Range Order Effects Research Articles

Switching between solid solution and two-phase regimes in the Li1-xFe1-yMnyPO4 cathode materials during lithium (de)insertion: combined PITT, in situ XRPD and electron diffraction tomography study

The electrochemical properties and phase transformations during (de)insertion of Li+ in LiFePO4, LiFe0.9Mn0.1PO4 and LiFe0.5Mn0.5PO4 are studied by means of galvanostatic cycling, potential intermittent titration technique (PITT) and in situ X-ray powder diffraction. Different modes of switching between the solid solution and two-phase regimes are revealed which are influenced by the Mn content in Li1-xFe1-yMnyPO4. Additionally, an increase in electrochemical capacity with the Mn content is observed at high rates of galvanostatic cycling (10C, 20C), which is in good agreement with the numerically estimated contribution of the solid solution mechanism determined from PITT data. The observed asymmetric behavior of the phase transformations in Li1-xFe0.5Mn0.5PO4 during charge and discharge is discussed. For the first time, the crystal structures of electrochemically deintercalated Li1-xFe0.5Mn0.5PO4 with different Li content – LiFe0.5Mn0.5PO4, Li0.5Fe0.5Mn0.5PO4 and Li0.1Fe0.5Mn0.5PO4 – are refined, including the occupancy factors of the Li position. This refinement is done using electron diffraction tomography data. The crystallographic analyses of Li1-xFe0.5Mn0.5PO4 reveal that at x=0.5 and 0.9 the structure retains the Pnma symmetry and the main motif of the pristine x=0 structure without noticeable short range order effects.

Synergistic enhancing effect of N+C alloying on cyclic deformation behaviors in austenitic steel

Cyclic plastic and elastic strain controlled deformation behaviors of Mn18Cr7 austenitic steel with N0.6C0.3 synergistic enhancing alloying have been investigated using tension-compression low cycle fatigue and three-point bending high cycle fatigue testing. Results of cyclic deformation characteristic and fatigue damage mechanism have been compared to that in Mn12C1.2 steel. Mn18Cr7N0.6C0.3 steel always shows cyclic softening caused by enhanced planar sliding due to the interaction between N+C and the substitutional atoms as well as the dislocation, which is totally different from cyclic hardening in Mn12C1.2 steel caused by the interaction between C members of C–Mn couples with the dislocation. Enhanced effective stress is obtained due to the solid solution strengthening effect caused by the short range order at low strain amplitude while this effect does not work at high strain amplitude. Internal stress contributes most to the cyclic softening with the increase of strain amplitudes. Significant planar slip characteristic can be observed resulting from low stacking fault energy and high short range order effects in Mn18Cr7N0.6C0.3 steel and finally the parallel or intersecting thin sheets with dislocation tangles separated by dislocation free sheets are obtained with the prolonged cycles under cyclic elastic or plastic strain controlled fatigue testing. There exist amounts of small cracks on the surface of the Mn18Cr7N0.6C0.3 steel because fatigue crack initiation is promoted by the cyclic plastic strain localization. However, the zigzag configuration of the cracks reveals that the fatigue crack propagation is highly inhibited by the planar slip characteristic, which eventually improves the fatigue life.

The crystal structure of polycrystalline powder κ-(BEDT-TTF)2Cu[N(CN)2]Br studied by high energy x-ray diffraction

We present a structural investigation of the organic charge-transfer salt superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br at a temperature of 90 K using high energy (90 keV) powder x-ray diffraction. With this approach we access the scattering profile over a wide range in Q-space (from ~ 0.3 to 19 Å−1). Overall, the observed scattering intensity is understood as a superposition of Bragg diffraction from a crystalline phase superimposed onto a large quasi-amorphous signal, indicative of short range order effects in our powder material. We discuss implications of these findings regarding the structural properties of this material.

