High-resolution Powder Diffraction Research Articles

Correlation between Cation Disordering and the Anionic Redox Chemistry in Li-Rich Layered Oxides

To satisfy our increasing dependence on the high energy storage electronics, Li-rich layered oxides (Li[LixM1-x]O2, M = Ni, Co, Mn, Ru, Ir, etc) have attracted significant attention as cathode materials for lithium-ion batteries in recent years. This class of cathode materials exhibit promising capacities, up to 300 mAh/g, due to accumulative transition metal and oxygen redox reaction1–5. Additional capacity in this class of Li-rich cathode material is attributed to the anionic redox which is irreversible or partially reversible oxygen evolution6,7 and reversible O2-/n- redox1,3,4,8. Luo el at.1 demonstrated that the localized electron holes on oxygen coordinated by Mn4+ and Li+ ions is promoted by the relatively more ionic interactions of O-(Mn/Li) than O-(Ni/Co) interactions at the result of the oxygen oxidation. In our previous study2, at least partially reversible oxygen evolution was observed in 0.4Li2MnO3-0.6LiMn0.5Ni0.5O2 by using Reitveld refinement of high resolution powder diffraction patterns. In the case of 4d (Ru) and 5d (Ir) transition metal-based Li-rich cathode materials, reversible anionic redox was confirmed by X-ray photoelectron spectroscopy (XPS)3,4. Even though the participation of oxygen in redox activity in Li2MnO3 results in partial oxygen evolution with irreversible structural changes9, oxygen redox reaction is stabilized by the reversible peroxo-dimers (O2 n-) formation in the Li2MO3-based (M = Ru, Ir) Li-rich cathode materials due to the high covalent metal-oxygen environment in Ru- and Ir-based lithium-rich cathode materials. However, Seo et al.10 identified the structural and chemical origin of the anionic redox activity which preferentially takes place along the Li-O-Li configurations (non-bonding O 2p states) in Li-rich layered oxides and cation-disordered oxides by using ab initio calculations based on DFT. The electrons in Li-O-Li states are higher energy than those in the other O 2p states owing to their unhybridized O 2p and Li 2s orbitals without taking into account the covalency between the transition metal and oxygen. Through the significant research efforts, anionic redox mechanism seems to be well established. In the case of Na2RuO3, extra anionic capacity is enabled in honeycomb-ordered Na2RuO3 due to the ordered intermediate Na1RuO3 phase which can accommodate the frontier orbital reorganization11, meanwhile, transition metal migration into the empty Li sites is closely associated with the anionic redox as a result of the structural disordering in Li1.17Ni0.21Co0.08Mn0.54O2 5 and Li2IrxSn1-xO3 systems12. It is still under debating whether such manifold anionic chemistry will be solved in terms of transition metals (3d, 4d, and 5d) or alkali metals (Li and Na) or bulk and local structure. In addition, the different reaction mechanism is confirmed between multivalent iridium redox (Ir4+/5.5+)12 and cumulative iridium (Ir4+/5+) and oxygen (O2-/n-) redox13 even in the same C2/m space group of Li2IrO3 materials.Herein, redox mechanism of Li2IrO3 was investigated as a model compound for Li-rich cathode material to understand the key structural differences that lead to anionic redox activity through the synchrotron-based analysis. The local environment, not the composition itself in Li-rich materials, is one of the major factors affecting the redox reaction. We demonstrate that the in-plane disordering in the transition metal layer play a critical role in cation migration and anionic redox, and that cation migration also can trigger the anionic redox reactions. These fundamental insights about Li-rich material family are critical for further development of anionic redox-based cathode materials. In-plane ordering in pristine state with the same composition of Li2IrO3 has a major impact on cation migration and reversible anion redox. Based on the experimental data, detailed findings and discussion will be presented in the 237th ECS meeting.

