kN, respectively, by resistance measurements.The pressure measurement results of neutron diffraction are consistent with resistance measurements of bismuth.As a result, pressures up to about 7.7 GPa can routinely and stably be achieved using this apparatus, with the sample volume of 9 mm^3.展开更多
The magnetic structure of the spin-chain antiferromagnet SrCo2 V208 is determined by single-crystal neutron diffraction experiment. The system undergoes a long-range magnetic order below the critical temperature TN=4....The magnetic structure of the spin-chain antiferromagnet SrCo2 V208 is determined by single-crystal neutron diffraction experiment. The system undergoes a long-range magnetic order below the critical temperature TN=4.96 K. The moment of 2.16#B per Co at 1.6K in the screw chain running along the c axis Mternates in the c axis. The moments of neighboring screw chains are arranged antiferromagnetically along one in-plane axis and ferromagnetieally Monk the other in-plane axis. This magnetic configuration breaks the four-fold symmetry of the tetragonM crystal structure and leads to two equally populated magnetic twins with the antiferromagnetic vector in the a or b axis. The very similar magnetic state to the isostructural BaCo2 V~ 08 warrants SrCo2 V2 08 as another interesting half-integer spin-chain antiferromagnet for investigation on quantum antiferromagnetism.展开更多
The magnetic structure of CsCo_2 Se_2 was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector（0,0,1） was observed at TN= 78 K. The Co magnetic...The magnetic structure of CsCo_2 Se_2 was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector（0,0,1） was observed at TN= 78 K. The Co magnetic moment 0.772（6） μB at 10 K pointing in the basal plane couples ferromagnetically in the plane, which stacks antiferromagnetically along the c direction. Tuning and suppressing the interplane antiferromagnetic interaction may be crucial to induce a superconducting state in the material.展开更多
The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement sho...The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La（Fe11.4Al1.6）C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites： FeI （8b） and FeII （96i）, and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La（Fe11.4Al1.6）C0.02 has no net magnetization in the paramagnetic （T 〉 TN = 182 K） or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.展开更多
The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound...The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2NiT-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCus-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3＋ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3＋ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound.展开更多
Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated...Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure- volume （P-V） sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B0 = 369（2） GPa with pressure derivatives of B~ = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result （Bo = 351 GPa）, which is close to the recent theoretical calculation result （Bo = 378 GPa）. An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.展开更多
The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Underst...The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Understanding the mechanism of the structure transition and atom rearrangement via synthesis or processing is key to expediting the exploration of excellent energy materials. In this work, in situ neutron scattering is employed to reveal the real-time structure evolution, including the TM-O bonds, lattice,TM valence and the migration of the high-voltage spinel cathode LiNi_(0.5)Mn_(1.5)O_(4). The transition-metalmediated spinel destabilization under the annealing at the oxygen-deficient atmosphere is pinpointed.The formation of Mn^(3+) is correlated to the TM migration activation, TM disordered rearrangement in the spinel, and the transition to a layered-rocksalt phase. The further TM interdiffusion and Mn^(3+) reduction are also revealed with multi-stage thermodynamics and kinetics. The mechanisms of phase transition and atom migrations as functions of temperature, time and atmosphere present important guidance on the synthesis in various-valence element containing oxides.展开更多
In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12...In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12）Co_7 series, R_3 Co series and RCu_2series）, which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin（S） and atoms with large total angular momentum（J） are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change（？SM）, refrigerant temperature width（Twidth）or refrigerant capacity（RC） is enlarged for some R–T compounds. In the low temperature range, binary R–T（R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series,R_（12）Co_7 series, R_3 Co series and RCu_2series） show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.展开更多
