Neutron powder diffraction and high-pressure synchrotron x-ray diffraction study of tantalum nitrides

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.

Neutron diffraction study on composite compound Nd_2 Co_7

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.

基于空间分辨中子衍射方法的锂离子电池电化学反应均匀性研究

锂离子电池作为一种具有复杂组成的电化学器件,其电化学反应的均匀性受多种因素影响,包括正负极材料成分、电池结构和制备工艺等。电池的局部电化学反应不均匀性将导致局部失效加剧,进而影响其电化学性能、循环稳定性和安全性。鉴于电池拆解分析不但会破坏其电芯结构,改变电极材料的化学性质,进而影响分析结果的准确性,本工作介绍并应用无损的空间分辨飞行时间中子衍射方法,对大尺寸软包锂离子电池电化学反应分布的均匀性展开研究。通过采集和分析毫米尺度测试区域的中子衍射数据,获得了全电池在初始状态和失效状态下锂离子嵌入石墨负极过程中的相变信息,并构建了全电池不同位置处的石墨负极多相含量分布和归一化后负极中的锂浓度分布图。此外,结合高精度三维X射线断层扫描方法,从电池厚度、电流密度和电解质浓度等多个角度,分析和探讨了这些因素对锂离子电池电化学反应均匀性的影响。空间分辨中子粉末衍射方法可以对不同类型和不同形状的金属离子电池中的电化学反应均匀性进行快速直接的检测,为电池结构性能优化和技术改进提供强有力的技术支持。

Formation of the structure-Ⅱgas hydrate from low-concentration propane mixed with methane

It has been recognized that a small amount of propane mixed with methane can change greatly in not only the thermodynamics but also the structural properties of gas hydrate.However,its mechanism is still not well understood yet.In this research,structure-Ⅱ(sⅡ)hydrate is synthesized using a methanepropane gas mixture with an initial mole ratio of 99:1,and it is found that large(5~(12)6~4)cages are cooccupied by multiple gases based on the rigid structure analysis of neutron diffraction data.The first principles calculation and molecular dynamics simulation are conducted to uncover the molecular mechanism for sⅡmethane-propane hydrate formation,revealing that the presence of propane inhibits the formation of structure-Ⅰ(sⅠ)hydrate but promotes sⅡhydrate formation.The results help to understand the accumulation mechanism of natural gas hydrate and benefit to optimize the condition for gas storage and transportation in hydrate form.

A High-Performance Solid-State Na–CO_(2)Battery with Poly(Vinylidene Fluoride-co-Hexafluoropropylene)−Na_(3.2)Zr_(1.9)Mg_(0.1)Si_(2)PO_(12)Electrolyte

The recovery and utilization of carbon dioxide(CO_(2))is the key to achieve the targets of peak carbon dioxide emissions and carbon neutrality.The Na-CO_(2)battery made with cheap alkali metal sodium and greenhouse gas CO_(2)is an effective strategy to consume CO_(2)and store clean renewable energy.However,the liquid electrolyte volatilization in the open battery system and inevitable dendrite growth restrict the application of Na-CO_(2)batteries.In this work,magnesium-doped Na_(3)Zr_(2)Si_(2)PO_(12)(NZSP)was studied as a solid electrolyte for solid-state Na-CO_(2)batteries.The ionic conductivity of Na_(3.2)Zr_(1.9)Mg_(0.1)Si_(2)PO_(12)reaches 1.16 mS cm^(−1)at room temperature by replacing Zr ions in Na_(3.2)Zr_(1.9)Mg_(0.1)Si_(2)PO_(12)with Mg ions,and the structural changes are analyzed by neutron powder diffraction.The composite electrolyte consisting of highly conductive Na_(3.2)Zr_(1.9)Mg_(0.1)Si_(2)PO_(12)and high processability poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)is utilized for the first time to assemble a solid-state Na-CO_(2)battery.The cell shows a full discharge capacity of 7720 mAh g^(−1)at 200 mA g^(−1).The middle gap voltage is lower than 2 V after 120 cycles at 200 mA g^(−1)and at a cut-off capacity of 500 mAh g^(−1).This work demonstrates a promising strategy to design high-performance solid-state Na-CO_(2)batteries.

