Structural - lecture 2
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Why is it not convenient to give coordinates in absolute distances in solid state structures?
They are not readily interpretable
What coordinates are given to solid state structures?
Fractional coordinates
What do projection representations show?
Structure viewed down an axis with the co-ordinates of atoms given only for the out of plane positions
What is close packing of simple solids?
The atoms being tightly arranged together
Where does the second layer get added in close packing?
In between the gaps of atoms
What is the closest packing arrangements possible?
Each sphere touches 6 in its own layer, 3 above and 3 below
What repeating pattern is used in HCP?
ABABABAB…
What repeating pattern is used in CCP?
ABCABCABC…
What are the two 3D structures used?
Hexagonal close packing Cubic close packing
What are the features of the HCP?
Two layer repeat ABABABABA…
What are the features of the CCP?
Three layer repeat ABCABCABC…
What are the two types of holes in the HCP and CCP arrangments?
Octahedral holes Tetrahedral holes
How do you mathematically work out how efficient packing is?
Use the radius to calculate the percentage packed
What three things do you need to use to work out packing efficiency?
SOH CAH TOA Volume of a sphere Hyp² equation
What is the equation for volume of a sphere?
4/3 π r³
What is the equation for hyp²?
hyp² = a² + b²