High-resolution X-ray Powder Research Articles

Solid solution formation in the metatorbernite-metazeunerite system (Cu(UO2)2(PO4)2- x(AsO4) x. nH2O) and their stability under conditions of variable temperature.

Mineral phases which can be thought of as members of a metatorbernite-metazeunerite solid solution (Cu(UO2)2(PO4)2- x(AsO4) x.8H2O have been identified in radioactive samples from spoil heaps at the uranium mine site in South Terras, Cornwall (grid reference SW935523). A complete solid solution (0 < x < 2) was synthesized by precipitation from solution using uranium (VI) nitrate and copper (II) chloride and phosphoric acid/arsenic acid in the appropriate molar proportions. Refined unit cell parameters determined by Pawley fitting of powder X-ray diffraction data showed a linear variation in the a unit cell parameter according to Vegard's Law, allowing the composition of the natural mineral phases found at South Terras to be determined from measurement of their unit cell parameters. High-resolution variable-temperature synchrotron powder X-ray diffraction studies were carried out at the Diamond Light Source on three members of this solid solution ( x = 0, 1, 2) and showed different structural behaviour as a function of composition and temperature. Metatorbenite ( x = 0) retains its tetragonal symmetry at low temperatures and dehydrates to an amorphous phase at 473 K, whereas metazeunrite ( x = 2) transforms to an orthorhombic phase at low temperatures, regains its tetragonal symmetry on heating to 323 K and undergoes a further transition to an, as yet, unidentified phase at 473 K. This article is part of the theme issue 'Fifty years of synchrotron science: achievements and opportunities'.

Uniaxial Expansion of the 2D Ruddlesden-Popper Perovskite Family for Improved Environmental Stability.

The unique hybrid nature of 2D Ruddlesden-Popper (R-P) perovskites has bestowed upon them not only tunability of their electronic properties but also high-performance electronic devices with improved environmental stability as compared to their 3D analogs. However, there is limited information about their inherent heat, light, and air stability and how different parameters such as the inorganic layer number and length of organic spacer molecule affect stability. To gain deeper understanding on the matter we have expanded the family of 2D R-P perovskites, by utilizing pentylamine (PA)2(MA) n-1Pb nI3 n+1 ( n = 1-5, PA = CH3(CH2)4NH3+, C5) and hexylamine (HA)2(MA) n-1Pb nI3 n+1 ( n = 1-4, HA = CH3(CH2)5NH3+, C6) as the organic spacer molecules between the inorganic slabs, creating two new series of layered materials, for up to n = 5 and 4 layers, respectively. The resulting compounds were extensively characterized through a combination of physical and spectroscopic methods, including single crystal X-ray analysis. High resolution powder X-ray diffraction studies using synchrotron radiation shed light for the first time to the phase transitions of the higher layer 2D R-P perovskites. The increase in the length of the organic spacer molecules did not affect their optical properties; however, it has a pronounced effect on the air, heat, and light stability of the fabricated thin films. An extensive study of heat, light, and air stability with and without encapsulation revealed that specific compounds can be air stable (relative humidity (RH) = 20-80% ± 5%) for more than 450 days, while heat and light stability in air can be exponentially increased by encapsulating the corresponding films. Evaluation of the out-of-plane mechanical properties of the corresponding materials showed that their soft and flexible nature can be compared to current commercially available polymer substrates (e.g., PMMA), rendering them suitable for fabricating flexible and wearable electronic devices.

Mild Hydrothermal Crystallization of Heavy Rare-Earth Chromite RECrO3 (RE = Er, Tm, Yb, Lu) Perovskites and Magnetic Properties.

Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especially true for the small metal cations at the A-site with large distortion angle of CrO6 octahedral and small Goldschmidt tolerance factors. Here, we performed a progressive dehydration crystallization strategy to synthesize four RECrO3 with the smallest radii of rare earth elements (Er, Tm, Yb, Lu) in mild hydrothermal conditions. Profile refinement of the high-resolution powder X-ray diffraction results indicated slightly longer unit cell parameters of a and c in our samples with a higher distorted angle of CrO6 octahedral units along ⟨010⟩ direction. All of the samples show rounded rectangle plate morphology with uniform distribution of particle sizes. These four RECrO3 crystals can only form in a very narrow mineralization temperature range, i.e., 260-280 °C and 4.45-6.24 M of KOH. HRTEM results indicated that the normal crystallographic direction is ⟨001⟩, and the lattice of steps at the edge of elliptic rounded crystal is consistent with the bulk, which demonstrated single crystalline nature of the as-obtained crystals. Room-temperature Raman and FT-IR spectra reveal a continuous symmetry mode shift-dependent on the radii of A-site rare-earth cations. Temperature-dependent magnetization curves of RECrO3 show typical antiferromagnetism to paramagnetism transition with Néel temperature of 93, 90, 86, and 83 K for ErCrO3, TmCrO3, YbCrO3, and LuCrO3, respectively. Samples of YbCrO3 and LuCrO3 show clear magnetization reversal and exchange bias phenomena below their Néel points. This paper indicates that the coupling of magnetic exchange in perovskite structure oxides could be tailorable in mild hydrothermal condition, towards the exploration of new magnetic and other physical properties.

Evidence of continuous pottery production during the late Byzantine period in the Studenica Monastery, a UNESCO World Heritage Site

A collection of 63 pottery shards excavated at the Studenica Monastery, Serbia, originating from two distinct cultural strata (late 12th until the late 13th century, and the 14th and the first half of 15th century) was subject of this work. Mineralogical and chemical composition of body and glaze and production technology of investigated pottery were determined combining optical microscopy, inductively coupled plasma-optical emission and wavelength dispersive X-ray fluorescence spectrometry, Fourier transform infrared and micro-Raman spectroscopy, high-resolution synchrotron powder X-ray diffraction and multivariate statistical analysis. In addition, clay rod with traces of glaze from the kiln found within the Monastery complex was investigated. The firing temperature was estimated at 600–700 °C for the most of cookware and at 800–1000 °C for tableware. Pottery, made of non-calcareous clay, was covered with transparent lead based glaze and copper and iron were used as colorants. Combining results of all used techniques no significant differences in mineralogical and chemical composition among samples from two cultural strata were identified indicating continuous pottery production process from 13th until 15th century in Studenica.

Bulk properties of the van der Waals hard ferromagnet VI3

We present comprehensive measurements of the structural, magnetic and electronic properties of layered van-der-Waals ferromagnet VI$_3$ down to low temperatures. Despite belonging to a well studied family of transition metal trihalides, this material has received very little attention. We outline, from high-resolution powder x-ray diffraction measurements, a corrected room-temperature crystal structure to that previously proposed and uncover a structural transition at 79 K, also seen in the heat capacity. Magnetization measurements confirm VI$_3$ to be a hard ferromagnet (9.1 kOe coercive field at 2 K) with a high degree of anisotropy, and the pressure dependence of the magnetic properties provide evidence for the two-dimensional nature of the magnetic order. Optical and electrical transport measurements show this material to be an insulator with an optical band gap of 0.67 eV - the previous theoretical predictions of d-band metallicity then lead us to believe VI$_3$ to be a correlated Mott insulator. Our latest band structure calculations support this picture and show good agreement with the experimental data. We suggest VI$_3$ to host great potential in the thriving field of low-dimensional magnetism and functional materials, together with opportunities to study and make use of low-dimensional Mott physics.

Reactivity of Solid Rubrene with Potassium: Competition between Intercalation and Molecular Decomposition

We present the synthesis and characterization of the K+-intercalated rubrene (C42H28) phase, K2Rubrene (K2R), and identify the coexistence of amorphous and crystalline materials in samples where the crystalline component is phase-pure. We suggest this is characteristic of many intercalated alkali metal-polyaromatic hydrocarbon (PAH) systems, including those for which superconductivity has been claimed. The systematic investigation of K-rubrene solid-state reactions using both K and KH sources reveals a complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K2R, K(RR*), and K xR' (where R* and R' are rubrene decomposition derivatives C42H26 and C30H20, respectively). K2R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous byproducts from the decomposition of rubrene. K(RR*) is synthesized as a single phase, and K xR' is obtained only as a secondary phase to the majority K2R phase. The crystal structure of K2R was determined using high-resolution powder X-ray diffraction, revealing that the structural rearrangement from pristine rubrene creates two large voids per rubrene within the molecular layers in which K+ is incorporated. K+ cations accommodated within the large voids interact strongly with the neighboring rubrene via η6, η3, and η2 binding modes to the tetracene cores and the phenyl groups. This contrasts with other intercalated PAHs, where only a single void per PAH is created and the intercalated K+ weakly interacts with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-Cphenyl bonds. For the crystalline decomposition derivative products K(RR*) and K xR', a lack of definitive structural information with regard to R* and R' prevents the crystal structures from being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.