LaNi_5D_x(x=0,0·3)化合物的中子粉末衍射研究

利用中子粉末衍射实验研究了LaNi5、LaNi5D0.3的晶体结构。在对LaNi5D0.3的中子粉末衍射数据进行分析时,考虑了吸、放气过程中引入的微应变会使得衍射轮廓产生各向异性展宽的因素,从而使拟合效果取得较明显的改善。与LaNi5一样,LaNi5D0.3的空间群仍为P6/mmm。LaNi5D0.3中氘原子占据12n位。

中国先进研究堆高分辨中子粉末衍射谱仪模拟研究

应用蒙特卡罗方法对中国先进研究堆 (CARR)上的高分辨中子粉末衍射谱仪 (HRPD)的物理设计进行了模拟研究。给出了谱仪的分辨率曲线、样品处中子通量密度等主要参数的模拟计算结果 ,讨论了高分辨模式和高强度模式下的分辨率和强度变化 。

CARR堆HRPD谱仪垂直聚焦单色器的选取和强度增益计算

垂直聚焦单色器技术是提高样品位置中子强度的有效手段。本文应用蒙特卡罗模拟方法对中国先进研究堆 (CARR)旁高分辨中子粉末衍射仪 (HRPD)的垂直聚焦单色器进行了优化选取 ,得到了垂直聚焦单色器高度、聚焦曲率半径和倾角等参数值 ,计算了使用垂直聚焦单色器相对于平板单色器的强度增益和样品处聚焦束尺寸。

用Rietica处理中子粉末衍射实验数据的方法

介绍了基于Rietveld轮廓精修方法的粉末衍射轮廓精修程序Rietica处理中子粉末衍射数据的方法,并以钙钛矿锰氧化物La0.69Ca0.31Mn0.96Fe0.04O3的拟合过程为例,具体说明了输入参数文件和数据文件的编写方法和程序运行方法。

La_(1-x)Ca_xMn_(0.96)Fe_(0.04)O_3(x=0.31、0.5、0.6)的中子衍射研究

利用Rietveld分析方法对钙钛矿锰氧化物La1-xCaxMn0.96Fe0.04O3(x=0.31、0.5、0.6)室温下中子衍射实验数据进行拟合。结果表明,La1-xCaxMn0.96Fe0.04O3化合物具有MnO6八面体,空间群为Pnma,La(Ca)原子占据4c晶位,Mn(Fe)原子占据4b晶位,O原子分别占据4c和8d晶位。根据拟合结果,计算出Mn O键的键长和Mn O Mn的键角,并对该系列样品结构和磁性能间的关系进行了简单讨论。

中子粉末衍射谱仪束流的椭圆聚焦镜设计

为使中子粉末衍射谱仪满足小样品研究需要,设计了一维椭圆聚焦镜系统并对参数进行了优化,同时对椭圆聚焦镜的相关参数做了较为详细讨论。采用椭圆解析计算和中子追迹程序McStas模拟两种方法,计算了椭圆聚焦镜参数对样品处中子注量率的影响,并以样品处中子注量率最大化为目标给出了优化参数,结果表明,在单色器(椭圆左焦点)到样品(椭圆右焦点)距离为2.7m情况下,采用超镜因子为3、长度为25cm的椭圆聚焦镜,其最佳位置为距离样品560mm处、椭圆长半轴为1 350.016mm,从而可以提高样品处注量率7倍。

PrFe_(10.5)V_(1.5)氮化物晶体和磁结构的中子衍射研究

用中子粉末衍射测量了 1∶12型稀土 铁金属间化合物Pr(Fe ,V) 12 及其氮化物Pr(Fe ,V) 12 Nx的晶体和磁结构。通过对衍射曲线的Rietveld峰形拟合 ,得出V择优占据ThMn12 型四角结构的 8i晶位和N原子进入 2b间隙晶位等结果 ,并讨论了氮化对磁性能的影响。

