Single crystal X-ray studies of cation-deficient magnetite

1997 ◽  
Vol 212 (6) ◽  
Author(s):  
H. Okudera
Keyword(s):  
Single Crystal ◽  
Cation Vacancy ◽  
Site Preference ◽  
Mean Square ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cation Deficiency ◽  
Octahedral Cation ◽  
Synthetic Magnetite ◽  
Cation Sites

AbstractSite preference of cation vacancy and the effect of cation deficiency on the structure parameters have been investigated for synthetic magnetite specimens by means of the single-crystal X-ray diffraction methods. The cation vacancies are selectively formed at the octahedral cation sites even in the specimen quenched from 1793 K. The effects of cation deficiency are found as increase of atomic mean square displacements and decrease of anisotropy in thermal motions of the octahedral site cations.

Ternary aurides RE4Mg3Au10 (RE=Y, Nd, Sm, Gd–Dy) and their silver analogues

2015 ◽  
Vol 70 (2) ◽  
pp. 135-141 ◽  
Author(s):  
Theresa Block ◽  
Michael Johnscher ◽  
Stefan Linsinger ◽  
Ute Ch. Rodewald ◽  
Rainer Pöttgen
Keyword(s):  
Three Dimensional ◽  
Intermetallic Phases ◽  
Point Of View ◽  
Site Preference ◽  
Induction Melting ◽  
X Ray Diffraction ◽  
X Ray ◽  
Synthesis Conditions ◽  
Coordination Numbers ◽  
Cation Sites

AbstractThe ternary aurides RE4Mg3Au10 (RE=Y, Nd, Sm, Gd–Dy) and their silver analogues were synthesized by induction melting of the elements in sealed niobium tubes. These intermetallic phases were characterized by powder X-ray diffraction. They crystallize with the Ca4In3Au10-type structure, which, from a geometrical point of view, is a ternary ordered version of Zr7Ni10 with the rare earth and magnesium atoms ordering on the four crystallographically independent zirconium sites. The structures of crystals from three differently prepared gadolinium samples were refined from single-crystal X-ray diffractometer data: Cmca, a=1366.69(3), b=998.07(4), c=1005.54(3) pm, wR2=0.0332, 1234 F2 values, 46 variables for Gd4.43Mg2.57Au10, a=1378.7(1), b=1005.3(1), c=1011.2(1) pm, wR2=0.0409, 1255 F2 values, 48 variables for Gd5.50Mg1.50Au10, and a=1350.2(5), b=995.5(1), c=1009.3(1) pm, wR2=0.0478, 1075 F2 values, 48 variables for Gd5.61Mg1.39Au10. All crystals show substantial Mg/Gd mixing on two sites. The gold atoms form a pronounced two-dimensional substructure with Au–Au distances of 278 to 297 pm in Gd4.43Mg2.57Au10. These gold blocks are condensed via magnesium atoms (278–315 pm Mg–Au). The gadolinium atoms fill larger cavities within the three-dimensional networks. The magnesium vs. gadolinium site preference is a consequence of the different coordination numbers of the cation sites. All phases show homogeneity ranges RE4+xMg3–xAg10 and RE4+xMg3–xAu10. The influence of the synthesis conditions is briefly discussed.

scholarly journals The High Pressure Behavior of Galenobismutite, PbBi2S4: A Synchrotron Single Crystal X-ray Diffraction Study

Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 210 ◽  
Author(s):  
Paola Comodi ◽  
Azzurra Zucchini ◽  
Tonci Balić-Žunić ◽  
Michael Hanfland ◽  
Ines Collings
Keyword(s):  
High Pressure ◽  
Single Crystal ◽  
Structural Changes ◽  
Calcium Ferrite ◽  
X Ray Diffraction ◽  
Third Order ◽  
Electron Pairs ◽  
X Ray ◽  
Cation Sites ◽  
Murnaghan Equation

High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a FE-fE plot, yielding V0 = 697.4(8) Å3, K0 = 51(1) GPa and K’ = 5.0(2). The axial moduli were M0a = 115(7) GPa and Ma’ = 28(2) for the a axis, M0b = 162(3) GPa and Mb’ = 8(3) for the b axis, M0c = 142(8) GPa and Mc’ = 26(2) for the c axis, with refined values of a0, b0, c0 equal to 11.791(7) Å, 14.540(6) Å 4.076(3) Å, respectively, and a ratio equal to M0a:M0b:M0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.

scholarly journals Mean Square Vibration Amplitudes in Zinc

1977 ◽  
Vol 30 (1) ◽  
pp. 105 ◽  
Author(s):  
DW Field
Keyword(s):  
Single Crystal ◽  
Debye Temperature ◽  
Mean Square ◽  
X Ray Diffraction ◽  
Zinc Single Crystal ◽  
X Ray ◽  
Structure Factors ◽  
Principal Directions ◽  
The Mean ◽  
Integrated Intensities

The structure factors of 98 independent reflections have been determined by measurement of the integrated intensities for X-ray diffraction from a zinc single crystal at 295 K. The mean square vibration amplitudes found for the two principal directions are' compared with 'other recent measurements. The X-ray Debye temperature determined from the data' is 207 � 3 K at 295 K.