Combining a nine-crystal multi-analyser stage with a two-dimensional detector for high-resolution powder X-ray diffraction

The high-resolution powder diffraction beamline at ESRF (ID22), built with a dual-undulator source on the 6 GeV storage ring, combines a wide continuous range of incident energy (6–80 keV) with high brightness, offering the possibility to carry out high-flux high-resolution powder diffraction measurements. In routine operation, a bank of nine scintillation detectors is scanned vertically to measure the diffracted intensity versus 2θ, each detector being preceded by an Si 111 analyser crystal. Although the current detector system has operated successfully for the past 20 years, recent developments in detector technology could be exploited to improve the overall performance. With this in mind, as a test, a two-dimensional Pilatus3 X CdTe 300 K-W pixel detector has been mounted on the arm of the diffractometer, replacing the nine scintillator detectors. At each nominal 2θ value, a two-dimensional image is recorded showing nine distinct regions corresponding to the diffraction signals passing via each of the analyser crystals. This arrangement offers new flexibility in terms of data handling and processing, with the possibility to optimize both peak shape and statistics, to remove parasitic effects, and to gain spatial resolution information. Combining the high efficiency of a hybrid photon-counting area detector with the high angular resolution given by analyser crystals is an effective approach to improving the overall performance of high-resolution powder diffraction.

Position and oxidation state of tin in Sn-bearing tetrahedrites Cu12-xSnxSb4S13

We have explored the homogeneity range of Cu12-xSnxSb4S13 tetrahedrites, the peculiarities of their crystal structure, and the oxidation state of tin in them. Phase analysis and crystal structure refinement based on high-resolution powder X-ray diffraction have shown that tin-bearing tetrahedrites exist to the maximum of 0.75÷0.8 tin atoms per formula, with the cubic unit cell parameter increasing from 10.331 to 10.391 Å. The analysis of atomic parameters have proved that tin substitutes for copper only on the Cu(1) site, which is characterized by a regular tetrahedral coordination. The substitution site is further confirmed by 119Sn Mössbauer spectroscopy, showing the low quadrupole splitting, Δ = 0.14–0.16 mm s−1, evidencing the highly-symmetric tetrahedral coordination of tin. Also, the +4 oxidation state of tin directly follows from the isomer shifts values, δ = 1.50–1.52 mm s−1.

Crystal Chemistry of Three Volcanic K-rich Nepheline Samples From Oldoinyo Lengai, Tanzania and Mount Nyiragongo, Eastern Congo, Africa

Natural nepheline (Nph) samples are intermediate members of solid solutions that extend from the pure Na end-member Na[AlSiO4] to the pure K end-member K[AlSiO4] (= kalsilite, Kls). We examined two volcanic nepheline (ideally, K2Na6[Al8Si8O32] or Nph0.75Kls0.25) samples from Oldoinyo Lengai, Tanzania (samples 1 and 2) and a third sample 3 from Mount Nyiragongo, Eastern Congo. The crystal structure of these three samples was obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements in space group P63. Satellite reflections were not observed in these samples. The EPMA composition of sample 1 is {K1.50Na0.19Ca0.070.23}Σ2(Na)6[Si8.35Al7.48Fe0.18]Σ16.00O32. The A site contains 0.23 vacancies () with some Na and Ca atoms, whereas the B site is completely filled with only Na atoms. From the EPMA formula, K(sof) = 0.844 and Na(sof) = 1.0. The refinement unit-cell parameters are a = 10.00247(1), c = 8.38396(1) A, V = 726.431(1) A3; K(sof) = 0.779(2) and Na(sof) = 0.988(2). The composition of sample 2 is {K1.670.33}Σ2(Na5.76K0.174Ca0.06)Σ6[Si8.44Al7.37Fe0.20]Σ16.01O32, so K(sof) = 0.835 and Na(sof) = 1.030. Sample 2 has a = 10.01769(2), c = 8.39586(2) A, V = 729.678(1) A3, K(sof) = 0.812(2), and Na(sof) = 0.995(2). Sample 3 is a three-phase (3a, 3b, 3c) intergrowth with an average formula of {K1.770.23}2(Na4.30K1.51Ca0.19)Σ6[Si8.13Al7.76Fe0.11]Σ16.00O32, K(sof) = 0.887, and Na(sof) = 1.208. A large amount of K and Ca atoms occur in the B site. Based on the weight percentages and sofs of the three phases, the Rietveld refinement gives an average K(sof) = 0.859 and Na(sof) = 1.145. The average distances indicate a high degree of Al-Si disorder in samples 1, 2, and phase 3b. These African samples extend natural nepheline solid solutions to about Nph0.55Kls0.45. The average distance increases linearly with Na(sof) and V across nepheline solid solutions because K atoms enter the Na site. K-rich nepheline seems to always contain vacancies in the A site.

