X-ray Powder Diffraction Experiments Research Articles

CuFeS2 as a Very Stable High-Capacity Anode Material for Sodium-Ion Batteries: A Multimethod Approach for Elucidation of the Complex Reaction Mechanisms during Discharge and Charge Processes.

Highly crystalline CuFeS2 containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g-1 increases to 512 mAh g-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g-1 at 0.5 A g-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and 23Na NMR and Mössbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS2, nanocrystalline NaCuFeS2 is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu+ is reduced to nanocrystalline Cu, while nanocrystalline Na2S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS2. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline CuxS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu2S, and Cu7.2S4 appeared in the discharged state, while NaF and Cu5FeS4 are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

4f-3d interaction dominated field tailoring spin switching in rare earth doped Dy0.5Er0.5FeO3 single crystal

A large single crystal Dy0.5Er0.5FeO3 of 5.2 mm in diameter and 55 mm in length is prepared using the optical floating zone furnace system. The good quality of the single crystal without impurities is confirmed by powder and Laue X-ray diffraction experiments. Magnetic measurements are conducted using 1~2 millimeter cubic sample of Dy0.5Er0.5FeO3 single crystal, which experiences spin switching in two measurement modes of zero-field-cooling (ZFC) and field-cooling (FC) magnetization vs temperature (M-T) curves under magnetic fields less than 48 Oe. The co-occurrence of spin switching (i.e. magnetization drop in FC mode and magnetization jump in ZFC mode) has not been reported in the parent materials of DyFeO3 and ErFeO3 single crystals. More interestingly this kind of spin switching can be easily tailored by using low fields in a large temperature range from below 50 K to nearly 400 K. Spin reorientation transition occurs near 35.9-48 K, where the spin configuration of the iron sublattice changes from Γ4 and Γ2. The magnetic interaction between (Dy, Er)-4f and Fe-3d electrons in the two different sublattices of Dy0.5Er0.5FeO3 single crystal which governs the spin reorientation transition and spin switching under different temperature and magnetic field are discussed.

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)*.

The switching mechanism of the flexible framework Zn4O(benztb)1.5 (benztb=N,N,N’,N’‐benzidine tetrabenzoate), also known as DUT‐13, was studied by advanced powder X‐ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n‐butane (273 K) shed light on the hitherto unnoticed guest‐induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm3 g−1 in the open‐pore phase to 0.91 cm3 g−1 in the contracted‐pore phase. The high temperature limit for adsorption‐induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT‐13 framework is softer than other mesoporous MOFs like DUT‐49 and does not support the formation of overloaded metastable states required for negative gas‐adsorption transitions.

Effects of a Clean Subcritical Degreasing System on Wool Fibers

It makes sense to use environmentally friendly methods of degreasing in fur-making process. In this study, subcritical n-pentane was used to degrease wool fibers. Thermogravimetric analysis (TGA) was used to observe and analyze the properties of the subcritical n-pentane degreased wool fibers. The results showed that the thermal stability of the fibers increased. Fourier Transform Infrared (FTIR) spectroscopy was used to analyze the structural changes of macromolecular chains in wool fibers. It was found that when the pressure was higher than 0.4 MPa, the wool fibers underwent a conformational change with the α-helix changing to β-folding. If the pressure was as high as 0.6 MPa, the disulfide bonds in the wool fibers scale layer appeared to break. X-ray powder diffraction experiment was used to study changes in wool fiber aggregation morphology. It was demonstrated that the crystalline zone of wool fibers changed and the fibers index grew, from 22.89% to 30.19%. Field emission scanning electron microscopy and ultra-depth of field microscopy was used to analyze changes in the surface morphology of wool fibers. The results suggested that after the treatment, the wool fibers were not damaged and the impurities on the wool surface were reduced.

