ENGR 240 - 9.5.07

# ENGR 240 - 9.5.07 - ENGR 240 September 5 2007 For unit cell...

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ENGR 240 – September 5, 2007 For unit cell, one edge length in any direction is taken as one unit in that direction o Holds true for unit cells that do not have sides of the same length Determining Direction Indices of Crystallographic directions o Move the vector so that it passes through the origin o Find the length of that vector projection on each axis o Multiply or divide by a common factor to give the smallest possible integers o Place in square brackets [ ] o Express negative vector values as the number with a bar over it Family of equivalent directions o Spacing of atoms is the same in each direction o Expressed with < > o Example: for cubic <1 0 0> = <1 0 0>, <-1 0 0>, <0 1 0>, <0 -1 0>, <0 0 1>, <0 0 -1> Crystallographic Planes o Specify planes with Miller Indices (h k l) o Using Miller indices Move plane off origin (if necessary) by one edge length Determine the axial intercepts Take reciprocal of intercepts Use parentheses to denote NOTE: Parallel planes are equivalent (Identical Indices)

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ENGR 240 - 9.5.07 - ENGR 240 September 5 2007 For unit cell...

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