A simple and convenient pressure calibration method is developed for a newly designed portable wide-access ＇panoramic＇ cell. This cell is adapted to angle-dispersive-mode high-pressure in situ neutron diffraction of...A simple and convenient pressure calibration method is developed for a newly designed portable wide-access ＇panoramic＇ cell. This cell is adapted to angle-dispersive-mode high-pressure in situ neutron diffraction of reactor neutron sources. This pressure calibration method has established a relationship between the cell pressure and the anvil displace- ment （gasket compression） based on the fixed-point calibration technique. By employing TiZr gasket with a thickness of 3 mm and WC anvil with a culet of 4 mm diameter, the average anvil displacements are 1.31 mm and 2.22 mm for Bi phase transitions （2.55 GPa and 7.7 GPa）, and 1.85 mm for Ba phase transitions （5.5 GPa）, respectively. In this pressure range, the pressure increases quickly with decreasing gasket thickness, and undergoes a linear increase with the anvil displacement. By extrapolating the calibration curve, the cell pressure will achieve 10 GPa when the anvil displacement is around 2.5 ram.展开更多
Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties,especially their interesting hard magnetic properties.In this paper,we have summarized the mag...Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties,especially their interesting hard magnetic properties.In this paper,we have summarized the magnetic and structural properties of Mn-based intermetallic compounds(Mn X,where X=Al,Bi,and Ga).Various methods for synthesizing single phases of MnAl,MnBi,and Mnx Ga were developed in our lab.A very high saturation magnetization of 125 emu/g,coercivity of 5 kOe,and maximum energy product(BH)_(max)of 3.1 MG·Oe were achieved at room temperature for the pureτ-Mn–Al magnetic phase without carbon doping and the extrusion process.Low temperature phase(LTP)MnBi with a purity above 95 wt.%can be synthesized.An abnormal temperature coefficient of the coercivity was observed for the LTP MnBi magnet.Its coercivity increased with temperature from 100 K to 540 K,reached a maximum of 2.5 T at about540 K,and then decreased slowly to 1.8 T at 610 K.The positive temperature coefficient of the coercivity is related to the evolution of the structure and magnetocrystalline anisotropy field of the LTP MnBi phase with temperature.The LTP MnBi bonded magnets show maximum energy products(BH)_(max)of 8.9 MG·Oe(70 kJ/m^(3))and 5.0 MG·Oe(40 k J/m^(3))at room temperature and 400 K,respectively.Ferrimagnetic Mn_(x)Ga phases with L10 structures(x〈2.0)and D0_(22)structures(x〉2.0)were obtained.All of the above structures can be described by a D0_(22)supercell model in which 2 a-Ga and 2 b-Mn are simultaneously substituted.The tetragonal D0_(22)phases of the Mn_(x)Ga show high coercivities ranging from 7.2 kOe for low Mn content x=1.8 to 18.2 kOe for high Mn content x=3 at room temperature.The Mn_(1.2)Ga sample exhibits a room temperature magnetization value of 80 emu/g.The hard magnetic properties of coercivityiH_(c)=3.5 kOe,remanence M_(r)=43.6 emu/g,and(BH)_(max)=2.5 MG·Oe were obtained at room temperature.Based on the above studies,we believe that Mn-based magnetic materials could be promising candidates for rare earth free permanent magnets exhibiting a high Curie temperature,high magnetocrystalline anisotropy,and very high coercivity.展开更多
In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe conten...In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn（3） sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn（3） sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12（CH3COO）16（H2O）4]·2CH3COOH·4H2O （x = 1, 2, 3, and 4）, denoted by Mn11Fe1, Mn10Fe2, MngFe3, and Mn8Fe4, respectively.展开更多
The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0...The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0.1-1.2） solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range （from 4.2 K to 150 K）. It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFet2_xAlxO19 （x = 0.1-1.2） solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.展开更多
The solid solutions of In^(3+) doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method,and Rietveld analysis of the neutron diffraction patterns was conducted.In^(3+) cations...The solid solutions of In^(3+) doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method,and Rietveld analysis of the neutron diffraction patterns was conducted.In^(3+) cations occupy octahedral (4f_(Ⅵ)and 12 k) and tetrahedral (4f_(Ⅳ)) positions (SG=P6_(3)/mmc(No.194)).The average particle size is 837–650 nm.Curie tempearature (T_(C)) of the compounds monotonically decreased down to~520 K with increasing x.A frustrated magnetic state was detected from ZFC and FC magnetizations.saturation magnetization (M_(s)) and effective magnetocrystalline anisotropy coefficient (k_(eff)) were determined using the law of approach to saturation.A real permittivity (ε″) maximum of~3.3 at~45.5 GHz and an imaginary permittivity (ε′) of~1.6 at~42.3 GHz were observed for x=0.1.A real permeability (μ′) maximum of~1.5 at~36.2 GHz was observed for x=0.Aμ″imaginary permeability maximum of~0.8 at~38.3 GHz was observed for x=0.1.The interpretation of the results is based on the type of dielectric polarization and the natural ferromagnetic resonance features.展开更多
Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles.Increasing the charging rates from state-of-the-art 2 C(30 min)to 6 C(10 min)requires deep un...Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles.Increasing the charging rates from state-of-the-art 2 C(30 min)to 6 C(10 min)requires deep understanding on the cell aging mechanism.In this study,400 mAh pouch cells are cycled at 1 C,4 C and 6 C charging rates with 1 C discharging rate.Capacity fading,cathode structural changes,Li inventory loss,electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization techniques.The rapid capacity fading in cells at 6 C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging rate.Post-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.展开更多
Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and...Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and physical property measurements. All the experiments indicate that a phase separation occurs at the temperature coinciding with the reported charge ordering temperature （Tco） in the literature. Below the reported TCO, both the phases resulting from the phase separation crystallize in the orthorhombically distorted perovskite structure with space group Imma. At lower temperature, these two phases order in the CE-type antiferromagnetic structure and the A-type antiferromagnetic structure, respectively. However, a scrutiny of the high-resolution NPD and XRD data at different temperatures and the electron diffraction exper- iment at 300 K did not manifest any evidence of a long-range charge ordering （CO） in our investigated samples, suggesting that the anomalies of physical properties such as magnetization, electric transport, and lattice parameters at the TCO might be caused by the phase separation rather than by a CO transition.展开更多
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFA0401503the Science Challenge Project under Grant No TZ2016001the National Natural Science Foundation of China under Grant No 11427810
文摘Neutron diffraction techniques of large-volume samples at high pressure using compact opposed-anvil cells are developed at a reactor neutron source, China＇s Mianyang research reactor. We achieve a high-pressure condition of in situ neutron diffraction by means of a newly designed large-volume opposed-anvil cell. This pressure calibration is based on resistance measurements of bismuth and the neutron diffraction of iron. Pressure calibration experiments are performed at room temperature for a new cell using the tungsten carbide anvils with a tapered angle of 30°, Φ4.5 mm culet diameter and the metal-nonmetal composite gasket with a thickness of 2 mm. Transitions in Bi（Ⅰ–Ⅱ 2.55 GPa, Ⅱ–V 7.7 GPa） are observed at 100 and 300 kN, respectively, by resistance measurements.The pressure measurement results of neutron diffraction are consistent with resistance measurements of bismuth.As a result, pressures up to about 7.7 GPa can routinely and stably be achieved using this apparatus, with the sample volume of 9 mm^3.
基金Supported by the National Basic Research Program of China under Grant Nos 2012CB921700 and 2011CBA00112the National Natural Science Foundation of China under Grant Nos 11034012 and 11190024
文摘The magnetic structure of the spin-chain antiferromagnet SrCo2 V208 is determined by single-crystal neutron diffraction experiment. The system undergoes a long-range magnetic order below the critical temperature TN=4.96 K. The moment of 2.16#B per Co at 1.6K in the screw chain running along the c axis Mternates in the c axis. The moments of neighboring screw chains are arranged antiferromagnetically along one in-plane axis and ferromagnetieally Monk the other in-plane axis. This magnetic configuration breaks the four-fold symmetry of the tetragonM crystal structure and leads to two equally populated magnetic twins with the antiferromagnetic vector in the a or b axis. The very similar magnetic state to the isostructural BaCo2 V~ 08 warrants SrCo2 V2 08 as another interesting half-integer spin-chain antiferromagnet for investigation on quantum antiferromagnetism.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB921700)the National Natural Science Foundation of China(Grant No.11190024)+2 种基金the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(Grant Nos.17XNLF04 and 17XNLF06)support from China Scholarship Council
文摘The magnetic structure of CsCo_2 Se_2 was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector（0,0,1） was observed at TN= 78 K. The Co magnetic moment 0.772（6） μB at 10 K pointing in the basal plane couples ferromagnetically in the plane, which stacks antiferromagnetically along the c direction. Tuning and suppressing the interplane antiferromagnetic interaction may be crucial to induce a superconducting state in the material.
基金supported by the National Basic Research Program of China (973 Program) (Grant No. 2010CB833102)the National Natural Science Foundation of China (Grant No. 10974244)
文摘The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La（Fe11.4Al1.6）C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites： FeI （8b） and FeII （96i）, and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La（Fe11.4Al1.6）C0.02 has no net magnetization in the paramagnetic （T 〉 TN = 182 K） or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.
基金supported by the National Natural Science Foundation of China (Grant No. 50631040)the National Basic Research Program of China (Grants Nos. 2006CB601101 and 2006CB605101)
文摘The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2NiT-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCus-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3＋ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3＋ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound.
