Laboratory X-ray Diffraction Data Research Articles

Accurate crystal structure of ice VI from X-ray diffraction with Hirshfeld atom refinement.

Water is an essential chemical compound for living organisms, and twenty of its different crystal solid forms (ices) are known. Still, there are many fundamental problems with these structures such as establishing the correct positions and thermal motions of hydrogen atoms. The list of ice structures is not yet complete as DFT calculations have suggested the existence of additional and - to date - unknown phases. In many ice structures, neither neutron diffraction nor DFT calculations nor X-ray diffraction methods can easily solve the problem of hydrogen atom disorder or accurately determine their anisotropic displacement parameters (ADPs). Here, accurate crystal structures of H2O, D2O and mixed (50%H2O/50%D2O) ice VI obtained by Hirshfeld atom refinement (HAR) of high-pressure single-crystal synchrotron and laboratory X-ray diffraction data are presented. It was possible to obtain O-H/D bond lengths and ADPs for disordered hydrogen atoms which are in good agreement with the corresponding single-crystal neutron diffraction data. These results show that HAR combined with X-ray diffraction can compete with neutron diffraction in detailed studies of polymorphic forms of ice and crystals of other hydrogen-rich compounds. As neutron diffraction is relatively expensive, requires larger crystals which can be difficult to obtain and access to neutron facilities is restricted, cheaper and more accessible X-ray measurements combined with HAR can facilitate the verification of the existing ice polymorphs and the quest for new ones.

Investigating pair distribution function use in analysis of nanocrystalline hydroxyapatite and carbonate-substituted hydroxyapatite.

Hydroxyapatite (HA) is a complex material, which is often nanocrystalline when found within a biological setting. This work has directly compared the structural characteristics derived from data collected using a conventional laboratory-based X-ray diffractometer with those collected from a dedicated pair distribution function (PDF) beamline at Diamond Light Source. In particular, the application of PDF analysis methods to carbonated HA is evaluated. 20 synthetic samples were measured using both X-ray diffraction (XRD) and PDFs. Both Rietveld refinement (of laboratory XRD data) and real-space refinement (of PDF data) were used to analyse all samples. The results of Rietveld and real-space refinements were compared to evaluate their application to crystalline and nanocrystalline hydroxyapatite. Significant relationships were observed between real-space refinement parameters and increasing carbonate substitution. Understanding the local order of synthetic hydroxyapatite can benefit several fields, including both biomedical and clinical settings.

Ammonium Metatungstate, (NH4)6[H2W12O40]: Crystallization and Thermal Behavior of Various Hydrous Species

Various hydrous ammonium metatungstate phases (NH4)6[H2W12O40]·XH2O (AMT-X) have been obtained in the form of single crystals, using supersaturated solutions, antisolvent crystallization, and partial dehydration as strategies for crystal growth. On the basis of laboratory X-ray diffraction data, the crystal structures of the hydrous phases with X = 22, 12.5, 9.5, 8.5, 6, 4, and 2 as well of the cocrystals with X = 12-ethanol and X = 4-2acetone have been determined for the first time. AMT-22 forms the solid solution series (NH4)6–xKx[H2W12O40]·22H2O with the potassium salt (PMT-22) without a miscibility gap. Its tetragonal crystal structure shows a distorted cubic close-packed arrangement of the spherical α-Keggin-type [H2W12O40]6– anions with disordered ammonium N and water O atoms in the voids. The crystal structures of the other, less-hydrated AMT phases can be derived from distorted hexagonal rod packings of the α-Keggin anions, likewise with the cations and crystal water molecules in the voids. The thermal behavior of AMT-22 crystals reveals a quick dehydration, with AMT-9.5 as an intermediate and AMT-4 as a stable hydrate phase under ambient conditions. Upon further heating, the material decomposes with stepwise formation of AMT-2, AMT-1, AMT-0, and an amorphous phase, before orthorhombic WO3 forms above 400 °C. One of the commercially available AMT phases, “(NH4)6[H2W12O40]·XH2O” (with X = unspecified) has a water content of X = 4 but crystallizes in a structure other than AMT-4. Consequently, the 4-hydrate shows polymorphic behavior.