High-pressure monoclinic–monoclinic transition in fergusonite-type HoNbO4

In this paper we perform a high-pressure (HP) study of fergusonite-type HoNbO4. Powder x-ray diffraction experiments and ab initio density-functional theory (DFT) simulations provide evidence of a phase transition at 18.9(1.1) GPa from the monoclinic fergusonite-type structure (space group I2/a) to another monoclinic polymorph described by space group P21/c. The phase transition is reversible and the HP structural behavior is different than the one previously observed in related niobates. The HP phase remains stable up to 29 GPa. The observed transition involves a change in the Nb coordination number from 4 to 6, and it is driven by mechanical instabilities. We have determined the pressure dependence of unit-cell parameters of both phases and calculated their room-temperature equation of state. For the fergusonite-phase we have also obtained the isothermal compressibility tensor. In addition to the HP studies, we report ambient-pressure Raman and infrared (IR) spectroscopy measurements. We have been able to identify all the active modes of fergusonite-type HoNbO4, which have been assigned based upon DFT calculations. These simulations also provide the elastic constants of the different structures and the pressure dependence of the Raman and IR modes of the two phases of HoNbO4. According to ab initio calculations, the reported phase transition is related to a mechanical instability and a phonon softening.

High-pressure structural systematics in neodymium up to 302 GPa

Angle-dispersive x-ray powder diffraction experiments have been performed on neodymium metal to a pressure of 302 GPa. Up to 70 GPa we observe the $hP4\ensuremath{\rightarrow}cF4\ensuremath{\rightarrow}hR24\ensuremath{\rightarrow}oI16\ensuremath{\rightarrow}hP3$ transition sequence reported previously. At 71(2) GPa we find a transition to a phase which has an orthorhombic structure ($oF8$) with eight atoms in the unit cell, space group $Fddd$. This structure is the same as that recently observed in samarium above 93 GPa, and is isostructural with high-pressure structures found in the actinides Am, Cf, and Cm. We see a further phase transition at 98(1) GPa to a phase with the orthorhombic $\ensuremath{\alpha}$-U ($oC4$) structure, which remains stable up to 302 GPa, the highest pressure reached in this study. Electronic structure calculations find the same structural sequence, with calculated transition pressures of 66 and 88 GPa, respectively, for the $hP3\ensuremath{\rightarrow}F8$ and $oF8\ensuremath{\rightarrow}oC4$ transitions. The calculations further predict that $oC4$-Nd loses its magnetism at 100 GPa, in agreement with previous experimental results, and it is the accompanying decrease in enthalpy and volume that results in the transition to this phase. Comparison calculations on the $oF8$ and $oC4$ phases of Sm show that they both retain their magnetism to at least 240 GPa, with the result that $oC4$-Sm is calculated to have the lowest enthalpy over a narrow pressure region near 200 GPa at 0 K.

Building Block Symmetry Relegation Induces Mesopore and Abundant Open-Metal Sites in Metal–Organic Frameworks for Cancer Therapy

Building Block Symmetry Relegation Induces Mesopore and Abundant Open-Metal Sites in Metal–Organic Frameworks for Cancer Therapy

Hydrothermal synthesis and crystal structures of a novel Keggin-type polyoxometalate based on 1,10-phenanthroline

Herein a novel inorganic-organic hybrid Keggin-type heteropolymolybdate [Ni2Na(C12H8N2)4(BMo12O40)(H2O)2] (1) has been synthesized under hydrothermal conditions in aqueous solution. The cyrstal structure was fully characterized by powder X-ray diffraction (XRD), elemental analysis, Fourier-tranform infrared spectrum (FT-IR), Thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM) analysis. Single crystal X-ray structural analysis demonstrates that the complex consists of a Keggin anion [BMo12O40]5− polyanion, four 1,10-phenanthroline (C12H8N2) ligands, two Ni(II) ions, two Na(I) ions and two aqua ligands. The experimental powder X-ray diffraction (XRD) result of the crystal is consistent with the calculated data. The SEM image shows that the compound crystals have a cubic structure.

New perspectives in macromolecular powder diffraction using single-photon-counting strip detectors: high-resolution structure of the pharmaceutical peptide octreotide.

