Rietveld powder structure refinement of Na2Al2Ti6O16; Comparison of synchrotron radiation and conventional x-ray tube datasets

1990 ◽  
Vol 5 (7) ◽  
pp. 1538-1543 ◽  
Author(s):  
H. Toraya ◽  
N. Masciocchi ◽  
W. Parrish
Keyword(s):  
Crystal Structure ◽  
Synchrotron Radiation ◽  
Chemical Analysis ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Site Occupancy ◽  
Partial Ordering ◽  
Crystal Data ◽  
X Ray ◽  
Octahedral Sites

The crystal structure of Na2Al2Ti6O16 was refined by the Rietveld method using synchrotron radiation and conventional x-ray powder data, and the agreement factors were Rp = 3.35%, Rwp = 4.30%, and RBragg = 6.39% for synchrotron data. The formula based on the chemical analysis and 16 O atoms is Na1.97Al1.82Ti6.15O16. The crystal data are monoclinic, C2/m, a = 12.1239(3) Å, b = 3.7749(1) Å, c = 6.4180(2) Å, β = 107.59(1)°, V = 280.00(4) Å3, Z = 1, and Dx = 3.82 g cm−3. The site occupancy refinement showed a partial ordering of Al3+ and Ti4+ ions in the two-crystallographically independent octahedral sites.

Crystal structure of potassium tetraperoxomolybdate (VI) K2[Mo(O2)4]

2005 ◽  
Vol 20 (3) ◽  
pp. 203-206 ◽  
Author(s):  
M. Grzywa ◽  
M. Różycka ◽  
W. Łasocha
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Crystal Structure Refinement ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters

Potassium tetraperoxomolybdate (VI) K2[Mo(O2)4] was prepared, and its X-ray powder diffraction pattern was recorded at low temperature (258 K). The unit cell parameters were refined to a=10.7891(2) Å, α=64.925(3)°, space group R−3c (167), Z=6. The compound is isostructural with potassium tetraperoxotungstate (VI) K2[W(O2)4] (Stomberg, 1988). The sample of K2[Mo(O2)4] was characterized by analytical investigations, and the results of crystal structure refinement by Rietveld method are presented; final RP and RWP are 9.79% and 12.37%, respectively.

Ideal and Real Structure of Ti5O4(PO4)4: X-ray and HRTEM Investigations

1998 ◽  
Vol 54 (6) ◽  
pp. 722-731 ◽  
Author(s):  
F. Reinauer ◽  
R. Glaum
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Structure Refinement ◽  
Ideal Structure ◽  
Crystal Data ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
The Ideal

The crystal structure of pentatitanium tetraoxide tetrakis(phosphate), Ti5O4(PO4)4, has been determined and refined from X-ray diffraction single-crystal data [P212121 (No. 19), Z = 4, a = 12.8417 (12), b = 14.4195 (13), c = 7.4622 (9) Å (from Guinier photographs); conventional residual R 1 = 0.042 for 2556 Fo > 4σ(Fo ), R 1 = 0.057 for all 3276 independent reflections; 282 parameters; 29 atoms in the asymmetric unit of the ideal structure]. The structure is closely related to those of β-Fe2O(PO4)-type phosphates and synthetic lipscombite, Fe3(PO4)4(OH). While these consist of infinite chains of face-sharing MO6 octahedra, in pentatitanium tetraoxide tetrakis(phosphate) only five-eighths of the octahedral voids are occupied according to □3Ti5O4(PO4)4. Four of the five independent Ti4+O6 show high radial distortion [1.72 ≤ d(Ti−O) ≤ 2.39 Å] and a typical 1 + 4 + 1 distance distribution. The fifth Ti4+O6 is an almost regular octahedron [1.91 ≤ d(Ti−O) ≤ 1.98 Å]. Partial disorder of Ti4+ over the available octahedral voids is revealed by the X-ray structure refinement. High-resolution transmission electron microscopy (HRTEM) investigations confirm this result.

A single-crystal neutron and X-ray diffraction study of a Li, Be-bearing brittle mica

2014 ◽  
Vol 78 (1) ◽  
pp. 55-72 ◽  
Author(s):  
G. D. Gatta ◽  
G. Nénert ◽  
G. Guastella ◽  
P. Lotti ◽  
A. Guastoni ◽  
...  
Keyword(s):  
Chemical Analysis ◽  
Single Crystal ◽  
Scattering Length ◽  
Structure Refinement ◽  
Site Occupancy ◽  
Emission Spectrometry ◽  
X Ray Diffraction ◽  
Plasma Atomic Emission Spectrometry ◽  
X Ray ◽  
Final Population

