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this is the question in the solid state physics
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what is the ratio of the lattice constant c and a for a hcp lattice?(1

supposing the atoms to be rigid spheres , what fraction of space is filled
by atoms in the primitive cubic ,fcc,hcp,bcc and diamond lattice?(2

3)
Draw the primitive unit cell within afcc lattice . what distinguishes this cell
from that of the rhombohedral bravais lattice?