Combined Synchrotron X-ray Diffraction Research Articles

KCaNb2O6F from a combined synchrotron X-ray and neutron powder diffraction study

Potassium calcium diniobium hexa­oxide fluoride, KCaNb2O6F, crystallizes in the cubic pyrochlore-type structure. In the crystal structure, NbO6 octa­hedra are linked together by common corners to form a three-dimensional [Nb2O6]2− network. (K,Ca) and F atoms, which are located in the voids of the [Nb2O6]2− network, form zigzag [(K,Ca)F]2+ chains. The K and Ca atoms are distributed statistically over the same crystallographic position (site-occupancy factor = 0.5), having an eightfold coordination by six O atoms from the NbO6 octa­hedra and by two F atoms. All atoms lie on special positions, viz. Nb has \overline{3}m, the (K,Ca) site has \overline{3}m, O has 2mm and F has \overline{4}3m site symmetry.

On the formation of voids in internal tin Nb3Sn superconductors

The formation of voids during the reaction heat treatment of internal tin Nb3Sn strands degrades the physical superconductor properties. The authors describe three void growth mechanisms on the basis of combined synchrotron microtomography and x-ray diffraction results obtained during in situ heating cycles. Initially, void growth is driven by a reduction of void surface area. The main void volume increase is caused by density changes during the formation of Cu3Sn in the strand. Long duration temperature ramps and isothermal holding steps neither reduce the void volume nor improve the chemical strand homogeneity prior to the superconducting A15 phase nucleation and growth.

Cooperative deformation of mineral and collagen in bone at the nanoscale

In biomineralized tissues such as bone, the recurring structural motif at the supramolecular level is an anisotropic stiff inorganic component reinforcing the soft organic matrix. The high toughness and defect tolerance of natural biomineralized composites is believed to arise from these nanometer scale structural motifs. Specifically, load transfer in bone has been proposed to occur by a transfer of tensile strains between the stiff inorganic (mineral apatite) particles via shearing in the intervening soft organic (collagen) layers. This raises the question as to how and to what extent do the mineral particles and fibrils deform concurrently in response to tissue deformation. Here we show that both mineral nanoparticles and the enclosing mineralized fibril deform initially elastically, but to different degrees. Using in situ tensile testing with combined high brilliance synchrotron X-ray diffraction and scattering on the same sample, we show that tissue, fibrils, and mineral particles take up successively lower levels of strain, in a ratio of 12:5:2. The maximum strain seen in mineral nanoparticles (approximately 0.15-0.20%) can reach up to twice the fracture strain calculated for bulk apatite. The results are consistent with a staggered model of load transfer in bone matrix, exemplifying the hierarchical nature of bone deformation. We believe this process results in a mechanism of fibril-matrix decoupling for protecting the brittle mineral phase in bone, while effectively redistributing the strain energy within the bone tissue.

Pressure-Induced Chemical Decomposition and Structural Changes of Boric Acid

A combined synchrotron X-ray diffraction, Raman scattering, and infrared spectroscopy study of the pressure-induced changes in H(3)BO(3) to 10 GPa revealed a new high-pressure phase transition between 1 and 2 GPa followed by chemical decomposition into cubic HBO(2), ice-VI, and ice- VII at approximately 2GPa. The layered triclinic structure of H(3)BO(3) exhibits a highly anisotropic compression with maximum compression along the c direction, accompanied by a strong reduction of the interlayer spacing. The large volume variation and structural changes accompanying the decomposition suggest high activation energy. This yields a slow reaction kinetics at room temperature and a phase composition that is highly dependent on the specific pressure-time path followed by the sample. The combined results have been used to propose a mechanism for pressure-induced dehydration of H(3)BO(3) that implies a proton disorder in the system.

Structural and magnetic properties of the Kagomé antiferromagnet YbBaCo 4O 7

The mixed-valent compound YbBaCo 4O 7 is built up of Kagomé sheets of CoO 4 tetrahedra, linked in the third dimension by a triangular layer of CoO 4 tetrahedra in an analogous fashion to that found in the known geometrically frustrated magnets such as pyrochlores and SrCr 9 x Ga 12−9 x O 19 (SCGO). We have undertaken a study of the structural and magnetic properties of this compound using combined high-resolution powder neutron and synchrotron X-ray diffraction. YbBaCo 4O 7 undergoes a first-order trigonal→orthorhombic phase transition at 175 K. We show that this transition occurs as a response to a markedly underbonded Ba 2+ site in the high-temperature phase and does not appear to involve charge ordering of Co 2+/Co 3+ ions in the tetrahedra. The symmetry lowering relieves the geometric frustration of the structure, and a long-range-ordered 3-D antiferromagnetic state develops below 80 K.

