Defect in a Defect

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Defect in a Defect Hierarchy of Defects
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Defect in a Defect!

• This is an interesting concept to explore.
• We will consider some examples to explore this
  concept.
• 0D ? Vacancy is a point defect. Vacancies can
  get ordered to form Vacancy Ordered Phases. ?
  There could be point defect in the Vacancy
  sublattice ? an atom present where a vacancy
  should have been there (Atom is a defect in the
  vacancy sublattice!) ? this is a defect in a
  defect!
• 1D? Dislocation is a defect. ? A kink or a jog
  is a defect in the dislocation line ? a defect in
  a defect.
• 2D? Surface is a defect. ? Defect in a defect ?
  Steps in a surface is a defect in the surface. ?
  Defect in a defect in a defect ? Steps in these
  steps is a defect in the steps

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0D
In a Vacancy Ordered Phase (VOP) there could be a
vacancy in the vacancy sublattice ? this is an
atom!? we can conceive such a hierarchy of
higher order defects!
Vacancy in the vacancy sublattice ? i.e. an atom!
Perfect Ordered Crystal
Vacancy Ordered Phase
Schematics
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1D
We can even further visualize things like a kink
in the jog!
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2D
Defect in the surface
Defect in the Ledges
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Hierarchy of Defects

• This is another interesting concept
• We will try to understand this using the example
  of VOP
• We have seen that an atom is a defect in the
  vacancy sublattice of the VOP.
• These atoms could be randomly present in the
  vacancy sublattice or be ordered in the
  sublattice to give a sub-sublattice
• A defect in this atom sub-sublattice of the
  vacancy sublattice is again a vacancy!
• This process of formation of defects in sub,
  sub-sub can be carried forward and we can
  conceptualize this hierarchy of defects!