Changes In Unit Cell Dimensions Research Articles

Exploring cycling induced crystallographic change in NMC with X-ray diffraction computed tomography.

This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. The nature of the technique permits the spatial localization of the diffraction information in 3D and mapping of heterogeneities from the electrode to the particle level. An overall decrease of 0.4% and 0.6% was observed for the unit cell volume after 100 cycles for the electrodes cycled to 4.2 and 4.7 V. Additionally, focused ion beam-scanning electron microscope cross-sections indicate extensive particle cracking as a function of upper cut-off voltage, further confirming that severe cycling stresses exacerbate degradation. Finally, the technique facilitates the detection of parts of the electrode that have inhomogeneous lattice parameters that deviate from the bulk of the sample, further highlighting the effectiveness of the technique as a diagnostic tool, bridging the gap between crystal structure and electrochemical performance.

Comparative analysis of ex-situ and operando X-ray diffraction experiments for lithium insertion materials

A comparative study of ex-situ and operando X-ray diffraction techniques using the fast lithium ion conductor Li0.18Sr0.66Ti0.5Nb0.5O3 is presented. Ex-situ analysis of synchrotron X-ray diffraction data suggests that a single phase material exists for all discharges to as low as 0.422 V. For samples discharged to 1 V or lower, i.e. with higher lithium content, it is possible to determine the lithium position from the X-ray data. However, operando X-ray diffraction from a coin cell reveals that a kinetically driven two phase region occurs during battery cycling below 1 V. Through monitoring the change in unit cell dimension during electrochemical cycling the dynamics of lithium insertion are explored. A reduction in the rate of unit cell expansion of 22(2)% part way through the first discharge and 13(1)% during the second discharge is observed. This reduction may be caused by a drop in lithium diffusion into the bulk material for higher lithium contents. A more significant change is a jump in the unit cell expansion by 60(2)% once the lithium content exceeds one lithium ion per vacant site. It is suggested that this jump is caused by damping of octahedral rotations, thus establishing a link between lithium content and octahedral rotations.

Поверхневі напруження на початкових етапах окислення GexSi1-x/Si(001)

Elastic stresses arising at the clean GexSi1−x/Si(001) surface, as well as at the initial stages of its oxidation, are considered qualitatively by analyzing the changes of unit cell dimensions occurring owing to the ad-dimer formation or the atomic or molecular adsorption on the unit cell surfaces. The stress character is found to be almost identical for the clean GexSi1−x/Si(001) surface and the GexSi1−x/Si(001) surface with adsorbed oxygen molecules or one to three adsorbed oxygen atoms. In addition, the surface stresses revealed a significant anisotropy: they turned out compressive along the dimer rows and three times as large as tensile stresses in the perpendicular direction (along the interdimer bonds).

Effect of microfibril twisting on theoretical powder diffraction patterns of cellulose Iβ

Previous studies of calculated diffraction patterns for cellulose crystallites suggest that distortions that arise once models have been subjected to MD simulation are the result of both microfibril twisting and changes in unit cell dimensions induced by the empirical force field; to date, it has not been possible to separate the individual contributions of these effects. To provide a better understanding of how twisting manifests in diffraction data, the present study demonstrates a method for generating twisted and linear cellulose structures that can be compared without the bias of dimensional changes, allowing assessment of the impact of twisting alone. Analysis of unit cell dimensions, microfibril volume, hydrogen bond patterns, glycosidic torsion angles, and hydroxymethyl group orientations confirmed that the twisted and linear structures collected with this method were internally consistent, and theoretical powder diffraction patterns for the two were shown to be effectively indistinguishable. These results indicate that differences between calculated patterns for the crystal coordinates and twisted structures from MD simulation can result entirely from changes in unit cell dimensions, and not from microfibril twisting alone. Although powder diffraction patterns for models in the 81-chain size regime were shown to be unaffected by twisting, suggesting that a modest degree of twist is not inconsistent with experimental data, it may be that other diffraction techniques are capable of detecting this structural difference. Until such time as definitive experimental evidence comes to light, the results of this study suggest that both twisted and linear microfibrils may represent an appropriate model for cellulose Iβ.