Nitro-functionalized Bis(pyrazolate) Metal-Organic Frameworks as Carbon Dioxide Capture Materials under Ambient Conditions.

The metal-organic frameworks (MOFs) M(BPZNO2 ) (M=Co, Cu, Zn; H2 BPZNO2 =3-nitro-4,4'-bipyrazole) were prepared through solvothermal routes and were fully investigated in the solid state. They showed good thermal stability both under a N2 atmosphere and in air, with decomposition temperatures peaking up to 663 K for Zn(BPZNO2 ). Their crystal structure is characterized by 3D networks with square (M=Co, Zn) or rhombic (M=Cu) channels decorated by polar NO2 groups. As revealed by N2 adsorption at 77 K, they are micro-mesoporous materials with BET specific surface areas ranging from 400 to 900 m2 g-1 . Remarkably, under the mild conditions of 298 K and 1.2 bar, Zn(BPZNO2 ) adsorbs 21.8 wt % CO2 (4.95 mmol g-1 ). It shows a Henry CO2 /N2 selectivity of 15 and an ideal adsorbed solution theory (IAST) selectivity of 12 at p=1 bar. As a CO2 adsorbent, this compound is the best-performing MOF to date among those bearing a nitro group as a unique chemical tag. High-resolution powder X-ray diffraction at 298 K and different CO2 loadings revealed, for the first time in a NO2 -functionalized MOF, the insurgence of primary host-guest interactions involving the C(3)-NO2 moiety of the framework and the oxygen atoms of carbon dioxide, as confirmed by Grand Canonical Monte Carlo simulations. This interaction mode is markedly different from that observed in NH2 -functionalized MOFs, for which the carbon atom of CO2 is involved.

(Invited) Electrochemical Methods for Surface Composition Determination of Alloy and Core/Shell Nanoparticles

The surface characteristics of metallic nanoparticles (NPs), especially the atomic percent and distribution of each component, is critical to their catalytic and electrocatalytic behavior. Therefore, efforts are underway to design NP catalysts with full control of their composition, both in the bulk and at the surface. In our work, Pt-Ru and Pt-Ir NPs, either in alloy or core@shell forms, are of great interest, due to their suitability for a wide range of electrocatalytic and sensing applications, such as for the oxidation of formic acid, alcohols, and ammonia, for oxygen evolution and reduction in regenerative fuel cells, in the reduction of hydrogen peroxide, and as an electron mediating matrix in glucose biosensors 1–8. In the present work, PtxIry alloys, Ircore@Ptshell, Rucore@Ptshell, and Rucore@Pt-Irshell NPs were synthesized using the simple and controllable polyol method 9. In the case of PtxIry alloy NPs, two sequential heating steps were employed to minimize the possibility of surface enrichment of Pt or Ir during NP formation. In the case of Ircore@Ptshell and Rucore@Ptshell NPs, the Ptshell, with a coverage of between 0.1 and 2 monolayers (MLs), was controllably deposited on the surface of the Ircore and Rucore NPs, while for the Rucore@Pt-Irshell NPs, one ML of the PtxIry alloy shell, containing different Pt:Ir ratios, was deposited on the Rucore. Wavelength dispersive X-ray spectroscopy (WDS) and energy dispersive X-ray spectroscopy, coupled with high-resolution transmission electron microscopy (EDS/HRTEM) and powder X-ray diffraction (PXRD), were then used to determine the bulk composition and homogeneity of the NPs. To determine the outer surface composition of these NPs, the underpotential deposition/stripping of Cu and oxalic acid oxidation have been used previously, e.g., for Pt-Ru NPs 10–12. However, the effect of NP size, Pt-Ru interactions at the surface, and the degree of Ru oxidation on the catalytic activity have not been determined. In other prior work 13, CO stripping was used to establish the stability of PtRu NPs by tracking the changes in the surface composition. In the present work, several electrochemical fingerprinting methods were developed (underpotential deposition/removal of H atoms, CO stripping, and surface oxide reduction) to determine the precise coverage and thickness (fraction of MLs) of the Ptshell on the Ircore@Ptshell and Rucore@Ptshell, NPs and the Pt:Ir ratio at the surface of the PtxIry alloy and Rucore/Pt-Irshell NPs, as well as the real surface area of the exposed metals. Figure 1 1,14,15 shows the CO stripping voltammetry of the NPs under study here as an example of how the peak potential and splitting correlate with the NP surface composition. A comparison will be given between the surface areas and compositions obtained by each of the electrochemical methods used here, as well as with what can be inferred from TEM imaging methods.

