Atomic structure of materials

Question 1

Stacking faults

Answer 1

Mistakes in the stacking sequence

Question 2

gamma

Answer 2

angle between x and y axis

Question 3

Primitive lattice

Answer 3

Only 1 lattice point per cell

Question 4

Non-primitive lattice

Answer 4

More than 1 lattice point per cell

Question 5

Bravais lattices

Answer 5

14 possible 3D lattices

Question 6

Names for n-fold rotational axes and symbols

Answer 6

2-fold: diad - oval
3-fold: triad - triangle
4-fold: tetrad - square
6-fold: hexad - hexagon

Question 7

Glide plane

Answer 7

A plane along which if you move 1 side by half a lattice spacing, you’ll end up with a mirror plane

Question 8

Screw axis

Answer 8

An axis along which you translate an element up/down as you rotate it

Shorthand: R subscript n
R is the order of the rotation and n is the number of translations to get a full 360 degree rotation
— n is always counted as twisting to the right even if the screw axis rotates to the left —

Symbols the same as for rotational axes but have tails that point in the direction of rotation.

Question 9

Directional cosines

Answer 9

Angles between axes and the normal to a plane

e.g. x-axis: (h/a) * plane spacing