Ge-doped Li4Ti5-xGexO12 (x = 0.05) as a fast-charging, long-life bi-functional anode material for lithium- and sodium-ion batteries

We explored the doping effect of Ge4+ on the Li4Ti5-xGexO12 (x = 0.0 and 0.05) anode material by looking at its electrochemical performance in both Li- and Na-ion batteries. Combined analysis using Rietveld refinement of high-resolution powder diffraction (HRPD) and transmission electron microscopy (TEM) unambiguously identified homogeneous Ge doping into the 16c octahedral Ti site of the Li4Ti5O12 (LTO) cubic spinel structure. This Ge doping leads to a much-reduced particle size, slightly expanded lattice and increased electrical conductivity due to the increased Ti3+ to Ti4+ ratio, these results were verified by HRPD, scanning electron microscopy (SEM), 4-point probe and x-ray photoelectron spectroscopy (XPS) analysis. The Li4Ti4.95Ge0.05O12 (Ge0.05-LTO) electrode shows much-improved capacity, high-rate capability and excellent cycling stability in a Li-half cell compared with an un-doped LTO electrode. This performance improvement is due to the reduced Li+ diffusion path and faster Li+ insertion/extraction kinetics that originate from Ge doping. In addition to these results, when tested as an anode for SIBs, the Ge0.05-LTO electrode exhibits enhanced capacity and cycling stability compared to un-doped LTO electrode, demonstrating its bi-functional, advantageous features in both LIB and SIB systems.

Fast continuous measurement of synchrotron powder diffraction synchronized with controlling gas and vapour pressures at beamline BL02B2 ofSPring-8.

A gas- and vapour-pressure control system synchronized with the continuous data acquisition of millisecond high-resolution powder diffraction measurements was developed to study structural change processes in gas storage and reaction materials such as metal organic framework compounds, zeolite and layered double hydroxide. The apparatus, which can be set up on beamline BL02B2 at SPring-8, mainly comprises a pressure control system of gases and vapour, a gas cell for a capillary sample, and six one-dimensional solid-state (MYTHEN) detectors. The pressure control system can be remotely controlled via developed software connected to a diffraction measurement system and can be operated in the closed gas and vapour line system. By using the temperature-control system on the sample, high-resolution powder diffraction data can be obtained under gas and vapour pressures ranging from 1 Pa to 130 kPa in temperatures ranging from 30 to 1473 K. This system enables one to perform automatic and high-throughput in situ X-ray powder diffraction experiments even at extremely low pressures. Furthermore, this developed system is useful for studying crystal structures during the adsorption/desorption processes, as acquired by millisecond and continuous powder diffraction measurements. The acquisition of diffraction data can be synchronized with the control of the pressure with a high frame rate of up to 100 Hz. In situ and time-resolved powder diffraction measurements are demonstrated for nanoporous Cu coordination polymer in various gas and vapour atmospheres.

Neutron Larmor diffraction on powder samples.

A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin-echo small-angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from α-Fe2O3 powder samples. The resulting d-spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample.

Hydrate seeding effect on the metastability of CH4 hydrate

Cyclopentane (CP) hydrate seeds can lead to nucleation of CH4 hydrate with a lower supersaturation; the concept of nucleation potential was applied to estimate the metastable zone width (MSZW) of CH4 hydrate. To verify the crystal structure of CH4 hydrate formed from the CP hydrate seeds, the hydrate samples were analyzed by high resolution powder diffraction (HRPD). 1 wt% of CP hydrates in the system reduced the MSZW of CH4 hydrate from 3.39 K to 1.32 K, and showed synergetic performance with sodium dodecyl sulfate (SDS). From the hydrate nucleation theory, SDS is able to decrease the effective surface energy for heterogeneous nucleation on the stainless steel wall, but the CP hydrate seeds provide new nucleation sites with even lower surface energy than that of the stainless steel wall. Hence, the nucleation rate depends on the amount of CP hydrate seeds, and the kinetic parameter can be estimated from the concentration of nucleation sites on the CP hydrate seeds. Also, the MSZW of CH4 hydrate was satisfactorily correlated with the amount of CP hydrate seeds by the cumulative nucleation potentials using estimated kinetic parameters.

A new CQDs/f-MWCNTs/GO nanocomposite electrode for arsenic (10−12M) quantification in bore-well water and industrial effluents

Strategic combination ofCQDs/f-MWCNTs/GO/GCE for pico-molar arsenic sensing.

Exploring new hydrated delta type vanadium oxides for lithium intercalation.

Three hydrated double layered vanadium oxides, namely Na0.35V2O5·0.8(H2O), K0.36(H3O)0.15V2O5 and (NH4)0.37V2O5·0.15(H2O), were obtained by using mild hydrothermal conditions. Their delta type structural frameworks were solved by high-resolution synchrotron X-ray powder diffraction and the interlayer spacings were interpreted from difference Fourier maps. The inter-slab distances are modulated by the water content and the special arrangements of the alkali and ammonium cations. The XPS measurements denote mixed valence systems with high contents of V4+ ions up to 40%. The monitoring of the V4+ EPR signal over time suggests a reduction of the electronic delocalization on account of the partial oxidation to V5+. The electrochemical performance of the active phases is strongly conditioned by the vacuum-drying process of the electrodes, showing better capacity retention when vacuum is not applied. In situ X-ray diffraction shows a structural mechanism of contraction/expansion of the bilayers upon lithium insertion/extraction where the alkali ions behave as structural stabilizers. Galvanostatic cycling at very low current density implies migration of the alkali "pillars" triggering the collapse of the structure.