Thermal Expansion of Rare‐Earth Pyrosilicates

The use of RE2Si2O7 materials as environmental barrier coatings (EBCs) and in the sintering process of advanced ceramics demands a precise knowledge of the coefficient of thermal expansion of the RE2Si2O7. High‐temperature X‐ray diffraction (HTXRD) patterns were collected on different RE2Si2O7 polymorphs, namely A, G, α, β, γ, and δ, to determine the changes in unit cell dimensions. RE2Si2O7 compounds belonging to the same polymorph showed, qualitatively, very similar unit cell parameters behavior with temperature, whereas the different polymorphs of a given RE2Si2O7 compound exhibited markedly different thermal expansion evolution. The isotropy of thermal expansion was demonstrated for the A‐RE2Si2O7 polymorph while the rest of polymorphs exhibited an anisotropic unit cell expansion with the biggest expansion directed along the REOx polyhedral chains. The apparent bulk thermal expansion coeficcients (ABCTE) were calculated from the unit cell volume expansion for each RE2Si2O7 compound. All compounds belonging to the same polymorph exhibited similar ABCTE values. However, the ABCTE values differ significantly from one polymorph to the other. The highest ABCTE values correspond to A‐RE2Si2O7 compounds, with an average of 12.1 × 10−6 K−1, whereas the lowest values are those of β‐ and γ‐RE2Si2O7, which showed average ABCTE values of ~4.0 × 10−6 K−1.

Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase from Escherichia coli O9a.

WbdD is a bifunctional kinase/methyltransferase that is responsible for regulation of lipopolysaccharide O antigen polysaccharide chain length in Escherichia coli serotype O9a. Solving the crystal structure of this protein proved to be a challenge because the available crystals belonging to space group I23 only diffracted to low resolution (>95% of the crystals diffracted to resolution lower than 4 Å and most only to 8 Å) and were non-isomorphous, with changes in unit-cell dimensions of greater than 10%. Data from a serendipitously found single native crystal that diffracted to 3.0 Å resolution were non-isomorphous with a lower (3.5 Å) resolution selenomethionine data set. Here, a strategy for improving poor (3.5 Å resolution) initial phases by density modification and cross-crystal averaging with an additional 4.2 Å resolution data set to build a crude model of WbdD is desribed. Using this crude model as a mask to cut out the 3.5 Å resolution electron density yielded a successful molecular-replacement solution of the 3.0 Å resolution data set. The resulting map was used to build a complete model of WbdD. The hydration status of individual crystals appears to underpin the variable diffraction quality of WbdD crystals. After the initial structure had been solved, methods to control the hydration status of WbdD were developed and it was thus possible to routinely obtain high-resolution diffraction (to better than 2.5 Å resolution). This novel and facile crystal-dehydration protocol may be useful for similar challenging situations.

Synthesis and properties of iridium-doped hematite (α-Fe2O3)

The effect of the incorporation of Ir3+ ions on the properties of α-Fe2O3 formed by dehydroxylation of α-FeOOH was investigated using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), 57Fe Mössbauer, UV–Vis–NIR and FT-IR spectroscopies, SQUID magnetometer, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Pure and Ir-doped hematite samples were obtained by heating of pure and Ir-doped goethites (α-FeOOH) formed by precipitation from mixed Fe(III)–Ir(III) chloride solutions in a highly alkaline medium. The incorporation of Ir3+ ions into the α-Fe2O3 structure led to changes in unit-cell dimensions, crystallinity, particle size and shape, as well as changes in the magnetic, infrared and UV–Vis properties. An increase in the temperature of the Morin transition with an increase in Ir-doping was observed by Mössbauer spectroscopy and magnetic measurements.

Thermal expansion of lanthanum silicate oxyapatite (La9.33+2x(SiO4)6O2+3x), lanthanum oxyorthosilicate (La2SiO5) and lanthanum sorosilicate (La2Si2O7)

Four types of powder specimens of La9.33(SiO4)6O2 (space group P63/m and Z=1), La9.33+2x(SiO4)6O2+3x with 0.06≤x≤0.13 (P63/m and Z=1), La2SiO5 (P21/c and Z=4) and La2Si2O7 (P21/c and Z=4) were examined by high-temperature X-ray powder diffractometry to determine the changes in unit-cell dimensions up to 1473K. The anisotropy of thermal expansion was demonstrated for the former two crystals to clarify the thermal behaviors of the highly c-axis-oriented polycrystals. With La9.33(SiO4)6O2, the linear expansion coefficient of the a-axis (αa) was 4.8×10−6K−1 and that of the c-axis (αc) was 1.8×10−6K−1 in the temperature range from 298 to 1473K. The αa- and αc-values of La9.33+2x(SiO4)6O2+3x (0.06≤x≤0.13) were, respectively, 5.9×10−6K−1 and 2.3×10−6K−1. The coefficients of mean linear thermal expansion were 4.9×10−6K−1 for La2SiO5 and 6.0×10−6K−1 for La2Si2O7, which describe the thermal expansion behaviors of the randomly grain-oriented polycrystalline materials.

