Synchrotron X-ray Powder Diffraction Study Research Articles

Lanthanide distribution in some doped alkaline earth aluminates and gallates

High-resolution neutron and synchrotron X-ray powder diffraction studies are reported for the six oxides AB 2O 4 ( A=Ca 2+, Sr 2+ and Ba 2+ and B=Al 3+ and Ga 3+). These oxides all adopt a stuffed tridymite type structure, the precise nature of which depends on both the A- and B-type cations. Bond valence calculations reveal a range of values for the various A-type cations, in all cases at least one site is significantly underbonded. Conversely the tetrahedral B-type sites invariably exhibit unexceptional bond valencies. Attempts to dope the oxides with various lanthanides to the 1% level invariably resulted in some segregation into alternate phases located at the grain boundaries. The identity of the impurity phases is presented and the importance of bond valencies in understanding this segregation is highlighted.

Co- and Ni-exchanged ferrierite: The contribution of synchrotron X-ray diffraction data to siting of TMIs

High-silica zeolites exchanged with transition metal ions (TMIs) are the subject of great interest for their unusual catalytic activity and selectivity. Structural information like coordination and accessibility of TMIs in zeolites are important factors for understanding their catalytic activity. Siting of TMIs in zeolites is typically obtained by spectroscopic (EXAFS, EPR, UV–vis and IR) and computational methods, as in the case of Co-ferrierite. However, some controversy exists in the literature concerning the model for incorporation of bare Co ions in ferrierite. We show here that the results of our synchrotron X-ray powder diffraction studies on Co- and Ni-exchanged ferrierite (Si/Al = 8.5) are in a good agreement with the model of Co siting based on an indirect spectroscopic approach and help to validate this model. By direct structural evidences, a possible explanation for the larger catalytic activity of Co sites in the main channels of ferrierite can be inferred. A combination of data from in situ XRD continuous monitoring of the Co ion migration during calcination and crystal-chemical considerations allows to device a strategy for the design of optimised co-cations containing Co-ferrierite catalysts.

High pressure synchrotron x-ray powder diffraction study ofSc2Mo3O12 and Al2W3O12

Synchrotron x-ray powder diffraction was used to studySc2Mo3O12 and Al2W3O12 at high pressure in a DAC. Both compounds adopt the orthorhombicSc2W3O12 structure under ambient conditions and exhibit anisotropicnegative thermal expansion. A phase transition from orthorhombic(Pnca) to monoclinic(P 21/a) symmetrywas observed at ∼0.25 GPa for Sc2Mo3O12 andat ∼0.1 GPa forAl2W3O12 associated with avolume reduction of ∼1.5–2%. A second crystalline to crystalline phase transition was clearly seen only forSc2Mo3O12 (2.5–3.0 GPa). Peak broadening and almost complete amorphization were observed forSc2Mo3O12 at∼8 GPa, and this was not fully reversible on decompression. At 7 GPa, the amorphization ofAl2W3O12 was not as advanced as for the molybdate and on decompressioncrystalline material was recovered. The compressibility of orthorhombicSc2Mo3O12 is highly anisotropic, but it is almost isotropic for both monoclinicSc2Mo3O12 and Al2W3O12. Both compounds show a reduction in their bulk moduli(K0) atthe orthorhombic to monoclinic transition: 32(2) GPa for orthorhombic and 16(1) GPa for monoclinicSc2Mo3O12, and 48 GPa for orthorhombic and 28(1) GPa for monoclinicAl2W3O12.Sc2Mo3O12 displays very similar high pressure behaviour to the previously studiedSc2W3O12.

Synchrotron X-ray powder diffraction studies on the order–disorder phase transition in lithium ferrites

Investigations on the manganese substituted lithium ferrites reveal the strong influence of manganese ions on the ordering of Li + cations in the spinel-type crystal lattice. We present the effect of Mn 3+ substitution in the LiFe 5− x Mn x O 8 (0 ≤ x ≤ 1) samples on the order–disorder phase transition and on the thermal expansion of their spinel lattices. Synchrotron X-ray measurements have been performed in the temperature range 10–300 K and 300–1173 K. The diffraction experiments were carried out at the DESY-HASYLAB high-resolution powder diffractometer (beamline B2). The transition from ordered (cubic primitive, P4 1 32) to disordered (face centred cubic, Fd3m) structure was observed with the increasing Mn 3+ content.

