For each crystal below

PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Crystal structure, bonding and diffraction · Crystal structure, bonding and diffraction

Solid State Physics, Ch Symmetry and the classification of crystals

Problem

For each crystal below, the only operation that matters is a screw axis along

c

, and the reflections considered are

(00l)

, which every rotation about

c

leaves unchanged. ((a)) A tetragonal crystal has a

4_1

screw along

c

. Which of

(001)

(002)

(003)

(004)

and

(008)

are forced to vanish by the screw? ((b)) Answer the same question for a

4_2

screw along

c

. ((c)) Hexagonal close-packed magnesium,

P6_3/mmc

, has a

6_3

screw along

c

. Which of

(001)

(002)

and

(003)

does the screw forbid?

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