The effect of iridium(III) ions on the formation of iron oxides in a highly alkaline medium

The effect of the presence of Ir 3+ ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), 57Fe Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Monodispersed lath-like α-FeOOH (goethite) particles precipitated by hydrothermal treatment in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. The presence of Ir 3+ ions in the precipitation system strongly influenced the phase composition, magnetic, structural and morphological properties of obtained samples. The formation of α-Fe 2O 3 (hematite) along with α-FeOOH in the first stage of hydrothermal treatment and the transformation of α-FeOOH and α-Fe 2O 3 to Fe 3O 4 (magnetite) by a longer hydrothermal treatment was caused by the presence of Ir 3+ ions. Ir 3+ for Fe 3+ substitution in the structure of α-FeOOH brought about changes in unit-cell dimensions, crystallinity, particle size and shape, hyperfine magnetic field and infrared bands positions. Ir 3+ for Fe 3+ substitution in the structure of α-Fe 2O 3 led to an increase in the temperature of the Morin transition; Mössbauer spectroscopy showed the presence of α-Fe 2O 3 in the antiferromagnetically ordered state at 293 K.

Role of Ti 4+ and Sn 4+ ions in spinel formation and reactive sintering of magnesia-rich ceramics

The solid solubility of magnesia in magnesium aluminate spinel and magnesium aluminate spinel in magnesia does not change with temperature thus not creating bonds or precipitation over periclase grains in a single stage sintering process. In comparison, the precipitated spinels in magnesia-chromia refractories form complex spinel due to inversion in the position of bivalent and trivalent cations within the structure, making them more stable at high temperature than either normal or inverse spinel. Additives form low-temperature compounds that diffuse into the spinel structure and create defects that change the properties of spinel solid solution. In the present study, magnesia and alumina powders along with tetravalent oxide additives were analyzed for their role in reactive densification of spinel in a single stage firing process in order to achieve a better binding system for magnesia-based refractories. These tetravalent oxides on reaction with magnesia form spinel solid solution with MgAl 2O 4 as they have similar crystal structure. The spinel solid solution formed using oxide additives is expected to have higher solubility in magnesia than magnesium aluminate spinel, resulting in improvement of the bonding during sintering through increased in solid solubility at elevated temperatures followed by precipitation of secondary spinel phases, similar to the complex spinel in magnesia-chrome refractories. The formation of spinel during firing remains as a second phase that retards the grain growth of periclase. The changes in unit cell dimensions with temperature and amount of additive were analyzed using Reitveld method and correlated with the densification behaviour at different temperatures.

Structural, magnetic and superconducting phase transitions in CaFe 2As 2 under ambient and applied pressure

At ambient pressure CaFe 2As 2 has been found to undergo a first order phase transition from a high temperature, tetragonal phase to a low-temperature orthorhombic/antiferromagnetic phase upon cooling through T ∼ 170 K. With the application of pressure this phase transition is rapidly suppressed and by ∼0.35 GPa it is replaced by a first order phase transition to a low-temperature collapsed tetragonal, non-magnetic phase. Further application of pressure leads to an increase of the tetragonal to collapsed tetragonal phase transition temperature, with it crossing room temperature by ∼1.7 GPa. Given the exceptionally large and anisotropic change in unit cell dimensions associated with the collapsed tetragonal phase, the state of the pressure medium (liquid or solid) at the transition temperature has profound effects on the low-temperature state of the sample. For He-gas cells the pressure is as close to hydrostatic as possible and the transitions are sharp and the sample appears to be single phase at low temperatures. For liquid media cells at temperatures below media freezing, the CaFe 2As 2 transforms when it is encased by a frozen media and enters into a low-temperature multi-crystallographic-phase state, leading to what appears to be a strain stabilized superconducting state at low temperatures.

An isosymmetric phase transition of orthopyroxene found by high-temperature X-ray diffraction

High-temperature synchrotron X-ray powder diffraction experiments for the composition of (Ca 0.06 Mg 1.94 )Si 2 O 6 have been carried out in the present study to clarify whether orthopyroxene has a transition between low- and high-temperature phases. Our results show that discontinuous changes of unit-cell dimensions and volume occur at 1170 °C during both heating and cooling processes and that the space group of Pbca does not change during this reversible phase transition. These facts indicate a first-order and isosymmetric phase transition. This high-temperature phase is thermodynamically distinct from the low-temperature phase, i.e., orthoenstatite in the Mg-rich portion of Mg 2 Si 2 O 6 -CaMgSi 2 O 6 phase diagram, although they have the same space group.