AbstractThe crystal chemistry of a meso-octahedral Li,Be-bearing mica from the Harding pegmatite (Dixon, Taos County, New Mexico, USA) has been investigated by constant-wavelength single-crystal neutron diffraction at 20 K, single-crystal X-ray diffraction at 100 K and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The chemical composition based on ICP-AES analysis leads to the following chemical formula (calculated on the basis of 12 oxygen atoms):Ca(Na0.26K0.04Ca0.69)∑0.99M(Li0.29Mg0.03Fe0.023+Al1.78)∑2.12T(Al1.73Be0.16Si2.11)S4.00O12H2.53. The apparent excess of H is probably due to the fact that the fraction of H2O was assumed by difference to 100 wt.%, and slightly overestimated. On the basis of the previous experimental findings on Li,Be-bearing mica, X-ray (at 100 K) and neutron (at 20 K) structure refinements were performed in the space groupsCcandC2/c. The neutron structure refinement in the space groupCcoffers a view about the (Al,Be,Si)-tetrahedral ordering: the best fit of the refinement was reached with theT1 andT4 sites occupied by (Be + Al) andT2 andT3 fully occupied by Si. This leads to a final population ofT(Al1.88Be0.12Si2.00)∑4.00p.f.u., in reasonable agreement with the chemical analysis. The neutron refinement provides unambigous evidence of the occurrence of Li at theM1 site. The refined fraction of Li at theM1 site ranges between 0.27 and 0.29 a.p.f.u., in excellent agreement with the chemical analysis. The presence of Li, at least at a significant level, at theM2 (andM3) site can be ruled out, as a full site occupancy with the scattering length of Al was obtained. The location of the H sites and the complex hydrogen-bonding scheme are described. A comparison between the structure features of this Li,Be-mica and other brittle micas is carried out.

Crystal-structure refinement of a Zn-rich kupletskite from Mont Saint-Hilaire, Quebec, with contributions to the geochemistry of zinc in peralkaline environments

2006 ◽  
Vol 70 (5) ◽  
pp. 565-578 ◽  
Author(s):  
P. C. Piilonen ◽  
I. V. Pekov ◽  
M. Back ◽  
T. Steede ◽  
R. A. Gault
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Structure Refinement ◽  
Crystal Structure Refinement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Sites ◽  
Mixed Ligands ◽  
High Alkalinity ◽  
Ligand Species

AbstractThe chemistry and crystal structure of a unique Zn-rich kupletskite: (K1.55Na0 .21Rb0.09Sr0.01)Σ1.86(Na0.82Ca0.18)Σ1.00(Mn4.72Zn1.66Na0.41Mg0.12)Σ7.00 (Ti1.85Nb0.11Hf0.03)Σ1.99(Si7.99Al0.12)Σ8.11O26 (OH)4(F0.77OH0.23)Σ1.00, from analkalin e pegmatite at Mont Saint-Hilaire, Quebec, Canada has been determined. Zn-rich kupletskite is triclinic, , a = 5.3765(4), b = 11.8893(11), c = 11.6997(10), α = 113.070(3), β = 94.775(2), γ = 103.089(3), R1 = 0.0570 for 3757 observed reflections with Fo > 4σ(Fo). From the single-crystal X-ray diffraction refinement, it is clear that Zn2+ shows a preference for the smaller, trans M(4) site (69%), yet is distributed amongst all three octahedral sites coordinated by 4 O2− and 2 OH− [M(2) 58% and M(3) 60%]. Of note is the lack of Zn in M(1), the larger and least-distorted of the four crystallographic sites, with an asymmetric anionic arrangement of 5 O2− and 1 OH−. The preference of Zn for octahedral sites coordinated by mixed ligands (O and OH) is characteristic of its behaviour in alkaline systems, in contrast to granitic systems where Zn tends to favour [4]-coordinated, OH− and H2O-free sites with only one ligand species (O, S, Cl, B, I). In alkaline systems, [4]Zn is only present in early sphalerite or in late-stage zeolite-like minerals. The bulk of Zn in alkaline systems is present as discrete [6]Zn phases such as members of the astrophyllite, labuntsovite, milarite and nordite groups, a result of the formation of network-forming complexes inthe low-temperature, low-fS2, high-alkalinity and highly oxidizing systems.

scholarly journals Synthesis and Crystal Structure of Nb0.84N

2011 ◽  
Vol 66 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Nancy Frenzel ◽  
Elisabeth Irran ◽  
Martin Lerch ◽  
Alexandra Buchsteiner
Keyword(s):  
Crystal Structure ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Close Packing ◽  
Powder Diffraction Data ◽  
Synthesis And Crystal Structure ◽  
X Ray ◽  
Layer Sequence ◽  
Neutron Powder Diffraction Data ◽  
Metal Layers