Advances in instrumentation, as well as the development of powerful crystallographic software have significantly facilitated the collection of high-resolution diffraction data and have made X-ray powder diffraction (XRPD) particularly useful for the extraction of structural information; this is true even for complex molecules, especially when combined with synchrotron radiation. In this study, in-line with past instrumental profile studies, an improved data collection strategy exploiting the MYTHEN II detector system together with significant beam focusing and tailored data collection options was introduced and optimized for protein samples at the Material Science beamline at the Swiss Light Source. Polycrystalline precipitates of octreotide, a somatostatin analog of particular pharmaceutical interest, were examined with this novel approach. XRPD experiments resulted in high angular and d-spacing (1.87 Å) resolution data, from which electron-density maps of enhanced quality were extracted, revealing the molecule's structural properties. Since microcrystalline precipitates represent a viable alternative for administration of therapeutic macromolecules, XRPD has been acknowledged as the most applicable tool for examining a wide spectrum of physicochemical properties of such materials and performing studies ranging from phase identification to complete structural characterization.

Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X-Ray Diffraction Protocol.

Structurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure‐function relations and enable functional material design. Herein, a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X‐ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.

Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X‐Ray Diffraction Protocol

AbstractStructurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure‐function relations and enable functional material design. Herein, a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X‐ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.

A Comprehensive Study of Ca9Tb(PO4)7 and Ca9Ho(PO4)7 Doped β-Tricalcium Phosphates: Ab initio Crystal Structure Solution, Rietveld Analysis, and Dielectric Properties

The scientific interest toward the structural, luminescence, and dielectric properties of tricalcium phosphate (TCP) materials, in particular, the doped TCP-based compounds, is mainly due to their biocompatibility and bioactivity behavior and the increasing number of their applications. In the literature, structural investigations of a doped β-TCP compound are usually carried out by powder diffraction data under the assumption that it has a centrosymmetric whitlockite structure. Recent studies have shown that this assumption is not always fulfilled. For this reason, it is necessary to use methods of nonlinear and dielectric spectroscopy to prove the true symmetry of whitlockite-like phases. This work provides a detailed and comprehensive study on the structural, dielectric, and nonlinear properties of the polycrystalline Tb- and Ho-doped tricalcium phosphates, chemically Ca9Tb(PO4)7 and Ca9Ho(PO4)7. Their crystal structure was explored using powder X-ray diffraction, adopting an ab initio approach for the structure solution followed by the Rietveld refinement. For Ca9Tb(PO4)7, the qualitative analysis of the experimental powder X-ray diffraction pattern revealed that the sample was not a single phase. Nevertheless, its crystal structure has been determined by Direct Methods. The presence of the dopant cation was omitted in the solution process by Direct Methods and considered in the successive Rietveld refinement step. The analysis of the occupancies has clarified the Tb3+ cation distribution in its preferential sites. The same pathway has been followed for the Ca9Ho(PO4)7 sample, which corresponded to a single-phase structure. The dielectric properties of the two doped compounds (Tb3+ and Ho3+) were also examined, and reversible ferroelectric-paraelectric phase transitions were found at 862 and 872 K, respectively.

Unmixing multiple metamorphic muscovite age populations with powder X-ray diffraction and 40Ar/39Ar analysis

A combination of modal estimates from powder X-ray diffraction (XRD) experiments and argon isotopic data shows that muscovite ⁴⁰Ar/³⁹Ar total gas age correlates with muscovite composition near the retrograde Bald Mountain shear zone (BMSZ) in Claremont, New Hampshire, and that the shear zone was active at ∼245 Ma. Petrologic study demonstrates that chemical disequilibrium is preserved in muscovite grains in these samples. The recognition of this preservation is critical to the interpretation of the ⁴⁰Ar/³⁹Ar step-heating experiments, which never produce age plateaus and yield spectra with steps that range in age by ∼20 Ma. Petrographic, compositional, and crystallographic data all indicate that the age spectra reflect dissolution of metastable Na-rich muscovite and precipitation of stable Na-poor muscovite associated with deformation in the BMSZ.Comparison of whole rock and muscovite concentrate XRD patterns from individual samples demonstrates that the mineral separation process can fractionate these muscovite populations. Therefore, four muscovite concentrates of varying magnetic susceptibility were prepared from a single hand sample, analyzed by XRD, and dated. These four splits define a mixing line that resolves end-member ages of 244.5 ± 4.2 Ma and 302.5 ± 12.5 Ma (1σ). Although the ages are imprecise, the petrologically supported conclusion that these schists preserve two discrete ages is distinct from an interpretation that the spectra reflect cooling through closure at ∼270 Ma, as might be concluded in the absence of petrologic characterization. The XRD results also demonstrate that, even well above anchizone conditions, petrologic information relevant to ⁴⁰Ar/³⁹Ar dating is observable in subtle variations in the crystallography of muscovite grains.