First-principles based thermodynamic model of phase equilibria in bcc Fe-Cr alloys

The complete and accurate thermodynamic and kinetic description of any systemis crucialfor understanding and predicting its properties. A particular interest is in systemsthat are used for some practical applications and have to be constantly improved usingmodification of their composition and structure. This task can be quite accuratelysolved at a fundamental level by density functional theory methods. Thesemethods areapplied to two practically important systems Fe-Cr and TiC-ZrC.The elastic properties of pure iron and substitutionally disordered Fe-Cr alloy are investigatedas a function of temperature and concentration using first-principles electronicstructurecalculations by the exact muffin-tin orbitals method. The temperature effectson the elastic properties are included via the electronic, magnetic, and lattice expansioncontributions. It is shown that the degree of magnetic order in both pure iron andFe90Cr10 alloy mainly determines the dramatic change of the elastic anisotropy of thesematerials at elevated temperatures. A peculiarity in the concentration dependence ofthe elastic constants in Fe-rich alloys is demonstrated and related to a change in theFermi surface topology.A thermodynamic model for the magnetic alloys is developed from first principles andapplied to the calculation of bcc Fe-Cr phase diagram. Various contributions to the freeenergy (magnetic, electronic, and phonon) are estimated and included in the model. Inparticular, it is found that magnetic short range order effects are important just abovethe Curie temperature. The model is applied for calculating phase equilibria in disorderedbcc Fe-Cr alloys. Model calculations reproduce a feature known as a Nishizawahorn for the Fe-rich high-temperature part of the phase diagram.The investigation of the TiC-ZrC system includes a detailed study of the defect formationenergies and migration barriers of point defects and defect complexes involvedin the diffusion process. It is found, using ab initio atomistic simulations of vacancymediateddiffusion processes in TiC and ZrC, that a special self-diffusion mechanism isoperative for metal atom diffusion in sub-stoichiometric carbides. It involves a noveltype of a stable point defect, a metal vacancy ”dressed” in a shell of carbon vacancies.It is shown that this vacancy cluster is strongly bound and can propagate through thelattice without dissociating.

X-Ray Absorption Signatures of the Molecular Environment in Water and Ice

The x-ray absorption spectra of water and ice are calculated with a many-body approach for electron-hole excitations. The experimental features, including the effects of temperature change in the liquid, are reproduced from configurations generated by abinitio molecular dynamics. The spectral difference between the solid and the liquid is due to two major short-range order effects. One, due to breaking of hydrogen bonds, enhances the pre-edge intensity in the liquid. The other, due to a nonbonded molecular fraction in the first coordination shell, affects the main spectral edge in the conversion of ice to water. This effect may not involve hydrogen bond breaking as shown by experiment in high-density amorphous ice.

First-principles based calculation of binary and multicomponent phase diagrams for titanium carbonitride

In this paper we have used a combined first principles and Calphad approach to calculate phase diagrams in the titanium–carbon–nitrogen system, with particular focus on the vacancy-induced ordering of the substoichiometric carbonitride phase, TiC x N y ( x + y ≤ 1 ). Results from earlier Monte Carlo simulations of the low-temperature binary phase diagrams are used in order to formulate sublattice models for TiC x N y within the compound energy formalism (CEF) that are capable of describing both the low temperature ordered and the high-temperature disordered state. We parameterize these models using first-principles calculations and then we demonstrate how they can be merged with thermodynamic descriptions of the remaining Ti–C–N phases that are derived within the Calphad method by fitting model parameters to experimental data. We also discuss structural and electronic properties of the ordered end-member compounds, as well as short range order effects in the TiC x N y phase.

Predicting miscibility gaps in reciprocal liquids

There is a strong correlation between the appearance of liquid miscibility gaps in reciprocal phases and the standard Gibbs energy of the reciprocal reaction, Δ°G. The associate solution model does not predict such a correlation but the two-sublattice model does. Physically, the critical temperature of a reciprocal miscibility gap is related to Δ°G and is also affected by the presence of short range order. The latter effect can be estimated from Δ°G using the conformal solution theory which was developed for reciprocal systems with univalent ions. In that approximation the short range order effect is described with a reciprocal parameter. The estimate of that parameter for systems with different valencies is now discussed. The calculated phase diagram may be reasonable for low values of the reciprocal parameter, relative to Δ°G, but is not satisfactory for large values because two asymmetric miscibility gaps will appear when the critical temperature has been suppressed to 3 4 of the value predicted without a reciprocal term. An alternative form of the reciprocal term is now proposed, which does not produce the splitting into two miscibility gaps.

HgL3edge absorption study of theHgBa2CuO4+δsuperconductor

The ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ superconductor has been studied by high resolution Hg ${L}_{3}$ x-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectrum has been simulated by full multiple-scattering calculations in order to explore the origin of different features in the experimental spectrum. The experimental Hg ${L}_{3}$-edge spectrum could be well reproduced by considering a cluster of 85 atoms, containing 10 shells, within a radius of about 7 \AA{} from the central Hg atom. The low energy spectral feature in the XANES spectrum is found to be due to a transition from the Hg p states to the electronic states hybridized with higher shell Ba atoms. This implies that the transition features in the Hg ${L}_{3}$-edge XANES are strongly influenced by medium range order effects unlike the case of ${L}_{3}$ edge of $3d$ transition metals where short-range order is enough to describe the main transition features.