High Temperature Structural Studies of Ba2BiTaO6.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synchrotron X-ray powder diffraction study of hexagonal turkey egg-white lysozyme

The structure of turkey egg-white lysozyme (TEWL) has been refined from high-resolution X-ray powder diffraction data. The sample was rapidly obtained as a polycrystalline precipitate at high protein concentration using 0.5 M NaCl solvent pH 6 and was deposited in the PDB with code 1xft. The diffraction data were collected at room temperature. Molecular replacement was shown to give a suitable starting point for refinement, illustrating that powder data can be sufficient for this approach. Crystallographic models were then refined by combined Rietveld and stereochemical restraint analysis of the powder data (d(min) = 3.35 A), resulting in the extraction of reliable lattice parameters and the refinement of the molecular conformation at room temperature. The structure is hexagonal [space group P6(1)22, unit-cell parameters a = 71.0862 (3), c = 85.0276 (5) A] with 12 symmetry-related molecules in the unit cell, in agreement with previous studies. The results of our analysis are indicative of specific amino acids being disordered at this temperature. Upon cooling, a sudden drop in the lattice parameters at approximately 250 K is observed concurrently with the freezing of the mother liquor. The observation of severe peak broadening below this temperature indicates strain effects accompanying the freezing transition, which are found to be reversible. Finally, a correlation between the unit-cell parameters and the pH of the buffer solution is evident, in a similar manner to earlier observations on HEWL.

Erratum: Synchrotron x-ray powder diffraction study of the structural phase transition inCaBr2[Phys. Rev. B70, 144102 (2004)

Erratum: Synchrotron x-ray powder diffraction study of the structural phase transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>CaBr</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>[Phys. Rev. B<b>70</b>, 144102 (2004)

High temperature structural studies of Ba 2BiTaO 6

Synchrotron X-ray powder diffraction studies have shown that the Bi and Ta are ordered on the B-sites of the double perovskite Ba 2BiTaO 6. At room temperature the structure is rhombohedral R 3 ¯ and this transforms to a cubic structure F m 3 ¯ m near 250 °C. The R 3 ¯ to F m 3 ¯ m transition appears to be continuous. Although the temperature dependence of both the rhombohedral angle and volume strain show anomalous behavior, both are indicative of a second order phase transition.

Synchrotron x-ray powder diffraction study of the structural phase transition inCaBr2

The structures of $\mathrm{Ca}{\mathrm{Br}}_{2}$ have been investigated using high resolution synchrotron powder x-ray diffraction methods between room temperature and $800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. At room temperature $\mathrm{Ca}{\mathrm{Br}}_{2}$ has an orthorhombic $\mathrm{Ca}{\mathrm{Cl}}_{2}$-type structure $(Pnnm\phantom{\rule{0.3em}{0ex}}\mathrm{Z}=2)$ with $a=6.8847(1)$, $b=6.5806(1)$, and $c=4.3477(1)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Heating above $560\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ results in a continuous transition to a tetragonal rutile type structure $(P{4}_{2}∕mnm\phantom{\rule{0.3em}{0ex}}\mathrm{Z}=2)$ with $a=6.810\phantom{\rule{0.2em}{0ex}}95(7)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ and $c=4.417\phantom{\rule{0.2em}{0ex}}70(5)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ at $650\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Investigation, through either spontaneous strain or octahedral tilt angle, suggests that the transition is close to second order in nature, although the contribution from the sixth order term in the Landau potential cannot be neglected.