Crystal structures and phase relationships in magnetostrictive Tb1−xDyxCo2 system

The crystal structures and phase relationships of Tb1−xDyxCo2 alloys with 0 ⩽ x ⩽ 1 were investigated by synchrotron-based high-resolution x-ray powder diffraction. Three different crystal structures are observed in the system: all the compositions show cubic structure with space group at temperatures above the Curie temperature TC; the Tb-rich side sample shows a rhombohedral structure with space group and the Dy-rich side sample has a tetragonal space group. In situ measurements on the intermediate compound Tb0.3Dy0.7Co2 show a rhombohedral to tetragonal structural transition, and the two phases coexist from 99 K to 111 K, where the so-called magnetic morphotropic phase boundary (MPB) is found. The coexisting phases are believed to induce the anomalous magnetostrictive effect in the MPB regime.

Observation of distinct structural transformation between sI and sH gas hydrates and their kinetic properties during CO2 capture from N2 + CO2

sH hydrate has a deal of attention as an attractive medium of gas storage and separation due to its relatively milder formation condition and higher storage capacity, and thus sH hydrate has focused on the potential application in the post-combustion CO2 capture. Nonetheless, in-depth investigations on the thermodynamic stability of sH hydrate of N2 + CO2 and the possible occurrence of structural transformation during the process have not yet been addressed. Since the gas hydrate-based CO2 capture technology involves stepwise enrichments of CO2 through iterative formation-dissociation processes of CO2 hydrate, knowledge about the thermodynamic stability between sI and sH hydrates in the presence of various N2:CO2 ratios and their kinetic properties is important for designing the gas hydrate-based CO2 separation process. Here, we explored sI and sH hydrates of 3,3-dimethyl-1-butanol + N2 + CO2 focusing on their structural stability and structure-dependent kinetic properties. The experimental data including P–T phase equilibria, induction time, gas uptake, and CO2 separation factor are provided with a structural analysis via synchrotron high-resolution powder diffraction.

Effect of cationic substitutions on the photoluminescence properties of Eu2+ doped SrCN2 prepared by a facile C3N4 based synthetic approach

An alternative general approach to synthesize carbodiimide materials using carbon nitride as precursor is proposed. This new facile synthetic route was illustrated by the preparation of single phases α-SrCN2 and β-SrCN2 in a reproducible and effective manner via the substitution of barium and calcium for strontium. Structural characterizations and optical properties of Eu2+ doped SrCN2 polymorphs were investigated on the bases of high-resolution X-ray powder diffraction and photoluminescence analyses to evaluate the potential of such systems as red phosphors. All Eu2+ doped samples exhibit intense red emission in the 620−630 nm range when excited at 440 nm at 77 K with little impact of the crystal lattice on the emission wavelength. However, calcium and barium substitutions for strontium strongly impact the emission intensity and the emission width respectively and all doped samples have their emission intensity reduced by 50 % around 80−90 K and totally quenched at RT.

Differential Adsorption of l- and d-Lysine on Achiral MFI Zeolites as Determined by Synchrotron X-Ray Powder Diffraction and Thermogravimetric Analysis.

Reported here is the first crystallographic observation of stereospecific bindings of l- and d-lysine (Lys) in achiral MFI zeolites. The MFI structure offers inherent geometric and internal confinement effects for the enantiomeric difference in l- and d-Lys adsorption. Notable differences have been observed by circular dichroism (CD) spectroscopy and thermogravimetric analysis (TGA). Distinct l- and d-Lys adsorption behaviours on the H-ZSM-5 framework have been revealed by the Rietveld refinement of high-resolution synchrotron X-ray powder diffraction (SXRD) data and the density-functional theory (DFT) calculations. Despite demonstrating the approach for l- and d-Lys over MFI zeolites at an atomistic resolution, the differential adsorption study sheds light on the rational engineering of molecular interaction(s) with achiral microporous materials for chiral separation purposes.