Structure and Magnetism in the Kagome Antiferromagnet RBaCo4O7

AbstractThe mixed-valent compound RBaCo4O7 (R=Rare earth, Y), hereafter abbreviated as R-114, is built up of Kagomé sheets of CoO4 tetrahedra, linked in the third dimension by a triangular layer of CoO4 tetrahedra in an analogous fashion to that found in the known geometrically frustrated magnets such as pyrochlores and SrCr9xGa12-9xO19 (SCGO). We have undertaken a study of the structural and magnetic properties of the Y-114 and Yb-114 compound using combined high resolution powder neutron and synchrotron X-ray diffraction. Both compounds undergo a first order trigonal → orthorhombic phase transition that breaks the trigonal symmetry of the structure. We show from Bond Valence Sum arguments that this transition occurs as a response to a markedly underbonded Ba2+ site in the high-temperature phase. The symmetry-lowering transition relieves the geometric frustration of the structure, and a long-range ordered 3-D antiferromagnetic state develops at low temperature. The magnetic structure of the Y compound has been solved and shows a compromise between the well-known 120° structure of the Kagomé net and a collinear antiferromagnet in the third dimension

Crystal Structure of Stoichiometric YBa2Fe3O8.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Combined synchrotron x-ray diffraction and micro-Raman for following in situ the growth of solution-deposited YBa2Cu3O7 thin films

A unique combination of in situ synchrotron x-ray diffraction and in situ micro-Raman spectroscopy was used to study the growth process of YBa2Cu3O6+x films obtained by metal organic decomposition using trifluoroacetate precursor on LaAlO3 substrates. The techniques give complementary information: x-ray diffraction gives insight into the structural growth, whereas micro-Raman spectroscopy gives information of the chemical composition with additional information on the texture. To perform both experiments in situ, a special high-temperature process chamber was designed.

Determination of elastic constants of a fiber-textured gold film by combining synchrotron x-ray diffraction and in situ tensile testing

The elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in situ tensile tester in a four-circle goniometer on a synchrotron beam line (LURE facility, France). The mechanical description of the substrate-thin film composite structure has been developed to determine the stress tensor in the film while the strong {111} fiber texture was taken into account using the crystallite group method (CGM). CGM strain analysis allowed us to forecast the nonlinear relationship between strain and sin2Ψ obtained for the thin films due to the strong anisotropy of gold. A least-square method was used to fit the overall experimental data with good accuracy and allows determining all single-crystal elastic constants.

Crystal Structure of Stoichiometric YBa2Fe3O8

The oxygen-nonstoichiometry locus in YBa2Fe3O(8+w) changes with the sign of w. The singularity at w = 0 is studied by Rietveld refinement of combined high-resolution, high-intensity neutron and synchrotron X-ray diffraction data collected at room temperature on red-colored stoichiometric YBa2Fe3O8. A residual disorder of oxygen atoms is identified in a concentration of 0.03 vacancy/interstitials per formula, with corresponding anisotropy in thermal displacements of oxygen neighbors. The disorder improves accommodation of trivalent iron over the two unequal coordination polyhedra and is not identical with the charged Frenkel disorder induced thermally. The symmetry of the cooperative magnetic order is Ib'am, with opposite moments of equal magnitude (4.07 micro(B) at 295 K) at the two iron sites.

Combined synchrotron x-ray diffraction and wafer curvature measurements during Ni–Si reactive film formation

Combined x-ray diffraction and wafer curvature measurements during annealing of Ni thin films (13 nm) deposited on Si (001) reveal distinct stages in stress development and silicide growth. Thanks to this unique experimental setup, a clear correlation is established between force extrema at distinct temperatures and the appearance of new silicides. It is shown that the transient formation of Ni3Si2 has a strong influence on the overall stress development.

Determination of the Crystal Structure of Mg(AlH4)2 by Combined X‐Ray and Neutron Diffraction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Elastic behavior of fibre-textured gold films by combining synchrotron X-ray diffraction and in-situ tensile testing

AbstractThe elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in-situ tensile tester in a four-circle goniometer at a synchrotron beam line (LURE facility, France). Knowing the stress tensor in the film, the strong {111} fibre texture was taken into account using the Crystallite Group Method (CGM). CGM strain analysis allows predicting a non linear relationship between strain and sin2 Ψ obtained for the thin films due to the strong anisotropy of gold. In contrast, the average of strains in longitudinal and transversal directions varies linearly with sin2 Ψ. The evolution of the slope of these curves as a function of the applied stresses in the film allowed determining the single-crystal elastic constant s44 of thin gold films.