High temperature structure of BaBiO 3—a synchrotron X-ray powder diffraction study

The structure of the valence ordered perovskite-like compound BaBiO 3 has been studied at fine temperature intervals between room temperature and 923 K using high resolution synchrotron X-ray powder diffraction methods. The compound undergoes two structural phase transitions, a first order transition to a rhombohedral structure near 425 K and a second-order transition to a cubic structure, the transition temperature being estimated as 893 K.

Synchrotron X-ray powder diffraction studies on the phase transitions in LiMn 2O 4

Structural phase transitions of the spinel lithium-manganese oxide, LiMn 2O 4 ( Fd3m at room temperature) in the temperature range of 300–20 K, were investigated using synchrotron and laboratory X-ray powder diffraction. Splitting of the spinel X-ray lines 311, 400, 440, 531, 533 and 622, recorded during the test, evidenced the reversible formation of cubic, orthorhombic and tetragonal structures. The first transformation starts at ∼290 K as a cubic ( Fd3m)→orthorhombic ( Fddd) symmetry reduction, and both phases coexist down to 260 K. Below 100 K a second structural transition, orthorhombic→tetragonal ( F4 1 /ddm) was observed, with the coexistence of these two phases down to ∼40 K. The supercell corresponding to 3 a×3 a× a ( a, spinel unit-cell constant) has been considered for both orthorhombic and tetragonal polymorphs of LiMn 2O 4, based on the appearance of (2.10.0) superstructure X-ray reflection.

Neutron and temperature-resolved synchrotron X-ray powder diffraction study of akaganéite

Rietveld refinements using neutron powder diffraction data were used to locate H atom positions and obtain a more precise crystal structure refinement for akaganéite [Fe 3+ 7.6 Ni 2+ 0.4 O 6.35 (OH) 9.65 Cl 1.25 ·nH 2 O]. Difference Fourier maps clearly showed H atoms positions near those O atoms at the midpoints of the tunnel edges. The O-H vectors point toward the Cl sites at the center of the tunnel, and weak hydrogen bonds likely form between the framework O atoms and Cl. The Cl position is near the center of a prism defined by the eight hydroxyl H atoms. The Cl atoms fill ~2/3 of the tunnel sites, suggesting an ordering scheme in a given tunnel with every third tunnel site vacant. Such an arrangement allows the Cl anions to increase their separation distance along a tunnel by displacing away from one another toward their respective adjacent vacancies. The Fe-O octahedra in akaganéite are distorted with Fe-(O, OH) distances ranging from 1.94 to 2.13 Å and show three longer and three shorter Fe-O distances; as expected the longer distances are associated with the OH- anions. Temperature-resolved synchrotron X-ray powder diffraction data and Rietveld refinements were used to investigate changes in the akaganéite structure and its transformation into hematite as it was heated from 26 to 800 °C. Rietveld refinements revealed surprising consistency in all unit-cell parameters between room temperature and ~225 °C, resulting in nearly zero thermal expansion of the akaganéite structure over a 200 °C interval. Above ~225 °C, the unit-cell volume gradually decreased, primarily in response to decreases in c and b, and an increase in the b angle. The a parameter remained nearly constant until ~225 °C and increased thereafter. Akaganéite started to transform to hematite in the temperature range 290 to 310 °C with no evidence for maghemite as an intermediate phase.

Single crystal growth of transition metal oxides at high pressures of several GPa

Single crystals of various transition metal oxides exhibiting fascinating physical properties were grown by flux method at high pressures of several GPa. The growth conditions were determined based on synchrotron powder X-ray diffraction studies at high-pressure and high-temperature conditions. Results on a S=1/2 one dimensional alternating exchange antiferromagnet (VO) 2P 2O 7, perovskites PrNiO 3, CaFeO 3, BiMnO 3 and an oxychloride high- T C superconductor Ca 2− x Na x CuO 2Cl 2 are reported.

高圧合成法を用いた新しい遷移金属酸化物の探索と単結晶育成

High pressure synthesis is a powerful technique in searching for new materials. Generally speaking, however, it used to be almost impossible to obtain single crystal samples of these high-pressure phases. To be reported here is the single crystal growths of various transition metal oxides by means of flux method based on the synchrotron X-ray powder diffraction studies at high pressures of several GPa. Some results on the structure analysis based on synchrotron X-ray powder diffraction will also be shown.

