Diffuse scattering and ordering in the short-range modulated paraelectric phase of sodium nitrite, NaNO2

2005 ◽  
Vol 61 (5) ◽  
pp. 473-480 ◽  
Author(s):  
K. Łukaszewicz ◽  
A. Pietraszko ◽  
M. Kucharska
Keyword(s):  
Crystal Structure ◽  
Diffraction Pattern ◽  
Sodium Nitrite ◽  
Diffuse Scattering ◽  
Short Range ◽  
Paraelectric Phase ◽  
Antiferroelectric Phase ◽  
Modulated Structures ◽  
Discontinuous Phase ◽  
Uniform Polarity

The incommensurately modulated antiferroelectric phase of sodium nitrite, NaNO2, transforms at TN = 437.7 K to the short-range modulated paraelectric phase. The apparently discontinuous phase transition is accompanied by characteristic changes in the diffraction pattern. Contrary to the well known modulated structures with sharp satellite reflections, the diffraction pattern of a short-range modulated structure contains diffuse satellite reflections. The short-range modulated crystal structure of the paraelectric phase of sodium nitrite has been analysed by the Reverse Monte Carlo (RMC) simulation of X-ray diffuse scattering. The crystal structure of sodium nitrite may be regarded as consisting of [Na+NO_2^{-}]∞ rows running along the polar b axis. One can expect long fragments of rows with uniform polarity The assumption that single [Na+NO_2^-]∞ rows are polar with uniform polarity proved to be a convenient approximation which is in good agreement with the observed diffraction pattern. The distribution of (+)- and (−)-[Na+NO_2^-]∞ polar rows crossing the (010) plane of short-range modulated NaNO2 revealed by RMC shows nanodomains consisting of distorted fragments of a sinusoidally modulated crystal structure. The size of the nanodomains and the degree of order in paraelectric NaNO2 decreases with temperature.

Diffuse scattering and short-range order in uranium iodine phthalocyanine [U1−x Pc2]I2−y and the X-ray structure analysis of crystals with diffuse superstructure reflections

2003 ◽  
Vol 59 (3) ◽  
pp. 384-392 ◽  
Author(s):  
J. Krawczyk ◽  
A. Pietraszko ◽  
R. Kubiak ◽  
K. Łukaszewicz
Keyword(s):  
Crystal Structure ◽  
Structure Analysis ◽  
Diffuse Scattering ◽  
Short Range ◽  
Short Range Order ◽  
Crystal Structure Analysis ◽  
Range Order ◽  
Small Range ◽  
X Ray ◽  
Unit Cells

Crystals of uranium iodine phthalocyanine present an example of a disordered commensurate modulated structure of the intergrowth type. The short-range order of both uranium ions and iodine chains [I_3^-] n has been analysed by Reverse Monte Carlo (RMC) simulation of X-ray diffuse scattering. The diffraction pattern of uranium iodine phthalocyanine contains diffuse superstructure reflections. In the routine crystal structure analysis diffuse superstructure reflections may be either omitted or measured and classified along with other Bragg reflections. The crystal structure of uranium iodine phthalocyanine is an example of such ambiguity. The crystal structures of two specimens of [U1−x Pc2]I2−y with slightly different composition have been published in the literature with different space groups and unit cells. We have shown that the structure of both specimens differs only in the degree of short-range order and is isostructural with [YbPc2]I2. We have also shown that while the omission of diffuse reflections results in the average crystal structure, the treatment of these reflections as normal Bragg reflections is incorrect and produces the structure averaged over a limited small range.

scholarly journals Diffuse single-crystal scattering corrected for molecular form factor effects

2017 ◽  
Vol 73 (3) ◽  
pp. 231-237 ◽  
Author(s):  
Ella Schmidt ◽  
Reinhard B. Neder
Keyword(s):  
Form Factor ◽  
Single Crystal ◽  
Diffraction Pattern ◽  
Diffuse Scattering ◽  
Short Range ◽  
Short Range Order ◽  
Molecular Form ◽  
Molecular Crystals ◽  
Novel Technique ◽  
Two Component

This paper shows that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor from the diffraction pattern. This novel technique is demonstrated by analysing the diffuse scattering of tris-tert-butyl-1,3,5-benzene tricarboxamide.