Local Structure and Influence of Sb Substitution on the Structure-Transport Properties in AgBiSe2.

Owing to their intrinsically low thermal conductivity and chemical diversity, materials within the I-V-VI2 family, and especially AgBiSe2, have recently attracted interest as promising thermoelectric materials. However, further investigations are needed in order to develop a more fundamental understanding of the origin of the low thermal conductivity in AgBiSe2, to evaluate possible stereochemical activity of the 6s2 lone pair of Bi3+, and to further elaborate on chemical design approaches for influencing the occurring phase transitions. In this work, a combination of temperature-dependent X-ray diffraction, Rietveld refinements of laboratory X-ray diffraction data, and pair distribution function analyses of synchrotron X-ray diffraction data is used to tackle the influence of Sb substitution within AgBi1-xSbxSe2 (0 ⩽ x ⩽ 0.15) on the phase transitions, local distortions, and off-centering of the structure. This work shows that, similar to other lone-pair-containing materials, local off-centering and distortions can be found in AgBiSe2. Furthermore, electronic and thermal transport measurements, in combination with the modeling of point-defect scattering, highlight the importance of structural characterizations toward understanding changes induced by elemental substitutions. This work provides new insights into the structure-transport correlations of the thermoelectric AgBiSe2.

Structures of 2 new sulfates, Na2M(SO4)2(M=Co, Ni), with rare SO42-coordination

In this study the structures of two new sulfates, Na2M(SO4)2(M=Co, Ni), were determined via both single crystal diffraction and neutron and laboratory X-ray diffraction data. The structural analysis was initiated with single crystal diffraction of the cobalt analogue and while this elucidated the cation positions the oxygen positions were still elusive. Therefore, combined Rietveld refinements of laboratory and neutron powder diffraction data was performed employing both hard constraints and soft restraints. The 5 K neutron data of both compounds are isostructural with the room temperature data as shown by Rietveld refinements. Refinements show that the transition metal ions are in a pseudo octahedral coordination that is better represented by a trigonal bipyramid, where one of the ligands is an edge of a SO42-tetrahedra. This rare coordination of sulfate tetrahedra was corroborated by spectroscopic techniques: UV-vis, Raman, and infrared. Additionally these compounds adopt large unit cells within the space group C2/c: Na2Co(SO4)2vol=4137.17(1)Å3and Na2Ni(SO4)2vol=4080.17(5) Å3.

Direct refinement of the atomic structure of MoS2layered compounds from PXRD

The graphene analog MoS2can be exfoliated into single-layer dispersion of MoS2crystals by reduction of starting material to LiMoS2followed by detachment of its layers in aqueous solvents. This dispersion reacts with organic salts in solution, producing precipitates of layered MoS2intercalated with their cations [1]. Most of these compounds have distinct chemical composition and powder X-ray diffraction (PXRD) patterns. The analysis of published data, however, indicates that these diffraction patterns were used only for fingerprinting and estimation of cation size and orientation by checking the positions of the basal (00l) reflections. The low-intensity hkl zone of the diffraction patterns was effectively ignored. In the current work, we report that the diffraction patterns of MoS2intercalation compounds contain enough information to refine their atomic structure directly. We found that the patterns of (NR4)x MoS2(R=alkyl, H) compounds correspond to turbostratic disorder of MoS2-organic layers. The patterns were indexed with a common orthorhombic cell. The cell content was Rietveld refined using a modification of a "supercell approach" [2,3] developed for full-pattern modeling of disordered clays. We determined that the Mo atoms in MoS2layers in the intercalation compounds change the coordination from prismatic to octahedral and that the S atoms form "nanorunnels" containing organic cations. The geometry of the Mo-Mo chains forming in the layer was consistent with the EXAFS data. The ordering of the organic layer depended on the nature of the cation, with (NEt4)x MoS2notably ordered enough to have specific stoichiometric composition (x=1/6) defined by the intralayer packing. The PW-DFT-d calculations based on our model confirmed our results. The developed approach allows determination of previously inaccessible atomic structures of a wide class of MoS2-based layered compounds using commercially available software and laboratory X-ray diffraction data.