Synthetic MgAl2O4(spinel) at high-pressure conditions (0.0001–30 GPa): A synchrotron X-ray powder diffraction study

The equation of state and the structural behavior of synthetic MgAl2O4 have been investigated using synchrotron X-ray powder diffraction data collected to 30 GPa at room temperature. The Birch-Murnaghan, Vinet, and Poirier-Tarantola models have been fitted to the observed P-V data. The Birch-Murnaghan equation of state, with V fixed at its experimental value, yields K = 190.8(±1.2) GPa, K ′ = 6.77(±0.15) and K ″ = −0.075 GPa−1 (implied value). The compression of spinel occurs with a negligible change of the fractional coordinate of oxygen. Therefore the structural shrinking is a function of cell edge shortening alone. The results presented here are compared with those from the literature.

Single crystal growth of Ca2-xNaxCuO2Cl2 and related compounds at high pressures of several GPa

Single crystal samples of the oxychloride superconductor Ca 2-x Na x CuO 2 Cl 2 were obtained by flux method at high pressures of several GPa. The growth conditions were determined based on synchrotron powder X-ray diffraction studies at high pressure and high temperature conditions as in the case of (VO) 2 P 2 O 7 high pressure phase.

The equation of state of PbTiO3 up to 37 GPa: a synchrotron x-ray powderdiffraction study

High-pressure synchrotron x-ray powder diffraction patterns were collected usingID09 of ESRF (Grenoble, France) for a powder sample of PbTiO3, placed in adiamond anvil cell. The patterns were collected at room temperature usingnitrogen (up to 37 GPa) and methanol–ethanol solution (up to 7 GPa) aspressure-transmitting media. The bulk moduli were calculated for the first timeusing the Vinet equation of state and they were compared to those of isostructuralcompounds. The trend of the spontaneous polarization as a function of pressureconfirms that the ferroelectric–paraelectric phase transition at 11.2 GPa possessesa second-order character.

Temperature dependent synchrotron X-ray powder diffraction studies: Fe(II) spin crossover complexes

Temperature dependent synchrotron X-ray powder diffraction studies: Fe(II) spin crossover complexes

Synchrotron X-ray powder diffraction study on successive phase transitions inAZnPO4(A:Rb, Cs)

Synchrotron X-ray powder diffraction study on successive phase transitions in<i>A</i>ZnPO₄(<i>A</i>:Rb, Cs)

Synchrotron X-ray and TOF neutron powder diffraction study of a lyonsite-type oxide Co3.6Fe3.6(VO4)6

Co 3.6 Fe 3.6 (VO 4 ) 6 was synthesized by solid-state reaction at 900 °C, and its structure was determined by X-ray and neutron powder diffraction. Co 3.6 Fe 3.6 (VO 4 ) 6 is isotypic with lyonsite (space group: Pnma; Z =2), having lattice parameters of a =4.96480(9) Å, b =10.2245(2) Å, and c =17.2100(3) Å. Its structure parameters were refined by the Rietveld method with two sets of synchrotron X-ray (wavelengths: 0.85001 and 1.74500 Å) and time-of-flight neutron powder diffraction data. Co 2+ and Fe 3+ ions are distributed among three different metal sites M 1– M 3. Not Co 2+ ions but Fe 3+ ions are mainly contained in face-sharing M 3O 6 octahedra, forming single chains parallel to the [1 0 0] direction. Edge- and corner-sharing octahedra M 2O 6 build up layers perpendicular to the [0 0 1] direction. Edge-sharing trigonal prisms M 1O 6 form zig-zag single chains along the [1 0 0] direction. The M 1 and M 3 sites are about 6.0(2)% and 34.0(2)% deficient, respectively. The tendency for Co 2+ and Fe 3+ ions to distribute among the three metal sites is discussed on the basis of the electrostatic valence rule. Graphic