基金Project supported by the Research Foundation of Key Laboratory of Neutron Physics(Grant No.2015BB03)the National Natural Science Foundation of China(Grant Nos.11774247)+2 种基金the Science Foundation for Excellent Youth Scholars of Sichuan University(Grant No.2015SCU04A04)the Joint Usage/Research Center PRIUS(Ehime University,Japan)Chinese Academy of Sciences(Grant No.2017-BEPC-PT-000568)
文摘Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure- volume （P-V） sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B0 = 369（2） GPa with pressure derivatives of B~ = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result （Bo = 351 GPa）, which is close to the recent theoretical calculation result （Bo = 378 GPa）. An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.
基金supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy (DOE)。
文摘The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Understanding the mechanism of the structure transition and atom rearrangement via synthesis or processing is key to expediting the exploration of excellent energy materials. In this work, in situ neutron scattering is employed to reveal the real-time structure evolution, including the TM-O bonds, lattice,TM valence and the migration of the high-voltage spinel cathode LiNi_(0.5)Mn_(1.5)O_(4). The transition-metalmediated spinel destabilization under the annealing at the oxygen-deficient atmosphere is pinpointed.The formation of Mn^(3+) is correlated to the TM migration activation, TM disordered rearrangement in the spinel, and the transition to a layered-rocksalt phase. The further TM interdiffusion and Mn^(3+) reduction are also revealed with multi-stage thermodynamics and kinetics. The mechanisms of phase transition and atom migrations as functions of temperature, time and atmosphere present important guidance on the synthesis in various-valence element containing oxides.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274357,51501005,51590880,and 11674008)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-15-010A1)+1 种基金the China Postdoctoral Science Foundation(Grant No.2016M591071)the Key Research Program of the Chinese Academy of Sciences(Grant No.KJZD-EW-M05)
文摘In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12）Co_7 series, R_3 Co series and RCu_2series）, which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin（S） and atoms with large total angular momentum（J） are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change（？SM）, refrigerant temperature width（Twidth）or refrigerant capacity（RC） is enlarged for some R–T compounds. In the low temperature range, binary R–T（R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series,R_（12）Co_7 series, R_3 Co series and RCu_2series） show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.
基金supported by the National Natural Science Foundation of China(Grant Nos.91126001,11105128,and 51231002)
文摘A simple and convenient pressure calibration method is developed for a newly designed portable wide-access ＇panoramic＇ cell. This cell is adapted to angle-dispersive-mode high-pressure in situ neutron diffraction of reactor neutron sources. This pressure calibration method has established a relationship between the cell pressure and the anvil displace- ment （gasket compression） based on the fixed-point calibration technique. By employing TiZr gasket with a thickness of 3 mm and WC anvil with a culet of 4 mm diameter, the average anvil displacements are 1.31 mm and 2.22 mm for Bi phase transitions （2.55 GPa and 7.7 GPa）, and 1.85 mm for Ba phase transitions （5.5 GPa）, respectively. In this pressure range, the pressure increases quickly with decreasing gasket thickness, and undergoes a linear increase with the anvil displacement. By extrapolating the calibration curve, the cell pressure will achieve 10 GPa when the anvil displacement is around 2.5 ram.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51731001,11805006,51371009,11504348,and 11675006)National Key Research and Development Program of China(Grant Nos.2016YFB0700901,2017YFA0401502,and 2017YFA0206303)
文摘Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties,especially their interesting hard magnetic properties.In this paper,we have summarized the magnetic and structural properties of Mn-based intermetallic compounds(Mn X,where X=Al,Bi,and Ga).Various methods for synthesizing single phases of MnAl,MnBi,and Mnx Ga were developed in our lab.A very high saturation magnetization of 125 emu/g,coercivity of 5 kOe,and maximum energy product(BH)_(max)of 3.1 MG·Oe were achieved at room temperature for the pureτ-Mn–Al magnetic phase without carbon doping and the extrusion process.Low temperature phase(LTP)MnBi with a purity above 95 wt.%can be synthesized.An abnormal temperature coefficient of the coercivity was observed for the LTP MnBi magnet.Its coercivity increased with temperature from 100 K to 540 K,reached a maximum of 2.5 T at about540 K,and then decreased slowly to 1.8 T at 610 K.The positive temperature coefficient of the coercivity is related to the evolution of the structure and magnetocrystalline anisotropy field of the LTP MnBi phase with temperature.The LTP MnBi bonded magnets show maximum energy products(BH)_(max)of 8.9 MG·Oe(70 kJ/m^(3))and 5.0 MG·Oe(40 k J/m^(3))at room temperature and 400 K,respectively.Ferrimagnetic Mn_(x)Ga phases with L10 structures(x〈2.0)and D0_(22)structures(x〉2.0)were obtained.All of the above structures can be described by a D0_(22)supercell model in which 2 a-Ga and 2 b-Mn are simultaneously substituted.The tetragonal D0_(22)phases of the Mn_(x)Ga show high coercivities ranging from 7.2 kOe for low Mn content x=1.8 to 18.2 kOe for high Mn content x=3 at room temperature.The Mn_(1.2)Ga sample exhibits a room temperature magnetization value of 80 emu/g.The hard magnetic properties of coercivityiH_(c)=3.5 kOe,remanence M_(r)=43.6 emu/g,and(BH)_(max)=2.5 MG·Oe were obtained at room temperature.Based on the above studies,we believe that Mn-based magnetic materials could be promising candidates for rare earth free permanent magnets exhibiting a high Curie temperature,high magnetocrystalline anisotropy,and very high coercivity.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10375088 and 10505029）. Acknowledgment The authors thank Dr Denis Sheptyakov at PSI for much support of the neutron diffraction experiments.