Magnetic characterization of one-dimensional systems composed of nitronylnitroxide radicals as studied by ESR and susceptibility measurements

We synthesized anovd organic radical, 3,4-dichlorophenyl nitronyl nitroxide and characterized magnetic properties in the solid state. An X-ray crystal structure analysis revealed that this molecule formed one-dimensional regular chains in the crystal. Temperature dependence of magnetic susceptibility was reproduced by the antiferromagnetic regular chain model with an exchange interaction J/k B = −8.0 K, which is consistent with the crystal structure. The radical crystal is an example of the regular spin chain in the organic systems that exhibits the largest exchange interaction. Single-crystal cw-ESR exhibited a temperature-dependent shift of g-value. The physical origin of the g-shift is discussed by comparing the observed data with theories describing the short range order effect in antiferromagnetic spin chains. The possibility of demagnetizing field effect on the g-shift in the paramagnetic crystal is also referred

On the oxidation of d-sorbitol on platinum single crystal electrodes: a voltammetric and in situ FTIRS study

The electrooxidation of d-sorbitol on Pt(100), Pt(110), Pt(111) and stepped surfaces vicinal to the (111) pole was studied in perchloric acid medium. The reaction is markedly influenced by the crystalline surface structure. Long range order effects of (111) terraces were also observed. Adsorbed CO (linearly and bridge bonded to the surface, on a level which depends on the electrode surface orientation) was identified by in situ Fourier transform IR (FTIR) spectroscopy as the main poisoning species. Moreover, for Pt(111), glucono-δ-lactone and CO 2 were identified as the main soluble reaction products.

Magnetic susceptibility of Ni(OH) 2 monolayer nanoclusters

DC magnetic susceptibilities χ were measured for Ni(OH) 2 monolayer nanoclusters (Ni-MNC) which were randomly comprised by amorphous SiO 2. The χ showed the Curie–Weiss behavior between about 100 and 300 K, and it deviated from the Curie–Weiss law below about 100 K. The χ-data were compared with the high temperature series expansion (HTSE) theory for 2D Ising ferromagnet, and it was found that the short range order effect in the 2D Ising system was dominant for the magnetism of Ni-MNC between 16 and 100 K. The analysis by the superparamagnetic model showed a gradual increase of the ferromagnetic Ni 2+ cluster size in each Ni-MNC. The quantum size effect in Ni-MNC was also discussed by the modified HTSE theory.

On the oxidation of d-sorbitol on platinum single crystal electrodes: a voltammetric and in situ FTIRS study

The electrooxidation of d-sorbitol on Pt(100), Pt(110), Pt(111) and stepped surfaces vicinal to the (111) pole was studied in perchloric acid medium. The reaction is markedly influenced by the crystalline surface structure. Long range order effects of (111) terraces were also observed. Adsorbed CO (linearly and bridge bonded to the surface, on a level which depends on the electrode surface orientation) was identified by in situ Fourier transform IR (FTIR) spectroscopy as the main poisoning species. Moreover, for Pt(111), glucono-δ-lactone and CO 2 were identified as the main soluble reaction products.

Soliton pinning by long-range order in aperiodic systems.

We investigate propagation of a kink soliton along inhomogeneous chains with two different constituents, arranged either periodically, aperiodically, or randomly. For the discrete sine-Gordon equation and the Fibonacci and Thue-Morse chains taken as examples, we have found that the phenomenology of aperiodic systems is very peculiar: On the one hand, they exhibit soliton pinning as in the random chain, although the depinning forces are clearly smaller. In addition, solitons are seen to propagate differently in the aperiodic chains than on periodic chains with large unit cells, given by approximations to the full aperiodic sequence. We show that most of these phenomena can be understood by means of simple collective coordinate arguments, with the exception of long range order effects. In the conclusion we comment on the interesting implications that our work could bring about in the field of solitons in molecular (e.g., DNA) chains.

