Study of the nature and role of nanoscale order in complex materials

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• Study of the nature and role of nanoscale order
  in complex materials

D.J.Goossens AINSE Research Fellow, ANU Research
School of Chemistry Department of Physics
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An example study PCNB, C6Cl5NO2

• PCNB is one of a series of chloronitrobenzene
  derivatives being studied
• Disordered nature propensity to undergo
  phase-transitions
• Anomalous dielectric properties, NLO.
• DISORDER often strongly affects the electronic
  environment and
• is fundamental to physical properties
• e.g. second harmonic generation.

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Structural details
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The Data (APS)
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Analysis of diffuse scattering
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Constructing the Model
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Size-effect
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Size-effect (2)
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Scatter plots
ClCl
ClN
NN
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Calculated and Observed
calculated
observed
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Conclusions (PCNB)

• We have a model crystal whose ordering reflects
  that in the real system. This provides
  exceptional insight into the structure. For
  example
• NO2 groups do not order, even on short range.
• NO2 groups push each other apart
  (size-effect)
• We get detailed ADPs for each atom, and they
  need not be able to be modelled by ellipsoids.
• We can separate the components of ADPs due to
  the size-effect (static) from other components
  (probably dynamic)
• This gives insight into molecular dynamics in
  the solid state, and deeper structural
  knowledge.
• For example, dielectric properties are not due
  to ordering of NO2 groups.

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Ibuprofen
Using diffuse scattering to study the molecular
conformations and interactions in a
pharmaceutical.
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Observed and Calculated
Observed
Calculated
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Examining the model
Correlations between molecules connected by
contact vectors of type 1 (top row), 2 (middle
row) 3 (bottom row) in the three basal planes
of Ibuprofen.
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Examining the model (2)
Correlations between molecules connected by
contact vectors of type 1 (top row), 2 (middle
row) 3 (bottom row) in the three basal planes
of Ibuprofen.
A scatter plot of the distribution of the values
of the dihedral angles on C3 (f1 ) and O1 (f2 )
that give minimum molecular energy.
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Conclusions (Ibuprofen)

• For Ibuprofen, the strongest contact vector was
  found to coincide with the
  -COOH--HOOC- interaction which dimerises pairs
  of molecules.
• Important molecular degrees of freedom were
  torsional motions of C3 (angle f1 ), O1 (angle
  f2 ) and C11 (angle f3 ).
• Of these, the motions of C1 and O1 interact
  directly but weakly via a cross term in the
  energy, while C3 and C11 are substantially
  negatively correlated
• Between molecules, components of the
  positional coordinates are correlated when
  they coincide with the direction of propagation
  of certain intermolecular contacts.

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