Crystal Structural Study of Ho-doped Ceria Using X-ray Powder Diffraction Data

Crystal structural analysis of Ho-doped ceria (Ce0.7Ho0.3O1.85) was performed using both conventional laboratory and synchrotron X-ray diffraction (XRD) data. In the laboratory XRD data, a poor refinement result was achieved based on a cubic phase (space group Fm-3 m, No.225); weighted (Rwp) and profile (Rp) R-factors were 16.2 and 13.4 %, respectively. However, the R-factors significantly decreased to 8.76 and 6.87 % for the Rwp and Rp values, respectively, when a secondary cubic phase was added in the refinement model. While the phases were indistinguishable in the laboratory XRD data because of close peak positions, they were clearly separated in the synchrotron XRD data owing to monochromatic wavelength. The final Rietveld refinement results revealed that Ce0.7Ho0.3O1.85 consists of two cubic (Fm-3 m) phases; major Ce-rich phase (Ce:Ho = 78:22, with a lattice parameter of 5.4097(1) A) and minor Ho-rich phase (Ce:Ho = 45:55, with a lattice parameter of 5.3877(1) A). The ratio between the major and minor phases was 66:34. The final converged Rwp and Rp obtained from the synchrotron XRD data were 12.9 and 10.8 %, respectively.

Quantitative analysis of turbostratically disordered nontronite with a supercell model calibrated by the PONKCS method

Two calibration-based quantitative X-ray diffraction (XRD) models for turbostratically disordered Bulong nontronite, the PONKCS (partial or no known crystal structure) approach and the supercell structural model, were compared in terms of the accuracy and refinement error from Rietveld quantitative phase analysis. The PONKCS approach achieved improved nontronite quantitative results with synchrotron diffraction patterns compared with those achieved with laboratory XRD data as a result of better data quality and the use of Debye–Scherrer geometry with significantly reduced preferred orientation effects. The introduction of a peak shape modifier (spherical harmonics) to correct the quantification result is mainly useful for laboratory XRD patterns containing nontronite collected from Bragg–Brentano geometry with appreciable preferred orientation effects. A novel calibration approach for the nontronite supercell model was developed, based on the Rietveld quantitative formula in theTOPASsymbolic computation system. The calibrated supercell model achieved better accuracy (deviation within 1 wt%) and lower refinement error than the PONKCS approach because the physically based description of turbostratic disorder requires fewer refinable parameters than the PONKCS approach. The drawbacks and limitations of the supercell approach are also discussed.

Synthesis, Crystal Structure, and Microstructure Analysis of Perovskite-Type Compounds LnCo0.95Ni0.05O3 (Ln = La, Pr, Nd, Sm, Gd, and Dy)

The crystal structure and the microstructure of LnCo0.95Ni0.05O3 compounds, synthesized by a soft chemistry process, were studied. Synchrotron and laboratory X-ray diffraction data of LnCo0.95Ni0.05O3 (Ln = Pr, Nd, Sm, Gd, and Dy) can be refined in the Pbnm space group (SG). The orthorhombic symmetry has been confirmed by transmission electron microscopy. The X-ray diffraction data of LaCo0.95Ni0.05O3 can be fitted with rhombohedral Rc and monoclinic I2/a SG. The comparison of experimental electron diffraction with theoretical simulation showed the monoclinic symmetry for the La compound has a better match than that of the rhombohedral symmetry. The Pr compound has shown to have a three-dimensional microdomain texture in which the orientation of the real unit cell, i.e., approximately radical2ap x radical2ap x 2ap (where ap is the lattice parameter of the aristotype Pm3m perovskite, noted with a "p" subscript), alternates in each domain in one of the three space directions.