A new compound of the composition Nb0.84N was prepared by ammonolysis of NbO2 at 1100 °C. The crystal structure refinement was performed by the Rietveld method using X-ray and neutron powder diffraction data. Nb0.84N crystallizes in the trigonal space group R3m (no. 166) with the lattice parameters a = 298.5(2) and c = 2384.3(4) pm. The niobium atoms form a close packing with a layer sequence which can be described by the Jagodzinski symbol hhc. The nitrogen atoms fill all octahedral voids. Along [001] a sequence of two layers of trigonal NbN6 prisms and one layer of NbN6 octahedra is formed. The nitrogen positions are fully occupied, the niobium positions only partially. Nb0.84N is part of a family of crystal structures between the anti-NiAs and the NaCl type consisting of close-packed metal layers with varying stacking sequences

Rietveld Structure Refinement of Metastable Lithium Disilicate Using Synchrotron X-Ray Powder Diffraction Data From the Daresbury SRS 8.3 Diffractometer

1990 ◽  
Vol 5 (3) ◽  
pp. 137-143 ◽  
Author(s):  
R.I. Smith ◽  
A.R. West ◽  
I. Abrahams ◽  
P.G. Bruce
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Powder Diffraction Data ◽  
X Ray ◽  
New Instrument ◽  
Diffraction Peaks

AbstractThe crystal structure of metastable Li2Si2O5, Fw = 150.05, has been refined by the Rietveld method using high resolution X-ray powder diffraction data recorded at the Daresbury Synchrotron Radiation Source on the new 8.3 diffractometer. Li2Si2O5, in keeping with many compounds of interest to the materials scientist, exhibits relatively broad diffraction peaks. It is important to establish the quality of crystal structure data that may be obtained from such materials on this new instrument. Various functions were used to model the peak shape from this instrument; a split-Pearson VII function appeared to be marginally superior to Pearson VII or Pseudo-Voigt functions. Refinement was carried out using the split-Pearson VII in the space group Pbcn (60) and terminated with a = 5.6871(6), b = 4.7846(5), c = 14.645(1) Å, V = 398.50 Å3, Z=4, Dc= 2.502 gcm−3, Rwp = 17.06, Rex = 14.48 and Χ2 = 1.39. The refined parameters are compared with those obtained from a previous single crystal X-ray determination.

Crystal structure of Cu doped La0.67Ca0.33MnO3 by Rietveld refinement

2004 ◽  
Vol 19 (4) ◽  
pp. 329-332
Author(s):  
H. L. Cai ◽  
X. S. Wu ◽  
F. Z. Wang ◽  
A. Hu ◽  
S. S. Jiang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Magnetic Properties ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structural Changes ◽  
Rietveld Method ◽  
Crystal Data ◽  
Powder Diffraction Data ◽  
Orthorhombic System ◽  
X Ray

The crystal structure of La0.67Ca0.33Mn0.80Cu0.20O3 (LCMCO) compound was determined from laboratory X-ray powder diffraction data and refined by the Rietveld method. LCMCO is isostructural with La0.67Ca0.33MnO3 (LCMO). The crystal data are: La0.64Ca0.36Mn0.82Cu0.18O3.01, Mr=843.80, orthorhombic system, space group Pnma, a=5.4364(1) Å, b=7.6725(2) Å, c=5.4452(1) Å, V=227.124(8)Å3, Z=4, Dx=6.168 g∕cm3. In comparing with the Cu-free compound, subtle structural changes such as bond lengths and bond angles found in the Cu-doped compound may be responsible for the larger effects on the transport and magnetic properties when Cu partially substitutes for Mn in CMCO.

Crystal structure refinement of α-Si3N4using synchrotron radiation powder diffraction data: unbiased refinement strategy

2000 ◽  
Vol 33 (1) ◽  
pp. 95-102 ◽  
Author(s):  
H. Toraya
Keyword(s):  
Crystal Structure ◽  
Synchrotron Radiation ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structural Parameters ◽  
Structure Refinement ◽  
High Angular Resolution ◽  
Powder Diffraction Data ◽  
Counting Statistics

The crystal structure of α-silicon nitride (Si3N4) was refined by the Rietveld method using synchrotron radiation powder diffraction data (wavelength = 1.2 Å) collected at station BL-4B2 in the Photon Factory. A refinement procedure that adopted a new weight function,w= 1/Y_o^e (Yois the observed profile intensity ande≃ 2), for the least-squares fitting [Toraya (1998).J. Appl. Cryst.31, 333–343] was studied. The most reasonable structural parameters were obtained withe= 1.7. Crystal data of α-Si3N4: trigonal,P31c,a= 7.75193 (3),c= 5.61949 (4) Å,V= 292.447 (3) Å3,Z= 4;Rp= 5.08,Rwp= 6.50,RB= 3.36,RF= 2.26%. The following five factors are considered equally important for deriving accurate structural parameters from powder diffraction data: (i) sufficiently large sin θ/λ range of >0.8 Å−1; (ii) adequate counting statistics; (iii) correct profile model; (iv) proper weighting on observations to give a uniform distribution of the mean weighted squared residuals; (v) high-angular-resolution powder diffraction data.

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