scholarly journals Mg(H2O)2[TeO2(OH)4]: a polytypic structure with a two-mode disordered stacking arrangement

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Berthold Stöger ◽  
Hannes Krüger ◽  
Matthias Weil
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Diffraction Pattern ◽  
Correlation Coefficient ◽  
Structure Factor ◽  
Diffuse Scattering ◽  
Small Contribution ◽  
Adjacent Layer ◽  
Absolute Value ◽  
Diffraction Patterns

Crystals of the hydrous magnesium orthotellurate(VI) Mg(H2O)2[TeO2(OH)4] were grown by slow diffusion of an aqueous MgCl2 solution into a KOH/Te(OH)6 solution immobilized in gelatin. The crystal structure is built of sheets of nearly regular corner-sharing [MgO6] and [TeO6] octahedra. Half of the bridging O atoms are connected to disordered H atoms, which are located in rhomboidal voids (long and short diameters of ∼5.0 and ∼2.5 Å, respectively) of these layers. Moreover, the TeVI atom connects to two OH− ions and the MgII atom to two H2O molecules. The OH− ions and H2O molecules connect adjacent layers forming a disordered hydrogen-bonding network. In a given layer, an adjacent layer may be positioned in four ways, which can be characterized by one of two origin shifts and one of two orientations with respect to [100]. The crystals feature a disordered stacking arrangement, leading to rods of diffuse scattering in the diffraction pattern. The polytypism is explained by application of the order–disorder (OD) theory. Different refinement models are compared and the diffuse scattering is evaluated with structure factor calculations. The correlation coefficient of subsequent origin shifts is ∼ −0.33, whereas the orientation of the layers is essentially random. Determining the latter is particularly difficult owing to a small contribution to the diffraction pattern and virtually indistinguishable diffraction patterns for pairs of correlations with the same absolute value. On longer standing in a glass vial, an ordered polytype forms.

Transmission Electron Microscopy studies of the vacancy ordering in YSI2-X thin films

1991 ◽  
Vol 49 ◽  
pp. 562-563
Author(s):  
F.-R. Chen ◽  
T. L. Lee ◽  
L. J. Chen
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Thin Films ◽  
Diffraction Pattern ◽  
Annealing Temperature ◽  
Lattice Mismatch ◽  
Si Substrate ◽  
Metal Thin Films ◽  
Transmission Electron ◽  
Vacancy Ordering

YSi2-x thin films were grown by depositing the yttrium metal thin films on (111)Si substrate followed by a rapid thermal annealing (RTA) at 450 to 1100°C. The x value of the YSi2-x films ranges from 0 to 0.3. The (0001) plane of the YSi2-x films have an ideal zero lattice mismatch relative to (111)Si surface lattice. The YSi2 has the hexagonal AlB2 crystal structure. The orientation relationship with Si was determined from the diffraction pattern shown in figure 1(a) to be and . The diffraction pattern in figure 1(a) was taken from a specimen annealed at 500°C for 15 second. As the annealing temperature was increased to 600°C, superlattice diffraction spots appear at position as seen in figure 1(b) which may be due to vacancy ordering in the YSi2-x films. The ordered vacancies in YSi2-x form a mesh in Si plane suggested by a LEED experiment.

The crystal structure of sodium nitrite

1952 ◽  
Vol 5 (1) ◽  
pp. 132-135 ◽  
Author(s):  
G. B. Carpenter
Keyword(s):  
Crystal Structure ◽  
Sodium Nitrite

Crystal and powder XRD data of Mg3(PO4)2-III: High-temperature and high-pressure form

1995 ◽  
Vol 10 (4) ◽  
pp. 293-295 ◽  
Author(s):  
F. Brunet ◽  
C. Chopin ◽  
A. Elfakir ◽  
M. Quarton
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
High Temperature ◽  
Single Crystal ◽  
Diffraction Pattern ◽  
Structure Refinement ◽  
Powder Xrd ◽  
Single Crystal Structure ◽  
Crystal Structure Refinement ◽  
Pressure Form

A new diffraction pattern of the high-temperature and high-pressure polymorph Mg3(PO4)2-III (PDF 43-500) is given and indexed on the basis of a single-crystal structure refinement. It allows diffractogram indexing of the isostructural high-temperature and high-pressure form of Co3(PO4)2 (PDF 43-499).

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