High-Pressure Synthesis and Properties of Solid Solutions between BiMnO3 and BiScO3

Solid solutions BiMn1-xScxO3 (0 ≤ x ≤ 1) were prepared at 6 GPa and 1383−1443 K. Selected area and convergent beam electron diffraction showed that BiMn0.9Sc0.1O3 crystallizes in the centrosymmetric space group C2/c at room temperature. The structure parameters of BiMn0.9Sc0.1O3 were refined by the Rietveld method from laboratory X-ray diffraction data (Z = 8; a = 9.6029(3) A, b = 5.60988(14) A, c = 9.7690(3) A, β = 108.775(2°) at 293 K). The Mn−O bond lengths suggest that the orbital order present in BiMnO3 at 300 K disappears in BiMn0.9Sc0.1O3. Therefore, the monoclinic-to-monoclinic phase transition observed in BiMnO3 at 474 K and associated with the orbital melting was not detected in BiMn1-xScxO3 for x ≥ 0.05 down to 133 K. BiMn1-xScxO3 were characterized by dc and ac magnetization, specific heat, and differential scanning calorimetry measurements. The long-range ferromagnetic order seems to survive for x = 0−0.2. For x ≥ 0.4, the samples showed spin-glass-like features. The Weiss temperature deduced...

D030 Structure determination from powder diffraction data of some moisture-sensitive, network coordination compounds

A series of new com pounds was discovered during the study of a novel solid lithium- ion battery electrolyte system based on succinonitrile. The phases LiX(succinonitrile)2 (X = PF6 - , AsF6 - , ClO4 - ) were identified as undesirable phases that formed at low salt concentrations in succinonitrile. The silver analogues of these systems also exist as crystalline phases, but the lithium salts do not share the same structure. The crystal structures of the Li salts were solved from laboratory X-ray diffraction data. The AsF6 - and PF6 - adducts are isostructural, with the monoclinic space group, P2. The ClO4 - adduct has a doubled unit cell volume compared to the AsF6 - and PF6 - materials and has the orthorhombic space group Pba2. The lithium coordination in these adducts helps explain why plastic crystal electrolytes using LiPF6 and LiClO4 salts have poor ionic conductivity at room temperature.

The crystal structure of the interrupted framework silicate K 9.6Ca 1.2Si 12O 30 determined from laboratory X-ray diffraction data

The crystal structure of a potassium calcium silicate with composition K 9.6Ca 1.2Si 12O 30 (or K 8CaSi 10O 25) has been solved by direct methods aided by distance least squares optimization from laboratory X-ray powder diffraction data. The trigonal compound adopts the non-centrosymmetric space group R 3 c with the following basic crystallographic data: a=11.13623(5) Å, c=21.9890(2) Å, V=2361.63(2) Å 3, Z=3, D calc=2.617 g cm −3. The crystal structure can be classified as an interrupted framework with exclusively Q 3-units. It can be thought of as being built from layers parallel to (001) containing isolated six-membered tetrahedral rings in UDUDUD conformation. Corner sharing of tetrahedra belonging to adjacent sheets results in a tetrahedral framework. The framework density of the structure is 15.2 T-atoms/1000 Å 3. The coordination sequences are identical for both silicon atoms in the asymmetric unit: 3-6-11-20-32-46-60-80-102-122. The vertex symbols for the two tetrahedral centers are 10 2·10 2·6 1. Topologically, the structure can be described as an Archimedean three-dimensional 3-connected net. It can be derived from the diamond or cristobalite net by removing 20% of the knots. Charge compensation in the structure is achieved by the incorporation of mono- and divalent M-cations ( M: K, Ca). These extra-framework ions are coordinated by six to nine oxygen ligands. Ca/K distributions for the five symmetrically independent M-sites were obtained from a combination of bond distance considerations, site occupancy refinements and the bulk chemical composition. The structural characterization is completed by a detailed Raman spectroscopic study. Furthermore, possible implications of the structural chemistry of interrupted framework silicates for the field of silicate glass research are addressed.