Rare Earth Site Preference in the Doped Laser Host Material Sc2SiO5. A Single-Crystal X-Ray Study

2012 ◽  
Vol 67 (2) ◽  
pp. 113-117 ◽  
Author(s):  
Ute Ch. Rodewald ◽  
Lihe Zheng ◽  
Birgit Heying ◽  
Xiaodong Xu ◽  
Liangbi Su ◽  
...  
Keyword(s):  
Rare Earth ◽  
Single Crystal ◽  
Diffraction Data ◽  
Host Material ◽  
Site Preference ◽  
Czochralski Technique ◽  
X Ray Diffraction ◽  
High Quality ◽  
X Ray ◽  
Oxygen Coordination

Single crystals of the laser host material Sc2SiO5 as well as thulium- (4 at.-%) and ytterbium- (5 at.-%) doped samples were prepared by the Czochralski technique. The structures of Sc2SiO5, Tm3+:Sc2SiO5, and Yb3+:Sc2SiO5 were refined on the basis of high-quality single-crystal X-ray diffraction data: monoclinic Y2SiO5 type, space group C2/c. The X-ray data unambiguously show that the larger rare earth cations exclusively occupy the 8 f site with oxygen coordination number 7.

Incommensurately modulated crystal structure of flamite – natural analogue of \alpha _{\rm H}^{\prime}-Ca2SiO4

2019 ◽  
Vol 75 (6) ◽  
pp. 1137-1143
Author(s):  
Sergey V. Rashchenko ◽  
Yurii V. Seryotkin ◽  
Ella V. Sokol ◽  
Svetlana N. Kokh
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Ambient Temperature ◽  
Single Crystal ◽  
Diffraction Data ◽  
Natural Analogue ◽  
X Ray Diffraction ◽  
X Ray ◽  
Incommensurate Modulation ◽  
Cation Sites

Crystal structures of unquenchable high-temperature polymorphs of Ca2SiO4, important in cement chemistry, have eluded single-crystal X-ray analysis. However, the problem may be addressed by studying chemically stabilized Ca2SiO4 polymorphs at ambient temperature. Here an incommensurately modulated crystal structure of flamite [Pnma(0β0)00s, q = 0.2728 (2)b*, a = 6.8588 (2) Å, b = 5.4301 (2) Å, c = 9.4052 (3) Å] is described. It is a mineral analogue of orthorhombic \alpha _{\rm H}^{\prime}-Ca2SiO4 (stable between 1160 and 1425°C), naturally stabilized by substitution with phosphorus. The incommensurate modulation results from wave-like displacement of cation sites accompanied by tilting of (Si,P)O4 tetrahedra and variation of the Na/(Ca + Na + K) ratio along the modulation period. The studied sample from Hatrurim Basin (Negev Desert, Israel) with composition (Ca1.75K0.12Na0.12)1.99(Si0.74P0.26)1.00O4 also demonstrates pseudomerohedral cyclic twinning around the a axis, which results from pseudohexagonal topology of the crystal structure and complicates the indexing of X-ray diffraction data.

Temperature dependence of structure parameters in natural magnetite: single crystal X-ray studies from 126 to 773 K

1996 ◽  
Vol 52 (3) ◽  
pp. 450-457 ◽  
Author(s):  
H. Okudera ◽  
K. Kihara ◽  
T. Matsumoto
Keyword(s):  
Single Crystal ◽  
Temperature Dependence ◽  
Temperature Rise ◽  
Structural Parameters ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
Increasing Temperature ◽  
Cation Sites

Structural parameters and their thermal changes in natural magnetite, Fe3O4, have been studied using the single-crystal X-ray diffraction method in the temperature range 126–773 K. The cell dimensions, oxygen coordinate and atomic mean square displacements (m.s.d.'s) reversibly change as a function of temperature. The coordinate of oxygen remains almost constant at x = 0.2549 (1) below ~600 K, but increases with increasing temperature above this temperature. This characteristic behavior of the oxygen coordinate with temperature indicates that the cation disordering over the tetrahedral (A) and octahedral (B) cation sites occurs above 600 K. All atomic m.s.d.'s increase monotonously with temperature rise. The m.s.d.'s of the B atom show a unique temperature dependence. At lower temperatures the B atom prefers to vibrate along [111], but this preference is reduced with a temperature rise up to 630 K, above which the m.s.d. normal to [111] becomes dominant.