Electron backscatter diffraction analysis of zircon: A systematic assessment of match unit characteristics and pattern indexing optimization

Quantitative microstructural analysis of zircon using electron backscatter diffraction (EBSD) requires a comparison of empirically collected electron backscatter patterns with theoretical patterns or “match units” derived from known crystallographic parameters. There are 23 possible crystallographic data sets for zircon, and associated match units, derived from natural and synthetic zircon and from theoretical calculations over a range of pressures and different rare earth element (REE) compositions. A systematic assessment of these match units has been undertaken by EBSD analysis of each of four zircons from a range of geological environments combined with principal components analysis and self-organizing map networks. Comparison of the different match units shows a systematic relationship across all samples that are related to changes in unit-cell dimensions associated with pressure and compositional variations. Systematic variations in the data generated from 96 EBSD maps, each comprising 10 000 electron backscatter patterns, indicate that match units associated with increasing pressure or REE dopants yield poorer quality EBSD data. The match units from low-pressure, undoped, natural zircon consistently yield the best EBSD results and are recommended for natural zircon EBSD studies irrespective of the zircon source or U content. The results provide a clear strategy for optimizing the acquisition and analysis of EBSD data from zircon from both crustal and mantle sources. In addition, the developed approach to match unit analysis may be applied to all other crystalline materials, potentially optimizing EBSD analyses from a range of materials.

In Situ Synchrotron Powder X-ray Diffraction Studies of the Thermal Decomposition of β- and γ-AlD3

Details of the thermal decomposition of β-AlD3 and γ-AlD3 have been investigated by in situ synchrotron X-ray diffraction at a constant heating rate of 1 K/min and isothermally in dynamical vacuum. The β-AlD3 transforms into α-AlD3 prior to decomposing to Al and D2. The transformation into α-AlD3 starts at about 80 °C, and the decomposition to Al and release of D2 starts at 130 °C. The transformation of γ-AlD3 into α-AlD3 starts at about 90 °C, and the sample decomposes to Al and D2 at a higher temperature (from about 130 °C). From about 110 °C, γ-AlD3 also decomposes directly into Al and D2. Detailed analyses of the changes in unit cell dimensions during the decomposition for all phases have been performed in order to propose possible routes for the transitions.

The crystal structure of ammoniojarosite, (NH4)Fe3(SO4)W(OH)6and the crystal chemistry of the ammoniojarosite–hydronium jarosite solid-solution series

AbstractThe atomic structure of ammoniojarosite,[(NH4)Fe3(SO4)2(OH)6], a = 7.3177(3) Å, c = 17.534(1) Å, space groupRm,Z= 3, has been solved using single-crystal X-ray diffraction (XRD) towR3.64% and R 1.4%. The atomic coordinates of the hydrogen atoms of the NH4group were located and it was found that the ammonium group has two different orientations with equal probability. Hydronium commonly substitutes into jarosite group mineral structures and samples in the ammoniojarosite–hydronium jarosite solid-solution series were synthesized and analysed using powder XRD and Rietveld refinement. Changes in unit-cell dimensions and bond lengths are noted across the solidsolution series. The end-member ammoniojarosite synthesized in this study has no hydronium substitution in theAsite and the unit-cell dimensions determined have a smaller a dimension and larger c dimension than previous studies. Two natural ammoniojarosite samples were analysed and shown to have similar unit-cell dimensions to the synthetic samples. Short-wave infrared and Fourier transform infrared spectra were collected for samples from the NH4–H3O jarosite solid-solution series and the differences between the end-members were significant. Both are useful tools for determining NH4content in jarosite group minerals.

An investigation of Cu(II) adsorption by raw and acid-activated bentonite: A combined potentiometric, thermodynamic, XRD, IR, DTA study

Adsorption of Cu(II) by raw bentonite (RB) and acid-activated bentonite (AAB) samples was investigated as a function of the initial Cu(II) concentration, solution pH, ionic strenght, temperature, the competitive and complexation effects of ligands (Cl −, SO 4 2−, PO 4 3−). Langmuir monolayer adsorption capacity of the RB (42.41 mg g −1) was found greater than that of the AAB (32.17 mg g −1). The effect of structural charges on the reactivity of the edge groups was evidenced by the particular proton adsorption behaviour of the bentonite samples. The spontaneity of the adsorption process is established by decrease in Δ G which varied from −0.34 to −0.71 kJ mol −1 (RB), −1.13 to −1.49 kJ mol −1 (AAB) in temperature range 303–313 K. Infrared (IR) spectra of the bentonite samples showed that the positions and shapes of the fundamental vibrations of the OH and Si–O groups were influenced by the adsorbed Cu(II) cations. Differential thermal analysis (DTA) results showed that adsorbed Cu(II) cations have a great effect on the thermal behaviour of the bentonite samples. The X-ray diffraction (XRD) spectra indicated that the Cu(II) adsorption onto the bentonite samples led to changes in unit cell dimensions and symmetry of the parent bentonites.

