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.

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.

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.

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.

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.

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.

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.

Manipulating non-collinear antiferromagnetic order and thermal expansion behaviors in triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N

Magnetic materials with non-collinear spin orderings provide an outstanding platform to probe spin-tronic phenomena owing to their strong spin-orbit coupling(SOC)and unique Berry phase.It is thus important to obtain a non-collinear antiferromagnetic(AFM)phase at room temperature(RT).Signifi-cantly,the discovery of novel materials with nearly zero thermal expansion(ZTE)property near RT is required and pursued for avoiding thermal stress and fracture in spintronic devices.Herein,the doping of Sn(Ge)at the Ag site in the triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N compounds increases effectively the Neel point and makes the interesting non-collinearГ^(5g)AFM phase exist above RT.The magnetic phase diagrams withГ^(5g)phase up to 498 K were built by the combined analysis of neutron powder diffraction(NPD),magnetic measurements,electronic transport,and differential scanning calorimetry(DSC).The thermal expansion behaviors of Mn_(3)Ag_(1-x)Sn(Ge)_(x)N were modulated,and the nearly ZTE above RT was achieved in Mn_(3)Ag_(0.5)Ge_(0.5)N withinГ^(5g)AFM ordering.Our findings offer an effective way to tailor the non-collinear AFM ordering and correlated thermal expansion behavior for potential use in the emerging field of thermal stress-free magnetic chip materials.

Oxygen vacancy migration and its lattice structural origin in A-site non-stoichiometric bismuth sodium titanate perovskites

Off-stoichiometry of perovskite structural Bi0.5Na0.5TiO3(BNT)ferroelectrics can give rise to considerable oxide-ion conductivity.The inherent structural characteristics are urgent to be resolved due to its particular sensitivity of the conduction mechanism to the nominal composition and synthesis process.Herein,a thorough study of the temperature-dependent neutron,X-ray diffraction and Raman spectrum is carried out on a series of equivalently substituted A-site deficient non-stoichiometric and pristine BNT.Phase transition and defect association are systemically investigated in these dominated rhombohedral phases at room temperature,associated with well saturated ferroelectric states.Significant structural evolution identified by Rietveld refinements and the origin of the electrical performance are clarified at elevated temperatures,focusing on the subtle distortions of ionic displacements,oxygen octahedral tilts and local chemical environments for oxygen vacancies.The ion migration ability mediated by oxygen vacancies that are not energetically favorable in BNT mainly depends on the external substitutional disorder,and is strongly affected by the dopant concentration.Together with the lone pair substitution concept,superior oxide ionic conductivity is achieved,and an alternative strategy is provided in designing BNT based oxide ion conductors.

The critical role of spin rotation in the giant magnetostriction of La(Fe,Al)_(13)

As an efficient converter between electromagnetic and mechanical energies, magnetostriction is an intriguing property for not only fundamental studies but also technological applications. However, the understanding of its microscopic origin remains challenging, which is critical for the development of magnetostriction materials. Here, the critical role of spin rotation in the giant magnetostriction of La(Fe,Al)_(13) is first revealed by the in-situ magnetic and temperature field of neutron powder diffraction. The giant magnetostriction originates from magnetic-field-driven spin moment rotation of canting structure, in which the sharp increase of ferromagnetic component causes the elongation of icosahedron inside of lattice. Furthermore, it is the first time to reveal the accurate canting antiferromagnetic structure in La(Fe,Al)_(13). The present study provides a new strategy, i.e., the spin rotation, for exploring new magnetostriction functional materials.

Structural insights into lithium-deficient type Li-rich layered oxide for high-performance cathode

As one of the promising candidate cathode materials for the high-performance lithium-ion batteries,Li-rich layered oxides still suffer from a series of critical drawbacks,such as voltage decay,oxygen release,irrevers-ible migration of transition metal ions,etc.In this work,Li-deficient method has been confirmed as an effective approach to improve the overall electrochemical performances of Li-rich cathode.The optimized lithium-deficient Li-rich layered cathode exhibits splendid discharge capacity of~297 mAh/g at 0.1 C and prominent rate per-formance of-143 mAh/g at 5 C.Subsequently,neutron diffraction in combination with Raman spectroscopy is applied to explore and clarify the underlying mechanism for improved performances.It was found that the lithium-deficient induced nickel migration and oxygen vacancy play an significant role in improving electro-chemical performances,because migration of nickel into Li layer is able to expand the Li layer spacing and reduce the Li/Ni antisite,leading to facilitated diffusion of lithium ions.Moreover,the formation of oxygen vacancy is able to promote anionic redox processes and suppress the gas release,thus leading to higher capacity.The results present valuable structural insights into the influence of lithium deficiency and provide guidance for the devel-opment of Li-rich cathode materials.

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.