Highly Selective Separation of Isopropylbenzene and α-Methylstyrene by Nonporous Adaptive Crystals of Perbromoethylated Pillararene via Vapor- and Liquid-Phase Adsorptions

Isopropylbenzene (IPB) and α-methylstyrene (AMS), two members of C9 aromatics, are important in both industrial production and laboratory research, but the separation of IPB/AMS mixtures is still a big challenge. Here, we provide a new strategy to separate IPB and AMS using nonporous adaptive crystals of four pillararenes, perethylated pillar[5]arene, perethylated pillar[6]arene, perbromoethylated pillar[5]arene, and perbromoethylated pillar[6]arene (BrP6). Among them, BrP6 selectively adsorbs IPB from an equal volume mixture of IPB and AMS with >95% purity for solid-vapor phase adsorption and >94% purity for solid-liquid phase adsorption, while the selectivities for the other three pillararenes are unsatisfactory. Single-crystal structural analyses combined with powder X-ray diffraction and differential scanning calorimetry experiments demonstrate that the selectivity arises from the different stabilities of guest-loaded BrP6 crystals. Moreover, the reversible transitions between guest-free and IPB-loaded structures indicate the preeminent recycling performance of BrP6 crystals.

Alkynyl-Based sp 2 Carbon-Conjugated Covalent Organic Frameworks with Enhanced Uranium Extraction from Seawater by Photoinduced Multiple Effects

Biofouling is a major obstacle to the efficient extraction of uranium from seawater due to the numerous marine microorganisms in the ocean. Herein, we report a novel amidoxime (AO) crystalline cova...

On the structural complexity of tetragonal tungsten bronze type niobium tungsten oxides

AbstractIn this comparative study, two samples with a slightly different oxygen : metal ratio have been characterized by various electron microscopy methods and by single‐crystal and powder X‐ray diffraction (XRD). A reasonably good fit to the experimental powder XRD patterns could be achieved by Rietveld refinement for both samples Nb8W9O47 and Nb7W10O47.5 using the structural models of Nb6.7W10.3O47 and Nb8W9O47 both obtained from X‐ray crystal structure analysis. HRTEM investigations confirm that Nb8W9O47 crystallizes as a pure phase in the well‐known threefold superstructure of the tetragonal tungsten bronze type (TTB). In contrast, a more complex real structure was found for the sample Nb7W10O47.5 with small domains of Nb4W7O31 appearing besides large ones of Nb8W9O47 and in addition extended TTB‐based areas with short‐range order only. The diffuse scattering caused by this disorder is easily detected in the electron diffraction pattern but does not affect the Rietveld refinement of the powder XRD patterns. However, on the basis of powder diffraction experiments, it is clearly possible to distinguish between the above compounds and the hypothetical, but non‐existing compound “Nb18W16O93”, a composition recently postulated for battery materials.

Non-innocent Intercalation of Diamines into Tetragonal FeS Superconductor

We report two solvothermal pathways toward intercalated iron sulfide, [Fe8S10]Fe(en)3·en0.5 (en = ethylenediamine), featuring [Fe8S10]2– layers stacked by [Fe(en)3]2+ cations and free ethylenediamine molecules. [Fe8S10]Fe(en)3·en0.5 is synthesized in a simple single-step method from Fe and S in ethylenediamine with addition of NH4Cl mineralizer as well as from solvothermal treatment of mackinawite, tetragonal FeS. In situ synchrotron powder X-ray diffraction experiments reveal a clear transformation of tetragonal FeS into [Fe8S10]Fe(en)3·en0.5 upon reaction with ethylenediamine. In-house control synthetic experiments confirmed the chemical process, whereby ethylenediamine leaches iron solely from the tetragonal Fe–S layers to form [Fe(en)3]2+ complexes and thereby oxidize the intralayer iron to Fe2.25+. Our report emphasizes that, in layered iron chalcogenides, diamines can intercalate as charged coordination complexes in tandem with neutral diamine molecules.

