Important definition in crystallography

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Discussion Overview

The discussion revolves around the definition of a close packed plane in lattice structures, specifically in the context of face-centered cubic (FCC) structures. Participants explore the characteristics that define close packed planes and the conditions under which atomic packing occurs.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on the definition of a close packed plane and its identification in FCC structures.
  • Another participant states that the close packed plane has the smallest interatomic spacing and suggests comparing atomic spacing of different dimensions of the cube.
  • A similar point is reiterated by another participant, who also questions whether a close packing plane means atoms cannot be packed any closer.
  • In response, a participant clarifies that a close packing plane is defined by the closest separation of atoms, but under normal conditions, atoms are not packed closer unless under high pressure.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of what constitutes a close packed plane, particularly regarding the implications of atomic packing under various conditions. The discussion remains unresolved with multiple perspectives presented.

Contextual Notes

Some statements depend on specific definitions of atomic packing and conditions such as pressure, which are not fully explored in the discussion.

kelvin490
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Can anyone tell me what's the definition of close packed plane in lattice structure? How can I be sure the close packed plane in FCC structure is (111) ?
 
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The close packed plane has the smallest (minimum) interatomic spacing.

Compare the atomic spacing of the cube edge (edge of face) with face diagonal and cube diagonal.

This might help - http://www.egr.uri.edu/che/course/che333/Structure.pdf
 
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Astronuc said:
The close packed plane has the smallest (minimum) interatomic spacing.

Compare the atomic spacing of the cube edge (edge of face) with face diagonal and cube diagonal.

This might help - http://www.egr.uri.edu/che/course/che333/Structure.pdf

Does it mean a close packing plane is a plane that the atoms cannot be packed any closer?

Thanks for reply.
 
Last edited by a moderator:
kelvin490 said:
Does it mean a close packing plane is a plane that the atoms cannot be packed any closer?
No - it just means that it is the plane with the closest separation of the atoms.

http://www.jwave.vt.edu/crcd/farkas/lectures/structure.ppt

Under normal conditions, the atoms aren't packed closer. Only under increasingly high pressures would they get closer.
 
Last edited by a moderator:

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