Benzoquinone-Bridged Heterocyclic Zwitterions as Building Blocks for Molecular Semiconductors and Metals.

In pursuit of closed-shell building blocks for single-component organic semiconductors and metals, we have prepared benzoquino-bis-1,2,3-thiaselenazole QS, a heterocyclic selenium-based zwitterion with a small gap (λmax = 729 nm) between its highest occupied and lowest unoccupied molecular orbitals. In the solid state, QS exists in two crystalline phases and one nanocrystalline phase. The structures of the crystalline phases (space groups R3 c and P21/ c) have been determined by high-resolution powder X-ray diffraction methods at ambient and elevated pressures (0-15 GPa), and their crystal packing patterns have been compared with that of the related all-sulfur zwitterion benzoquino-bis-1,2,3-dithiazole QT (space group Cmc21). Structural differences between the S- and Se-based materials are interpreted in terms of local intermolecular S/Se···N'/O' secondary bonding interactions, the strength of which varies with the nature of the chalcogen (S vs Se). While the perfectly two-dimensional "brick-wall" packing pattern associated with the Cmc21 phase of QT is not found for QS, all three phases of QS are nonetheless small band gap semiconductors, with σRT ranging from 10-5 S cm-1 for the P21/ c phase to 10-3 S cm-1 for the R3 c phase. The bandwidths of the valence and conduction bands increase with applied pressure, leading to an increase in conductivity and a decrease in thermal activation energy Eact. For the R3 c phase, band gap closure to yield an organic molecular metal with a σRT of ∼102 S cm-1 occurs at 6 GPa. Band gaps estimated from density functional theory band structure calculations on the ambient- and high-pressure crystal structures of QT and QS correlate well with those obtained experimentally.

Nonmonotonic particle-size-dependence of magnetoelectric coupling in strained nanosized particles of BiFeO3

Using high resolution powder x-ray and neutron diffraction experiments, we determined the off-centered displacement of the ions within a unit cell and magnetoelectric coupling in nanoscale BiFeO3 (≈20–200 nm). We found that both the off-centered displacement of the ions and magnetoelectric coupling exhibit nonmonotonic variation with particle size. They increase as the particle size reduces from bulk and reach maximum around 30 nm. With further decrease in particle size, they decrease precipitously. The magnetoelectric coupling is determined by the anomaly in off-centering of ions around the magnetic transition temperature (TN). The ions, in fact, exhibit large anomalous displacement around the TN which is analyzed using group theoretical approach. It underlies the nonmonotonic particle-size-dependence of off-centre displacement of ions and magnetoelectric coupling. The nonmonotonic variation of magnetoelectric coupling with particle size is further verified by direct electrical measurement of remanent ferroelectric hysteresis loops at room temperature under zero and ∼20 kOe magnetic field. Competition between enhanced lattice strain and compressive pressure appears to be causing the nonmonotonic particle-size-dependence of off-centre displacement while coupling between piezo and magnetostriction leads to nonmonotonicity in the variation of magnetoelectric coupling.