Cs2Zn(CN)4: a first example of a non-cyano spinel of composition A2M(CN)4 with A=alkali metal and M=group 12 metal

Abstract The crystal structure of monoclinic Cs2Zn(CN)4 (C2/c, Z = 4) was solved and refined from high-resolution synchrotron powder diffraction data (ESRF: Swiss-Norwegian beamline). In contrast to all other known cyanides of composition A2M(CN)4 with A = alkali metal and M = group 12 metal, which crystallize in cubic or rhombohedrally distorted spinel variants and thus with A+ in an octahedral coordination, the Cs+ cation in Cs2Zn(CN)4 shows an eight-fold coordination by CN− anions of the [Zn(CN)4]2− tetrahedra. Upon heating, no phase transition is observed. Instead, a reversible melting at approx. T = 380°C occurs.

Depicting the crystal structure of fibrous ferrierite from British Columbia using a combined synchrotron techniques approach.

The ferrierite crystal structure has often been subject to discussion because of the possible lowering of symmetry from the space group Immm. It mainly occurs in nature with a fibrous crystal habit, and because of the existence of line/planar defects in the framework, texture and preferred orientation effects it has been difficult to obtain an exact crystallographic model based only on the results from powder diffraction data. Therefore, nano-single-crystal diffraction and tomography data have been combined in order to improve the refinement with a meaningful model. High-quality single-crystal data, providing reliable structural information, and tomography images have been used as input for a Rietveld refinement which took into account a phenomenological description of stacking disorder and the analytical description of the preferred orientation, by means of spherical harmonics for strong texture effects. This is one of the first examples of application of synchrotron nano-diffraction for the structure solution of fibrous minerals of micrometre to nanometre size. The high quality of the crystals allowed collection of single-crystal X-ray diffraction data of up to 0.6 Å resolution, leading to an unambiguous solution and precise anisotropic refinement. Nano-single-crystal diffraction and phase contrast tomography data were collected at ID11 and the high-resolution powder diffraction patterns at ID22 of the European Synchrotron Radiation Facility. This detailed crystallographic characterization provides a basis for understanding the potential of ferrierite for toxicity and carcinogenicity.

Radical Dimerization in a Plastic Organic Crystal Leads to Structural and Magnetic Bistability with Wide Thermal Hysteresis.

The nitroxyl radical 1-methyl-2-azaadamantane N-oxyl (Me-AZADO) exhibits magnetic bistability arising from a radical/dimer interconversion. The transition from the rotationally disordered paramagnetic plastic crystal, Me-AZADO, to the ordered diamagnetic crystalline phase, (Me-AZADO)2, has been conclusively demonstrated by crystal structure determination from high-resolution powder diffraction data and by solid-state NMR spectroscopy. The phase change is characterized by a wide thermal hysteresis with high sensitivity to even small applied pressures. The molecular dynamics of the phase transition from the plastic crystal to the conventional crystalline phase has been tracked by solid-state (1H and 13C) NMR and EPR spectroscopies.

Combining a nine-crystal multianalyser stage with a hybrid CdTe photon-counting detector for high-resolution X-ray powder diffraction at ESRF-ID22

Combining a nine-crystal multianalyser stage with a hybrid CdTe photon-counting detector for high-resolution X-ray powder diffraction at ESRF-ID22

The Effects of External Magnetic Field on the Physical Properties of La<sub>0.41</sub>Ca<sub>0.59</sub>Mn<sub>1-x</sub>Cu<sub>x</sub>O<sub>3</sub> with x = 0.06 and 0.15 in the Temperature Range of 100 – 300 K

Normal 0 false false false EN-US X-NONE X-NONE This work investigated the crystal structure, resistivity and specific heat of La 0.41 Ca 0.59 Mn 1-x Cu x O 3 with x = 0.06 and 0.15. The samples were prepared by a solid reaction method and in milling with high energy milling (HEM) of 700 rpm for ten hours. Neutron scattering with high resolution powder diffraction (HRPD) is used to analyze the phase and crystal structure. For resistivity analysis, four point probes are used, and SQUID Quantum Design is used for specific heat analysis in temperatures range of 100 - 300 K. In all cases, the sample has an orthorhombic crystal structure with a space group Pnma . The influence of a magnetic field on the specific heat and resistivity is also determined as a function of temperature. The resistivity increases in the presence of an external magnetic field. At the temperature less than 184 K, the resisitivity follows the Arhenius model (ln R varies as 1/T 0.25 ) while at higher temperatures it fits the metal-semiconductor model (ln R varies as 1/T). The electronic specific heat parameter γ varies with magnetic field at x = 0.06, but not at x = 0.15. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";}

Topotactic, pressure-driven, diffusion-less phase transition of layered CsCoO2 to a stuffed cristobalite-type configuration.