Nd_(0.5)Sr_(0.4)Pb_(0.1)Mn_(0.96)Fe_(0.04)O_3微观结构的中子衍射

采用固相反应法制备了混价钙钛矿型锰氧化物多晶样品Nd0.5Sr0.4Pb0.1Mn0.96Fe0.04O3,在室温下进行了中子粉末衍射测量并用Rietveld峰形精修程序Fullprof2k对实验数据进行了拟合。结果表明:Nd0.5Sr0.4Pb0.1Mn0.96Fe0.04O3样品具有正交的GdFeO3型结构,空间群为Pnma,Nd(Sr、Pb)原子占据4c晶位,Mn(Fe)原子占据4b晶位,O原子分别占据4c和8d两个不等价的晶位,并得到了MnO6八面体中Mn—O—Mn键角和Mn—O键的键长。

Impact of In^(3+) cations on structure and electromagnetic state of M-type hexaferrites

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.

Phase separation in Sr doped BiMnO_3

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.

Effects of charging rates on LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)(NMC622)/graphite Li-ion cells

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.

Influence of annealing treatment on structural and magnetic properties of double perovskite Sr_2FeMoO_6

The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance(MR) elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance (TMR) can be realized by regulating the grain size at appropriate annealing temperature.

Syntheses，Structures and Properties of Some New Composition Perovskite Compounds：Sr0．6Bi0．4FeO2．7，Sr1－xBixFeO3－y and Ba1．5Pt0．5Mn2O6

New composition perovskite-type compounds with formula Sr0.6Bi0.4FeO2.7,Sr1-xBixFeO3-y(x=0.1 to 0. 9 in interveral of 0.1),and Ba1.5Pt0.5Mn2O6 have been synthsized and structurally characterized.The crystal structure of Sr0.6Bi0.4FeO2.7has been determined by X-ray single crystal diffraction,and the data of neutron powder diffraction collected at both room temperature and elevated temperature(380℃).The compound Sr0.6Bi0.4FeO2.7 crystallizes in the cubic space group of Pm3m with Z=1,a=3.9330(6) at room temperature,a=3.9498(6)A at 380℃.The magnetic structure from the neutron powder diffraction data collected at room temperature is consistent with a simple G-type antiferromagnetism and has a magnetic moment of 4.98 μB per Fe atom.The structures of Sr1-xBixFeO3-y with x other than 0.4 were also refined from the X-ray powder diffraction data.The data were consistent with a tetragonal cell when x=0.1,a rhombohedral cell when x= 0.9,and a cubic cell for x=0.2～0.8.From single crystal X-ray diffraction data,Ba1.5Pt0.5Mn2O6 crystallizes in hexagonal space group of P63mc with a= 5.7722 (6),c=4.4504(9),V=128.42(2),Z=1.The Sr(1-x)BixFeO(3-y)are found to be a good electronic and ionic conductor.

Porous FeAl alloys via powder sintering:Phase transformation,microstructure and aqueous corrosion behavior

This study investigates the phase transformation and microstructure of porous Fe Al parts sintered from elemental powder mixtures using in-situ neutron diffraction and in-situ thermal dilatometry.A single B2 structured Fe Al phase was determined in the sintered Fe Al alloy.The combined effects of the Kirkendall porosity,transient liquid phase,and phase transformations associated with powder sintering all contribute to the swelling phenomenon of the final sintered part.The aqueous corrosion test indicates that the corrosion products include iron oxides in the porous Fe Al parts.The accumulation of corrosion products blocks the pore channel and decreases pore size and permeability over the soaking time.

Solvent-free mechanochemical synthesis of organic proton conducting salts incorporating imidazole and dicarboxylic acids

Solventless mechanochemical synthesis by manual grinding was applied to grow organic proton conducting salts,imidazole-succinic acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(2)COOH)and imidazole-glutaric acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(3)COOH).This synthesis method induces crystallization and provides the phase-pure compounds.The compounds exhibit different electric conducting behavior and activation energies Ea compared with the reported single crystals obtained from the solution method.The difference in conducting property can be related to intrinsic defects and structural disorder introduced by mechanochemical grinding,indicating that the mechanochemical method bears strong capability for tuning conductivities.Moreover,complete deuteration of the organic salts is achieved by the method.The mechanochemical synthesis of organic salts also holds high potential for the actual industrialized large-scale production.