In1.06Ho0.94Ge2O7: A Thortveitite‐Type Compound.

AbstractFor Abstract see ChemInform Abstract in Full Text.

In1.06Ho0.94Ge2O7: a thortveitite-type compound.

A new indium holmium digermanate, In(1.06)Ho(0.94)Ge(2)O(7), with a thortveitite-type structure, has been prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system (space group C2/c, No. 15). The structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. The In(3+) and Ho(3+) cations occupy the same octahedral site, forming a hexagonal arrangement on the ab plane. In their turn, the hexagonal arrangements of (In/Ho)O(6) octahedral layers are held together by sheets of isolated diortho groups comprised of double tetrahedra sharing a common vertex. In this compound, the Ge(2)O(7) diortho groups lose the ideal D(3d) point symmetry and also the C(2h) point symmetry present in the thortveitite diortho groups. The Ge-O-Ge angle bridging the diortho groups is 160.2 (3) degrees, compared with 180.0 degrees for Si-O-Si in thortveitite (Sc(2)Si(2)O(7)). The characteristic mirror plane in the thortveitite space group (C2/m, No. 12) is not present in this new thortveitite-type compound and the diortho groups lose the C(2h) point symmetry, reducing to C(2).

Synthesis, crystal structure, and preliminary study of luminescent properties of InTbGe 2O 7

A new indium terbium germanate InTbGe 2O 7, which is a member of the thortveitite family, was prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system, space group C2/ c (No. 15), with unit cell parameters a=6.8818(2) Å, b=8.8774(3) Å, c=9.7892(4) Å, β=101.401(1)°, V=586.25(4) Å 3 and Z=4. Its structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. It consists of octahedral sheets that are held together by sheets of isolated Ge 2O 7 diorthogroups composed of two tetrahedra sharing a common vertex. It contains only one octahedral site occupied by In 3+ and Tb +3 cations. The characteristic mirror plane in the thortveitite (Sc 2Si 2O 7) space group ( C2/ m, No. 12) is not present in this new compound. Besides, in InTbGe 2O 7, the Ge–O–Ge angle bridging two diorthogroups is 156.8(2)° as compared to the one in thortveitite, which is 180°. On the other hand, luminescent properties were observed when it is excited with 376.5 nm wavelength. The luminescence spectrum shows typical transitions from the 5D 4 multiplet belonging to the trivalent terbium ion.

Structure of Zr2ON2 by Neutron Powder Diffraction: The Absence of Nitride–Oxide Ordering

The structure of the fluorite-related zirconium oxynitride Zr2ON2 has been refined against a combination of laboratory X-ray and time of flight neutron powder diffraction data. The structure is of the bixbyite (C-M2O3) type. The high symmetry of the powder diffraction pattern does not allow us to easily distinguish between fully ordered, fully disordered, or partially ordered anion models. However, Rietveld refinements against both high and medium resolution neutron powder diffraction data clearly favour a statistical distribution of oxide and nitride anions over a single crystallographic site which is contrary to the predictions of previous calculations. The space group is Ia3 (No. 206), with a=10.13940(7) Å at 298 K and Z= 16. This symmetry and unit cell are retained at low temperatures (a=10.1250(1) Å at 4.5 K). Partial oxidation reveals the existence of a phase with N2 molecules weakly bound and the stoichiometry ZrO2(N2)0.028(1). We also report the isostructural hafnium oxynitride Hf2ON2 (Ia3 with a=10.0692(2) Å at 298 K as determined using laboratory X-ray diffraction data).