CsCoO2, featuring a two-dimensional layered architecture of edge- and vertex-linked CoO4 tetrahedra, is subjected to a temperature-driven reversible second-order phase transformation (α → β) at 100 K, which corresponds to a structural relaxation with concurrent tilting and breathing modes of edge-sharing CoO4 tetrahedra. In the present investigation, it was found that pressure induces a phase transition, which encompasses a dramatic change in the connectivity of the tetrahedra. At 923 K and 2 GPa, β-CsCoO2 undergoes a first-order phase transition to a new quenchable high-pressure polymorph, γ-CsCoO2. It is built up of a three-dimensional cristobalite-type network of vertex-sharing CoO4 tetrahedra. According to a Rietveld refinement of high-resolution powder diffraction data, the new high-pressure polymorph γ-CsCoO2 crystallizes in the tetragonal space group I41/amd:2 (Z = 4) with the lattice constants a = 5.8711 (1) and c = 8.3214 (2) Å, corresponding to a shrinkage in volume by 5.7% compared with the ambient-temperature and atmospheric pressure β-CsCoO2 polymorph. The pressure-induced transition (β → γ) is reversible; γ-CsCoO2 stays metastable under ambient conditions, but transforms back to the β-CsCoO2 structure upon heating to 573 K. The transformation pathway revealed is remarkable in that it is topotactic, as is demonstrated through a clean displacive transformation track between the two phases that employs the symmetry of their common subgroup Pb21a (alternative setting of space group No. 29 that matches the conventional β-phase cell).

Study of Kinetics of Solid Phase Transition in Tetracosane С24Н50 by High-Resolution Synchrotron X-Ray Powder Diffraction

Using the small-angle synchrotron X-ray diffraction method at the research facility “BELOK” of the Kurchatov synchrotron radiation source at the NRC Kurchatov Institute, it was shown that the first-order solid phase transition in tetracosane C24H50 passes according to a heterogeneous mechanism in a narrow temperature range ΔT ~ 1 K in accordance with the theory of diffuse phase transitions.

Overcoming chemical equilibrium limitations using a thermodynamically reversible chemical reactor.

All real processes, be they chemical, mechanical or electrical, are thermodynamically irreversible and therefore suffer from thermodynamic losses. Here, we report the design and operation of a chemical reactor capable of approaching thermodynamically reversible operation. The reactor was employed for hydrogen production via the water-gas shift reaction, an important route to 'green' hydrogen. The reactor avoids mixing reactant gases by transferring oxygen from the (oxidizing) water stream to the (reducing) carbon monoxide stream via a solid-state oxygen reservoir consisting of a perovskite phase (La0.6Sr0.4FeO3-δ). This reservoir is able to remain close to equilibrium with the reacting gas streams because of its variable degree of non-stoichiometry and thus develops a 'chemical memory' that we employ to approach reversibility. We demonstrate this memory using operando, spatially resolved, real-time, high-resolution X-ray powder diffraction on a working reactor. The design leads to a reactor unconstrained by overall chemical equilibrium limitations, which can produce essentially pure hydrogen and carbon dioxide as separate product streams.

Ferroic multipolar order and disorder in cyanoelpasolite molecular perovskites.

We use a combination of variable-temperature high-resolution synchrotron X-ray powder diffraction measurements and Monte Carlo simulations to characterize the evolution of two different types of ferroic multipolar order in a series of cyanoelpasolite molecular perovskites. We show that ferroquadrupolar order in [C3N2H5]2Rb[Co(CN)6] is a first-order process that is well described by a four-state Potts model on the simple cubic lattice. Likewise, ferrooctupolar order in [NMe4]2B[Co(CN)6] (B = K, Rb, Cs) also emerges via a first-order transition that now corresponds to a six-state Potts model. Hence, for these particular cases, the dominant symmetry breaking mechanisms are well understood in terms of simple statistical mechanical models. By varying composition, we find that the effective coupling between multipolar degrees of freedom-and hence the temperature at which ferromultipolar order emerges-can be tuned in a chemically sensible manner. This article is part of the theme issue 'Mineralomimesis: natural and synthetic frameworks in science and technology'.