Interplay between Calcite, Amorphous Calcium Carbonate, and Intracrystalline Organics in Sea Urchin Skeletal Elements

Biomineralization processes in living organisms result in the formation of skeletal elements with complex ultrastructures. Although the formation pathways in sea urchin larvae are relatively well known, the interrelation between calcite, amorphous calcium carbonate (ACC), and intracrystalline organics in adult sea urchin biominerals is less clear. Here, we study this interplay in the spines and test plates of the Paracentrotus lividus sea urchins. Thermogravimetric analysis coupled with differential scanning calorimetry or mass spectrometry measurements, nuclear magnetic resonance technique, and high-resolution powder X-ray diffraction show that pristine spines and test plates are composed of Mg-rich calcite and comprise about 1.2 to 1.6 wt % organics, 10 wt % of anhydrous ACC and less than 0.2 wt % of water. Anhydrous ACC originates from incomplete crystallization of a precursor ACC phase during biomineralization and is associated with intracrystalline organics at the molecular level. Molecular interacti...

Evidence for negative thermal expansion in the superconducting precursor phase SmFeAsO

The fluorine-doped rare-earth iron oxypnictide series SmFeAsO1−xFx (0 0.10) was investigated with high resolution powder x-ray scattering. In agreement with previous studies (Margadonna et al 2009 Phys. Rev. B. 79 014503), the parent compound SmFeAsO exhibits a tetragonal-to-orthorhombic structural distortion at = 130 K which is rapidly suppressed by 0.10 deep within the superconducting dome. The change in unit cell symmetry is followed by a previously unreported magnetoelastic distortion at 120 K. The temperature dependence of the thermal expansion coefficient reveals a rich phase diagram for SmFeAsO: (i) a global minimum at 125 K corresponds to the opening of a spin-density wave instability as measured by pump-probe femtosecond spectroscopy (Mertelj et al 2010 Phys. Rev. B 81 224504) whilst (ii) a global maximum at 110 K corresponds to magnetic ordering of the Sm and Fe sublattices as measured by magnetic x-ray scattering (Nandi et al 2011 Phys. Rev. B 84 055419). At much lower temperatures than , SmFeAsO exhibits a significant negative thermal expansion on the order of −40 ppm · K−1 in contrast to the behaviour of other rare-earth oxypnictides such as PrFeAsO (Kimber et al 2008 Phys. Rev. B 78 140503) and the actinide oxypnictide NpFeAsO (Klimczuk et al 2012 Phys. Rev. B 85 174506) where the onset of 0 only appears in the vicinity of magnetic ordering. Correlating this feature with the temperature and doping dependence of the resistivity and the unit cell parameters, we interpret the negative thermal expansion as being indicative of the possible condensation of itinerant electrons accompanying the opening of a SDW gap, consistent with transport measurements (Tropeano et al 2009 Supercond. Sci. Technol. 22 034004).

Lead apatites: structural variations among Pb5(BO4)3Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite).

The crystal structure of four Pb apatite samples, Pb5(BO4)3Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space group P63/m and Z = 2. For this isotypic series, B = P5+ is pyromorphite, B = As5+ is mimetite and B = V5+ is vanadinite. The ionic radius for As5+ (0.355 Å) is similar to that of V5+ (0.335 Å), and this is twice as large as that for P5+ (0.170 Å). However, the c unit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes, V, are almost equal to each other. No explanation was available for this peculiar c-axis value for mimetite. Structural parameters such as average 〈B-O〉 [4], 〈Pb1-O9〉 [9] and 〈Pb2-O6Cl2〉 [8] distances increase linearly with V (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2-O1 distance, so the O1 oxygen atom interacts with the 6s2 lone-pair electrons of the Pb2+ cation that causes the Cl-Cl distance (= c/2) to increase to the largest value in the series because of repulsion, which causes the c-axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.

Synthesis, X-ray powder diffraction and DFT-D studies of indole-based compounds

Abstract Four indole-based compounds have been synthesized and their crystal structures determined using high-resolution synchrotron powder X-ray diffraction. In vacuo density function theory (DFT) optimization has been used in building initial molecular models for structure solution with the help of the Cambridge structure database. All four compounds were found to crystallize in the monoclinic space group P21/c. Dispersion-corrected DFT (DFT-D) has been used for experimental crystal structure validation with acceptable agreement found between the DFT-optimized and final refined structures. Three of the compounds exhibit bronchodilation properties with potency comparable to the theophylline (standard reference).

