Miller Indices (hklj): Hexagonal Lattice Explained

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Discussion Overview

The discussion revolves around the concept of Miller indices in the context of a hexagonal lattice, specifically focusing on the relationship between the indices (hklj) and the basis vectors of the lattice. Participants explore the implications of redundancy in the indices and seek to clarify the definitions and relationships among the basis vectors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that there are four Miller indices for the hexagonal lattice, with the third being redundant, expressed as l=-(h+k).
  • One participant expresses uncertainty about how the relationship between the basis vectors a1, a2, and a3 leads to the stated relationship among the Miller indices.
  • Another participant suggests that the redundancy in coordinates implies a specific relationship among the indices.
  • There is a question regarding the definition of the basis vectors and whether a3 lies in the same plane as a1 and a2.
  • One participant confirms that the vectors are at a 60-degree angle relative to each other.
  • Another participant emphasizes the need to relate the Miller indices to the coordinates of the lattice vectors intersecting with the plane.
  • There is a mention of an additional vector a4 in the context of the four indices, indicating some confusion about the system.
  • A hint is provided that Miller indices refer to a point in reciprocal space, suggesting the need to construct reciprocal space basis vectors.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and confusion regarding the relationships among the Miller indices and the basis vectors. No consensus is reached on the exact derivation or implications of these relationships.

Contextual Notes

Participants have not fully resolved the mathematical steps necessary to clarify the relationship between the Miller indices and the basis vectors. There are also dependencies on definitions that remain unaddressed.

aaaa202
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There are four miller indices (hklj) for the hexagonal lattice, the third being redudant:

l=-(h+k) (1)

Given the basis vectors a1,a2,a3 I can certainly see that:

a3=-(a1+a2)

But how does this immidiatly lead me to the relation (1) between the miller indices?
 
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Spontaneously, I don't know the answer, but I think it is relatively easy to work out. Have you tried?
If you really encounter problems, we all are willing to help you.
 
The redundancy in coordinate implies the relationship
 
aaaa202 said:
Given the basis vectors a1,a2,a3 I can certainly see that:

a3=-(a1+a2)

But how does this immidiatly lead me to the relation (1) between the miller indices?

How do you define these basis vectors? Is a3 in the same plane as a1 and a2?
 
Yes they are are all with a 60 degree angle relative to each other.
 
The problem is how exactly to relate the miller indices given (-a1+a2)=a3. After all miller indices for a plane are obtained as inverses of the coordinates for the intersection of the lattice vectors with the plabe.
 
Oh, so these are the a1,a2,a3 in the system with four indices. You have and a4 as well. Right?
Sorry, I was confused.
 
yes exactly, 3 vectors in the hexagonal plane, one in the c-direction
 
Hint: Miller indices refer to a point in reciprocal space, hence you have to construct the reciprocal space basis vectors.

G = H a* + K b* + L c*(for the "normal" 3 Miller indices).
 

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