Regulating the Nb2C nanosheets with different degrees of oxidation in water lubricated sliding toward an excellent tribological performance

Novel two-dimensional (2D) Nb2C nanosheets were successfully prepared through a simple lultrasonic and magnetic stirring treatment from the original accordion-like powder. To further study their water-lubrication properties and deal with common oxidation problems, Nb2C nanosheets with different oxidation degrees were prepared and achieved long-term stability in deionized water. Scanning electron microscope (SEM), transmission electron microscope (TEM), scanning probe microscope (SPM), X-ray powder diffraction (XRD), Raman, and X-ray photoelectron spectrometer (XPS) experiments were utilized to characterize the structure, morphology, and dispersion of Nb2C nanosheets with different degrees of oxidation. The tribological behaviors of Nb2C with different degrees of oxidation as additives for water lubrication were characterized using a UMT-3 friction testing machine. The wear scars formed on the 316 steel surface were measured using three-dimensional (3D) laser scanning confocal microscopy. The tribological results showed that a moderately oxidized Nb2C nanosheet, which owned the composition of Nb2C/Nb2O5/C, displayed excellent tribological performance, with the friction coefficient (COF) decreasing by 90.3% and a decrease in the wear rate by 73.1% compared with pure water. Combining the TEM and Raman spectra, it was shown that Nb2O5 nanoparticles filled in the worn zone, and the layered Nb2C and C were adsorbed into the surface of the friction pair to form a protective lubricating film. This combined action resulted in an excellent lubricating performance.

Exploring cooperative porosity in organic cage crystals using in situ diffraction and molecular simulations.

A porous organic cage crystal, α-CC2, shows unexpected adsorption of sulphur hexafluoride (SF6) in its cage cavities: analysis of the static crystal structure indicates that SF6 is occluded, as even the smallest diatomic gas, H2, is larger than the window of the cage pore. Herein, we use in situ powder X-ray diffraction (PXRD) experiments to provide unequivocal evidence for the presence of SF6 inside the 'occluded' cage voids, pointing to a mechanism of dynamic flexibility of the system. By combining PXRD results with molecular dynamics simulations, we build a molecular level picture of the cooperative porosity in α-CC2 that facilitates the passage of SF6 into the cage voids.

Computationally Directed Discovery of MoBi2.

Incorporating bismuth, the heaviest element stable to radioactive decay, into new materials enables the creation of emergent properties such as permanent magnetism, superconductivity, and nontrivial topology. Understanding the factors that drive Bi reactivity is critical for the realization of these properties. Using pressure as a tunable synthetic vector, we can access unexplored regions of phase space to foster reactivity between elements that do not react under ambient conditions. Furthermore, combining computational and experimental methods for materials discovery at high-pressures provides broader insight into the thermodynamic landscape than can be achieved through experiment alone, informing our understanding of the dominant chemical factors governing structure formation. Herein, we report our combined computational and experimental exploration of the Mo-Bi system, for which no binary intermetallic structures were previously known. Using the ab initio random structure searching (AIRSS) approach, we identified multiple synthetic targets between 0-50 GPa. High-pressure in situ powder X-ray diffraction experiments performed in diamond anvil cells confirmed that Mo-Bi mixtures exhibit rich chemistry upon the application of pressure, including experimental realization of the computationally predicted CuAl2-type MoBi2 structure at 35.8(5) GPa. Electronic structure and phonon dispersion calculations on MoBi2 revealed a correlation between valence electron count and bonding in high-pressure transition metal-Bi structures as well as identified two dynamically stable ambient pressure polymorphs. Our study demonstrates the power of the combined computational-experimental approach in capturing high-pressure reactivity for efficient materials discovery.