Ammonium fluoride mediated mechano chemical synthesis of A2PdF6 (A = K, Rb) along with their catalytic role in environmental remediation

To highlight the power of mechanochemistry to oxidize metal ions leading to the discovery of newer phases, ammonium fluoride mediated synthesis of A2PdF6 (A=Rb,K) has been carried out. Grinding reactions of ammonium fluoride with palladium (II) acetate and further cation exchange with AF (A=Rb,K) were closely monitored ex-situ characterizations such as high resolution powder X-ray diffraction (PXRD), fourier transform infrared (FT-IR) and Raman spectroscopy measurements. For the reaction involving RbF, Rb2PdF6 possessing K2PtCl6 type structure was confirmed from the Rietveld refinement of PXRD pattern, high resolution transmission emission microscopy (HR-TEM) and selected area electron diffraction (SAED) measurements. Elemental composition and oxidation state of palladium in Rb2PdF6 were examined using X-ray photoelectron spectroscopy (XPS) analysis. Ligand to metal charge transfer and d-d transitions of Pd (IV) were present in the UV–vis diffuse reflectance spectrum of Rb2PdF6 with a band gap of 2.67eV estimated using the Kubelka–Munk function. Its role as a catalyst to degrade the aqueous dye solutions (Methylene Blue, Malachite Green, Rhodamine-6G and Rhodamine-B) under UV–vis radiation has been evaluated along with their kinetics. The catalyst was active after four cycles of use. The reduction of Pd4+ to Pd0 by NaBH4 has been favourably used for the efficient and rapid conversion of highly carcinogenic, toxic, mutagenic Cr6+ to less toxic Cr3+. K2PdF6 possessing cubic K2PtCl6-type structure has also been synthesized for the first time by this method which presented yet another example for the alteration of reaction landscapes by mechanical forces.

Reaction Heterogeneity in LiNi0.8Co0.15Al0.05O2 Induced by Surface Layer

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact versus an eroded Li2CO3 surf...

Growth Oscillatory Zoning in Erythrite, Ideally Co3(AsO4)2·8H2O: Structural Variations in Vivianite-Group Minerals

The crystal structure of an oscillatory zoned erythrite sample from Aghbar mine, Bou Azzer, Morocco, was refined using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data, Rietveld refinement, space group C2/m, and Z = 2. The crystal contains two sets of oscillatory zones that appear to have developed during epitaxial growth. The unit-cell parameters obtained are a = 10.24799(3) Å, b = 13.42490(7) Å, c = 4.755885(8) Å, β = 105.1116(3)°, and V = 631.680(4) Å3. The empirical formula for erythrite, obtained with electron-probe micro-analysis (EPMA), is [Co2.78Zn0.11Ni0.07Fe0.04]∑3.00(AsO4)2·8H2O. Erythrite belongs to the vivianite-type structure that contains M1O2(H2O)4 octahedra and M22O6(H2O)4 octahedral dimers that are linked by TO4 (T5+ = As or P) tetrahedra to form complex layers parallel to the (010) plane. These layers are connected by hydrogen bonds. The average &lt;M1–O&gt;[6] = 2.122(1) Å and average &lt;M2–O&gt;[6] = 2.088(1) Å. With space group C2/m, there are two solid solutions: M3(AsO4)2·8H2O and M3(PO4)2·8H2O where M2+ = Mg, Fe, Co, Ni, or Zn. In these As- and P-series, using data from this study and from the literature, we find that their structural parameters evolve linearly with V and in a nearly parallel manner despite of the large difference in size between P5+ (0.170 Å) and As5+ (0.355 Å) cations. Average &lt;T–O&gt;[4], &lt;M1–O&gt;[6], and &lt;M2–O&gt;[6] distances increase linearly with V. The average &lt;As–O&gt; distance is affected by M atoms, whereas the average &lt;P–O&gt; distance is unaffected because it contains shorter and stronger P–O bonds. Although As- and P-series occur naturally, there is no structural reason why similar V-series vivianite-group minerals do not occur naturally or cannot be synthesized.