Determination of the crystal structure of Mg(AlH 4) 2 by combined X-ray and neutron diffraction

The structure of magnesium alanate, Mg(AlH 4) 2, has been examined in detail by combined powder synchrotron X-ray and neutron diffraction. The space group is confirmed to be P 3 ¯ m 1 with unit cell dimensions of a = 5.2084(3) Å and c = 5.8392(5) Å at 8 K, a = 5.20309(12) Å and c = 5.8400(2) Å at 111 K and a = 5.1949(2) Å and c = 5.8537(2) Å at 295 K. The structure consists of isolated and slightly distorted AlH 4 − tetrahedra that are connected via six-coordinated Mg atoms in a distorted octahedral geometry, resulting in a sheet-like structure along the crystallographic c-axis. The distortion of the AlH 4 − tetrahedra decreases with increasing temperature, whereas, the opposite is the case for the MgH 6 octahedra. The Al–H distances are 1.606(10)–1.634(4) Å, 1.602(10)–1.682(3) Å and 1.561(12)–1.672(4) Å at 8, 111 and 295 K, respectively.

Atomic ordering in the doped rare earth cobaltates Ln0.33Sr 0.67CoO 3− δ ( Ln=Y 3+, Ho 3+ and Dy 3+)

The perovskite-based rare earth cobaltates ( Ln 0.33Sr 0.67CoO 3− δ ) ( Ln=Y 3+, Ho 3+ and Dy 3+) have been synthesized at 1100°C under 1 atm oxygen. A thermogravimetric study has determined the overall oxygen content in each case while a combined electron diffraction (ED) and synchrotron X-ray diffraction study has revealed the presence of a complex, previously unreported, perovskite-related superstructure phase. ED gave a resultant C1 c1 but most probably Cmcm ( a =2a p −2c p , b =4b p , c =2a p +2c p ) perovskite-related superstructure, describable as a modulated I4/ mmm intermediate parent structure. Synchrotron X-ray data has been used to refine the intermediate parent structures of all three compounds. Coupled Ln/Sr and O/vacancy ordering and associated structural relaxation is shown to be responsible for the observed superstructure.

The Structure of Li3AlD6.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The structure of Li 3AlD 6

The structure of Li 3AlD 6 has been determined by combined synchrotron X-ray and neutron diffraction. The space group is R 3 with unit-cell dimensions a=8.07117(10) and c=9.5130(2) Å. The structure consists of isolated and close to regular AlD 6 3− octahedra, which are connected via six-coordinated Li. The Al–D distances are 1.734–1.754 Å, and the Li–D distances are 1.892–2.120 Å. The shortest D–D distance of 2.395 Å is found within the octahedra. The structure can be described as a distorted bcc structure of AlD 6 3− units with all tetrahedral sites filled with Li.

Crystal Structure Data for Efavirenz (Sustiva™) by Combined Synchrotron X-Ray Diffraction and Electron Microscopy Techniques

Efavirenz (Sustiva™) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) for the treatment of HrV-infected patients and has been in the market since 1998. Efavirenz exists as three different polymorphs (Forms I, II, III) and a nonstochiometric heptane solvate (Form IV). The current synthetic process for Efavirenz yields Form IV which is converted to the desired Form I polymorph by heating. One of the concerns for any drug substance is whether a consistent crystal form is produced in order to insure consistent physical and chemical properties, as well as to safeguard pharmacokinetic profiles. The sensitivity and resolution of single-crystal x-ray diffraction, the traditional method employed to determine unit cell parameters of drug compounds in development, are limited for Efavirenz Form IV because of the small crystallite size of the material. Furthermore, Efavirenz Form IV materials, depending on the process conditions, have slightly different powder diffraction patterns in terms of intensity when collected on standard in-house diffractometers.

Effects of temperature and composition on the bulk modulus of (Mg,Fe)O

Isothermal static compression data for MgO at 300 and 1100 K were obtained by combining synchrotron X-ray diffraction techniques with an externally heated high-temperature diamond-anvil cell that is capable of achieving pressures greater than 125 GPa at temperatures up to 1100 K. The experiments at 300 K were conducted under both hydrostatic and nonhydrostatic conditions. The deviatoric stress in non-hydrostatic environment significantly effects the measured lattice parameters. Fits to the static compression data of MgO at 300 K yield a bulk modulus of 185(7) GPa and 160(2) GPa under nonhydrostatic and hydrostatic conditions, respectively. The deviatoric stress decreases with increasing temperature, and a nearly hydrostatic condition was achieved at temperatures above 900 K when NaCl was used as a pressure-medium. The bulk modulus of MgO was determined to be 135(3) GPa at a temperature of 1100 K, yielding its temperature derivative of 20.030(3) GPa/K. Comparing these results with previous studies in the system MgO-FeO, shows that the bulk modulus of (Mg,Fe)O decreases with increasing FeO content, from 160 GPa for MgO to 146 GPa for FeO.

Synthesis and Structure of Hg 1−x Cr x Sr 2 CuO 4+δ Mercurocuprates

We report preliminary results concerning the synthesis and structural characterisation of the chromium stabilised 1201 phases: Hg1−xCrxSr2CuO4+δ. A systematic study of the formation of phases in this system has been undertaken, together with a combined powder neutron and synchrotron x-ray diffraction study, to address the issue of chromium clustering and ordering in this system.