Polymorphism and Polytypism of α-LiNH4SO4 Crystals. Monte Carlo Modeling Based on X-ray Diffuse Scattering

2014 ◽  
Vol 14 (11) ◽  
pp. 5784-5793 ◽  
Author(s):  
Dorota Komornicka ◽  
Marek Wołcyrz ◽  
Adam Pietraszko
Keyword(s):  
Monte Carlo ◽  
Diffuse Scattering ◽  
Monte Carlo Modeling ◽  
X Ray

X-ray diffuse scattering from HMTA: analysis via a Monte Carlo model

2008 ◽  
Vol 64 (4) ◽  
pp. 456-465 ◽  
Author(s):  
D. J. Goossens ◽  
A. P. Heerdegen ◽  
T. R. Welberry
Keyword(s):  
Monte Carlo ◽  
Azelaic Acid ◽  
Diffuse Scattering ◽  
Cross Correlation ◽  
Monte Carlo Model ◽  
Limited Range ◽  
Thermally Induced ◽  
X Ray ◽  
Zero Correlation ◽  
Average Position

Hexamethylenetetramine (HMT, C6H12N4, also referred to as urotropin) and azelaic acid [A, HOOC—(CH2)7—COOH] form a co-crystal or adduct (HMTA, also referred to as urotropin azelate) which exhibits several structural phases as a function of temperature. At room temperature, the structure is orthorhombic, but shows substantial disorder. Here, this disorder is explored by analyzing the diffuse scattering from single crystals of HMTA via Monte Carlo simulation. The disorder is in part occupational, with two orientations of azelaic acid occurring, and in part thermally induced, which is to say dynamic. The occupational disorder can be thought of as a combination of limited-range in-plane (bc plane) negative correlations combined with effectively zero correlation between planes (along a), rather like stacking faults. Size effect, the cross-correlation between molecular orientation and displacement from average position, is required to reproduce the observed diffuse scattering.

scholarly journals Reverse Monte Carlo modeling of the neutron and X-ray diffraction data for new chalcogenide Ge–Sb–S(Se)–Te glasses

2013 ◽  
Vol 74 (10) ◽  
pp. 1355-1362 ◽  
Author(s):  
M. Fabian ◽  
E. Svab ◽  
V. Pamukchieva ◽  
A. Szekeres ◽  
K. Todorova ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Diffraction Data ◽  
Reverse Monte Carlo ◽  
X Ray Diffraction ◽  
Monte Carlo Modeling ◽  
X Ray

scholarly journals The interpretation and analysis of diffuse scattering using Monte Carlo simulation methods

2007 ◽  
Vol 64 (1) ◽  
pp. 23-32 ◽  
Author(s):  
T. R. Welberry ◽  
D. J. Goossens
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Diffuse Scattering ◽  
Simulation Methods ◽  
Neutron Sources ◽  
X Ray ◽  
Average Structure

Studies of diffuse scattering had a prominent place in the first issue ofActa Crystallographica60 years ago at a time when conventional crystallography (determination of the average structure from Bragg peaks) was in its infancy. Since that time, conventional crystallography has developed enormously while diffuse-scattering analysis has seemingly lagged well behind. The paper highlights some of the extra difficulties involved in the measurement, interpretation and analysis of diffuse scattering and plots the progress that has been made. With the advent of the latest X-ray and neutron sources, area detectors and the ever-increasing power of computers, most disorder problems are now tractable. Two recent contrasting examples are described which highlight what can be achieved by current methods.

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