TiCl3-Enhanced NaAlH4: Impact of Excess Al and Development of the Al1-yTiy Phase during Cycling

NaAlH(4) with TiCl(3) and Al were mixed by ball-milling and cycled three times. The hydrogen storage properties were monitored during cycling, and the products were characterized by synchrotron X-ray diffraction. Because of the previously described formation of Al(1)(-)(y)Ti(y) with y approximately 0.15 during cycling that traps Al beyond the amount associated with the formation of NaCl, some Na(3)AlH(6) has no free Al to react with to form NaAlH(4). This was counteracted in the present work by adding a stoichiometric amount of Al that increases the theoretical storage capacity. Due to limitations in metal diffusion small amounts of Na(3)AlH(6) were still detected. When approximately 7 mol % more Al than the stoichiometric amount was added, the observed storage capacity increased significantly, and the Na(3)AlH(6) content was negligible after prolonged rehydrogenation. Cycled NaAlH(4) + 10 mol % TiCl(3) were desorbed to two different levels, and the diffraction patterns were compared. There is no change in unit-cell dimensions during desorption, and there is no sign of changes in the bulk composition of the Al(1)(-)(y)Ti(y) phase during a cycle. Adding pure Ti to a NaH + Al mixture by ball-milling in argon or hydrogen results in formation of TiH(2) that is stable during at least one cycle.

An examination of the thermal expansion of urea using high-resolution variable-temperature X-ray powder diffraction

Variable-temperature high-resolution capillary-mode powder X-ray diffraction is used to assess changes in unit-cell dimensions as a function of temperature over the range 188–328 K. No evidence was found for any polymorphic transformations over this temperature range and thermal expansion coefficients for urea were found to be αa= (5.27 ± 0.26) × 10−5 K−1and αc= (1.14 ± 0.057) × 10−5 K−1.

Ikaite (CaCO3.6H2O) compressibility at high water pressure: a synchrotron X-ray diffraction study

AbstractIkaite (CaCO3.6H2O), which forms in cold carbonate-rich marine environments, also crystallizes from calcite under aqueous conditions above ∼0.5 GPa at room temperature. Using synchrotron X-ray powder diffraction, measurements have been made of pressure-induced changes in unit-cell dimensions of ikaite contained in a diamond anvil cell. Ikaite shows anisotropic compressibility along the crystallographic axes in the order a > c > b up to 4 GPa. Comparison with other phases shows the relative volume compressibility of ikaite to be greater than that of gypsum (CaSO4.2H2O), calcite and aragonite. The volume of ikaite is less than that occupied by equivalent volumes of CaCO3 (calcite/aragonite) + 6H2O at all pressures below the freezing point (H2O(l) to ice VI). The bulk modulus of ikaite has been obtained from a fit to the Vinet equation of state, giving V0 = 760.3±0.1 Å3, K0 = 21.3±1.4 GPa, and K0' = 11.7±1.7. Dissolution of CaCO3 in H2O (l) at high pressure resulting in crystallization of CaCO3.6H2O suggests equilibrium behaviour between a carbonate-rich fluid species and the condensed hydrated calcium carbonate. The potential for ikaite as a candidate phase for water transport in cold subduction zones is considered.

Proton positions in spinel H 0.9Li 0.1[Li 0.33Ti 1.67]O 4, an ion-exchanged spinel Li 1[Li 0.33Ti 1.67]O 4

Spinel Li 1[Li 0.33Ti 1.67]O 4 is an attractive candidate for the use as anode material in Li-ion batteries. This work focusses on the structural changes of spinel Li 1[Li 0.33Ti 1.67]O 4 upon the exchange of Li-ions with protons leading to the composition H 0.9Li 0.1[Li 0.33Ti 1.67]O 4. The structure has been determined by means of Fourier density difference analysis of neutron diffraction data on the protonated material, collected over a wide range of d-spacings with high counting statistics. The protons replace the Li-ions on the crystallographic 8a sites, and also occupy a fraction of the 48f sites that are located in the same ab-plane as the 8a sites. These positions suggest that the protons prefer to be located near the oxygen atoms. Based on these results, a strong influence on the properties as Li-ion battery electrode material may be anticipated. The small change in unit-cell dimension and the considerable amount of hydrogen that can be hosted in spinel Li 1[Li 0.33Ti 1.67]O 4 are favorable for the use as fuel-cell electrolyte material.