Model Calculations of the Structure of Ni-Nb Metallic Glasses

Abstract The partial pair correlation functions of amorphous NixNb100-x alloys (x = 40, 50, 56, and 63) were simulated by computer modelling. A Cluster Relaxation procedure yielded reasonable agree­ ment with the experimental functions when non-additive pair potentials with preference for Ni-Nb atomic pairs were applied. With the use of the Reverse Monte Carlo method perfect agreement could be achieved. The impact of the chemical effect on the short range order is discussed by comparison with a statistical reference cluster. The analysis of the model clusters showed that the chemical short range order effect in amorphous Ni-Nb alloys, increasing with the Ni concentration, does not in­ volve specific stereochemical atomic arrangements. There is no correspondence to the short range order in crystalline Ni3Nb. The structure of Ni-Nb metallic glasses can be described as a polytetra-hedral packing with preferred hetero-coordination.

A comprehensive study of bisulfate adsorption on Pt(111) by radioactive labeling and voltammetry

Adsorption of bisulfate anions on single crystal Pt(111) electrode, ordered and disordered and on polycrystalline platinum has been studied by the use of radioactive labeling method and cyclic voltammetry. The studies have revealed that the saturation surface concentration of bisulfates is 20% higher on the ordered Pt(111) surface than on the polycrystalline electrode. The increased adsorption may most likely be due to a favorable spatial configuration of the anions and surface water molecule networks at the single crystal interface. A consistent model of adsorption on the ordered surface emerges if one assumes that a form of hydrogen exists that is stable at relatively positive electrode potentials, adsorption of which is modified by coadsorbed (bi)sulfate. Available, although not yet direct, evidence is presented which shows that this form of hydrogen is a subsurface hydrogen. The significance of surface geometry and stability in the anomalous voltammetric behavior is discussed vs. that of the long range order effects on the solution side of the Pt(lll) solid-liquid interface.

The magnetic susceptibility of liquid alkali-thallium alloys

The magnetic susceptibility χ M of liquid K-TL and CsTl alloys was measured by the Faraday method. The large negative deviations of χ M from the linear law were found for both systems. The temperature derivatives of χ M, d χM /dT, shows maximum values at about 50 at.%K (or Cs). This indicates the chemical short range order effect in the liquid structure, which may be induced by the transfer of electron from K (or Cs) atom to Tl atom. The negative deviation of χ M from the linear law may be explained by the decrease of mobile electrons.

A further view on the calculation of the enthalpy of cavity formation in liquids. The influence of the cavity size and shape

A reformulation of the Sinanoglu–Reisse semi-empirical approach to describe the cavity formation process in liquids is proposed. The energy of cavity formation is regarded as a strictly potential energy corrected for short range order effects in the liquid state. Deviations from the Corresponding States Principle quantified by the Pitzer acentric factor are considered to describe these short range order effects.The influence of the cavity shape on the calculation of its energetics is emphasized as well as the need for a realistic description of the dependence of the microscopic surface tension on the size and shape of the cavities. The proposed method is successfully applied to binary mixtures of n-alkanes at infinite dilution.

High resolution 1H NMR studies of hydrogen bonding in liquid crystals

Some aspects of hydrogen bonding in liquid crystal phases of p-n-octyloxybenzoic acid have been studied by means of high resolution 1H NMR. The spinning sample technique has been developed for determination of isotropic chemical shifts ( δ ¯ ) of COOH groups in the nematic phase. The discontinuous change of δ at the liquid—nematic transition has been found and interpreted as a short range order effect due to the correlation of cyclic dimers of acid. The temperature dependences of the components of the magnetic shielding tensor of COOH groups have been measured.

A New Effective Ensemble Approach for the Free Energy

AbstractIt is shown that the effective ensemble utilized in Bogolyubov principle may be replaced by new effective ensembles more complete than the former one. That brings some improvements on the approximate thermodynamic function calculations and preserves short range order effects above the critical temperature even if one particle trial Hamiltonian is used.

57Fe M�ssbauer study on compositions of the series Fe3+TaO4-Fe2+Ta2O6

Fe57 Mossbauer spectra were measured on compositions of the series Fe1−x/3Ta1+x/3O4, 0≤x≤1. The spectra are characterized by mixed valencies of Fe2+ and Fe3+ ions for 0 0.5 were fitted using one symmetrical doublet; however, for x<0.5 two symmetrical doublets were necessary to describe these patterns. QS(Fe2+)=2.0–3.2 mm/s and IS(Fe2+)=0.90–1.15 mm/s for all compositions. In the case x<0.5, marked temperature dependent QS values appear to exist. This feature may be related to short range order effects and possibly also in part to intervalence electron transfer betwee Fe2+ and Fe3+ ions.