Powder X-ray diffraction of escitalopram oxalate oxalic acid hydrate, (C20H21FN2O)2(C2O4)(H2C2O4)(H2O)0.16

2021 ◽  
pp. 1-2
Author(s):  
James A. Kaduk ◽  
Amy M. Gindhart ◽  
Thomas N. Blanton
Keyword(s):  
Oxalic Acid ◽  
Water Molecule ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Mean Square ◽  
X Ray Diffraction ◽  
Powder Diffraction File ◽  
X Ray ◽  
Single Crystal Structures ◽  
Acid Hydrate

Commercial escitalopram oxalate crystallizes as a hydrated adduct with oxalic acid, in the space group P21 with a = 8.029897(21), b = 25.09397(6), c = 11.138930(31) Å, β = 106.7759(2)°, V = 2148.992(7) Å3, and Z = 4. The agreement of the Rietveld and previous single-crystal structures is excellent; the root-mean-square Cartesian displacements of the non-H atoms of the two independent cations are 0.076 and 0.067 Å, respectively. The water molecule refined to a slightly different position and occupancy. The pattern is included in the Powder Diffraction File™ (PDF®) as entry 00-064-1507.

Octahedral tilting in Pb-based relaxor ferroelectrics at high pressure

2010 ◽  
Vol 66 (3) ◽  
pp. 280-291 ◽  
Author(s):  
Bernd J. Maier ◽  
Ross J. Angel ◽  
William G. Marshall ◽  
Boriana Mihailova ◽  
Carsten Paulmann ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Ambient Pressure ◽  
Relaxor Ferroelectrics ◽  
Partial Ordering ◽  
X Ray Diffraction ◽  
Threefold Axis ◽  
X Ray ◽  
Octahedral Cation

We have employed a combination of powder neutron diffraction and single-crystal synchrotron X-ray diffraction to characterize the pressure-induced phase transitions that occur in the perovskite-type relaxor ferroelectric PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PST-Ba). At ambient pressure the symmetry of the average structure for both compounds is Fm\bar{3}m as a result of partial ordering of the Sc and Ta cations on the octahedral sites. At pressures above the phase transition both the neutron and X-ray diffraction patterns exhibit an increase in the intensities of h,k,l = all odd reflections and no appearance of additional Bragg reflections. Synchrotron single-crystal X-ray diffraction data show that the intensity of hhh peaks, h = 2n + 1, does not change with pressure. This indicates that the structural distortion arising from the phase transition has a glide-plane pseudo-symmetry along the 〈111〉 cubic directions. Rietveld refinement to the neutron powder data shows that the high-pressure phase has either R\bar{3}c or R\bar{3} symmetry, depending on whether the presence of 1:1 octahedral cation ordering is neglected or taken into account, and comprises octahedral tilts of the type a − a − a − that continuously evolve with pressure. The cubic-to-rhombohedral transition is also marked by a large increase in the anisotropy of the displacement ellipsoids of the Pb cations, indicating larger displacements of Pb cations along the rhombohedral threefold axis rather than within the perpendicular plane. For PST the anisotropy of the Pb displacement parameters decreases at approximately 3 GPa above the phase-transition pressure. For both PST and PST-Ba the average magnitudes of Pb-cation displacements expressed in terms of isotropic displacement ellipsoids gradually decrease over the entire pressure range from ambient to 7.35 GPa.

Electron Microscopy of Shock Loaded Polycrystalline Beryllium

1974 ◽  
Vol 32 ◽  
pp. 506-507 ◽  
Author(s):  
J. M. Galbraith ◽  
L. E. Murr ◽  
A. L. Stevens
Keyword(s):  
Electron Microscopy ◽  
Wave Propagation ◽  
Structural Change ◽  
Single Crystal ◽  
Diffraction Pattern ◽  
Shock Loading ◽  
Slip Systems ◽  
Compression Tests ◽  
X Ray Diffraction ◽  
X Ray

Uniaxial compression tests and hydrostatic tests at pressures up to 27 kbars have been performed to determine operating slip systems in single crystal and polycrystal1ine beryllium. A recent study has been made of wave propagation in single crystal beryllium by shock loading to selectively activate various slip systems, and this has been followed by a study of wave propagation and spallation in textured, polycrystal1ine beryllium. An alteration in the X-ray diffraction pattern has been noted after shock loading, but this alteration has not yet been correlated with any structural change occurring during shock loading of polycrystal1ine beryllium.This study is being conducted in an effort to characterize the effects of shock loading on textured, polycrystal1ine beryllium. Samples were fabricated from a billet of Kawecki-Berylco hot pressed HP-10 beryllium.

Crystal structure of an inclusion complex between chiral monoaza-15-crown-5 and S(–)-1-phenyl-ethyl ammonium percholorate

2003 ◽  
Vol 218 (5) ◽  
Author(s):  
Süheyla Özbey ◽  
F. B. Kaynak ◽  
M. Toğrul ◽  
N. Demirel ◽  
H. Hoşgören
Keyword(s):  
Crystal Structure ◽  
Inclusion Complex ◽  
Single Crystal ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
New Type

AbstractA new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group

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