文摘In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn（3） sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn（3） sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12（CH3COO）16（H2O）4]·2CH3COOH·4H2O （x = 1, 2, 3, and 4）, denoted by Mn11Fe1, Mn10Fe2, MngFe3, and Mn8Fe4, respectively.
基金supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST“MISiS”(Grant No.K4-2015-040)
文摘The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0.1-1.2） solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range （from 4.2 K to 150 K）. It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFet2_xAlxO19 （x = 0.1-1.2） solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.
基金conducted with financial support from the Russian Science Foundation (Agreement No. 19-19-00694 of 06 May 2019)。
文摘The solid solutions of In^(3+) doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method,and Rietveld analysis of the neutron diffraction patterns was conducted.In^(3+) cations occupy octahedral (4f_(Ⅵ)and 12 k) and tetrahedral (4f_(Ⅳ)) positions (SG=P6_(3)/mmc(No.194)).The average particle size is 837–650 nm.Curie tempearature (T_(C)) of the compounds monotonically decreased down to~520 K with increasing x.A frustrated magnetic state was detected from ZFC and FC magnetizations.saturation magnetization (M_(s)) and effective magnetocrystalline anisotropy coefficient (k_(eff)) were determined using the law of approach to saturation.A real permittivity (ε″) maximum of~3.3 at~45.5 GHz and an imaginary permittivity (ε′) of~1.6 at~42.3 GHz were observed for x=0.1.A real permeability (μ′) maximum of~1.5 at~36.2 GHz was observed for x=0.Aμ″imaginary permeability maximum of~0.8 at~38.3 GHz was observed for x=0.1.The interpretation of the results is based on the type of dielectric polarization and the natural ferromagnetic resonance features.
基金sponsored by the Office of Energy Efficiency and Renewable Energy(EERE)Vehicle Technologies Office(VTO)(Technology Manager:Brian Cunningham)sponsored research in accordance with the DOE Public Access Plan(http://energy.gov/downloads/doe-public-access-plan)。
文摘Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles.Increasing the charging rates from state-of-the-art 2 C(30 min)to 6 C(10 min)requires deep understanding on the cell aging mechanism.In this study,400 mAh pouch cells are cycled at 1 C,4 C and 6 C charging rates with 1 C discharging rate.Capacity fading,cathode structural changes,Li inventory loss,electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization techniques.The rapid capacity fading in cells at 6 C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging rate.Post-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11074295 and 50872148)the Natural Science Foundation of Guangxi Province,China(Grant No.2012GXNSFGA060002)
文摘Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and physical property measurements. All the experiments indicate that a phase separation occurs at the temperature coinciding with the reported charge ordering temperature （Tco） in the literature. Below the reported TCO, both the phases resulting from the phase separation crystallize in the orthorhombically distorted perovskite structure with space group Imma. At lower temperature, these two phases order in the CE-type antiferromagnetic structure and the A-type antiferromagnetic structure, respectively. However, a scrutiny of the high-resolution NPD and XRD data at different temperatures and the electron diffraction exper- iment at 300 K did not manifest any evidence of a long-range charge ordering （CO） in our investigated samples, suggesting that the anomalies of physical properties such as magnetization, electric transport, and lattice parameters at the TCO might be caused by the phase separation rather than by a CO transition.
