X-ray Powder Diffraction Experiments Research Articles

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.

In situ probing of the thermal treatment of h-BN towards exfoliation

Two-dimensional (2D) hexagonal boron nitride (h-BN) is becoming increasingly interesting for wider engineering applications. Thermal exfoliation is being suggested as a facile technology to produce large quantities of 2D h-BN. Further optimization of the process requires fundamental understanding of the exfoliation mechanism, which is hardly realized by ex situ techniques. In this study, in situ synchrotron x-ray powder diffraction experiments are conducted while heat treating bulk h-BN up to 1273 K. During the heating process, linear expansion of c-axis is observed and the contraction of a-axis up to around 750 K is consistent with previous research. However, a changing behavior from contraction to expansion in a-axis direction is newly observed when heating over 750 K. With the consideration of previous thermally oxidation studies, a hypothesis of thermal assisted exfoliation with oxygen interstitial and substitution of nitrogen at high temperature is proposed.

Secondary Metal Coordination Using a Tetranuclear Complex as Ligand Leading to Hexanuclear Complexes with Enhanced Thermal Barriers for Electron Transfer

Postsynthesis of the paramagnetic square-shaped complex {[(Tp*Me)Fe(μ-CN)2(CN)][Co(dmbpy)2]}2(BPh4)2·6MeCN·H2O [1, Tp*Me = tris(3,4,5-trimethylpyrazole)-borate; dmbpy = 4,4′-dimethyl-2,2′-bipyridin...

Structural and physical properties of trilayer nickelates R4Ni3O10 ( R=La , Pr, and Nd)

We investigate the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, high-resolution synchrotron powder X-ray diffraction and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry, and undergo a metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At MMT, the lattice parameters show distinct anomalies; however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen in magnetic and thermal measurements, which suggest a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with experiments. We show that the 9-fold coordinated Pr ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering at 5 K. The Pr ions located in the perovskite block (PB) layers with 12-fold coordination, however, exhibit a non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like anomaly near35 K, and an upturn below T = 10 K suggesting the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy fermion behavior could be found in any of the three compounds.

Crystal structure and phase transition of TlReO4: a combined experimental and theoretical study

The present work describes a density-functional theory (DFT) study of TlReO4 in combination with powder x-ray diffraction experiments as a function of temperature and Raman measurements at ambient temperature. X-ray diffraction measurements reveal three different structures as a function of temperature. A monoclinic structure (space group P21/c) is observed at room temperature while two isostructural tetragonal structures (space group I41/a) are found at low- and high-temperature. In order to complement the experimental results first-principles DFT calculations were performed to compute the structural energy differences. From the total energies it is evident that the monoclinic structure has the lowest total energy when compared to the orthorhombic structure, which was originally proposed to be the structure at room temperature, which agrees with our experiments. The structural and vibrational properties of the low- and room-temperature phase of TlReO4 have been calculated using DFT. Inclusion of van der Waals correction to the standard DFT exchange correlation functional is found to improve the agreement with the observed structural and vibrational properties. The Born effective charge of these phases has also been studied which shows a combination of ionic and covalent nature, resembling metavalent bonding. Calculations of zone-center phonon frequencies lead to the symmetry assignment of previously reported low-temperature Raman modes. We have determined the frequencies of the eight infrared-active, 13 Raman-active and three silent modes of low-temperature TlReO4 along with 105 infrared-active and 108 Raman-active modes for room-temperature TlReO4. Phonons of these two phases of TlReO4 are mainly divided into three regions which are below 150 cm−1 due to vibration of whole crystal, 250 to 400 cm−1 due to wagging, scissoring, rocking and twisting and above 900 cm−1 due to stretching in ReO4 tetrahedron. The strongest infrared peak is associated to the internal asymmetric stretching of ReO4 whereas the strongest Raman peak is associated to the internal symmetric stretching of ReO4. We have also measured the room-temperature Raman spectra of monoclinic TlReO4 identifying up to 28 modes. This Raman spectrum has been interpreted by comparison with the previously reported Raman frequencies of the low-temperature phase and our calculated Raman frequencies of low- and room-temperature phases of TlReO4.

Significant recycled efficiency of multifunctional nickel molybdenum oxide nanorods in photo-catalysis, electrochemical glucose sensing and asymmetric supercapacitors

In this paper, we report significant recycled efficiency of nickel molybdenum oxide (NMO) nanorods for multi-functional catalytic activities in photo-catalysis, electrochemical glucose sensing and asymmetric supercapacitors. Initially, we have used NMO nanorods as the photo-catalysts for organic dye degradation reactions using visible light source. The NMO nanorods show momentous photocatalytic activity in degradation of organic dye (~90% in 160 min) and also exhibit excellent regeneration efficiency. Consequently, the photo-catalysts were recovered via batch experiments for further use in other applications including electrochemical glucose sensing and asymmetric supercapacitors. Powder X-ray diffraction (XRD) and electron microscopic experiments were conducted before and after photo-catalysis for the materials stability. The recovered NMO nanorods show significant electrochemical detection of glucose in 0.1 M KOH. Moreover, the recovered NMO nanorods show promising nature for supercapacitors. The specific capacitance of recovered NMO nanorods was found to be ~660 F/g at 2 mV/s in 5 M KOH. Charge-discharge and stability of the electrodes were also studied for the commercial purpose.