Iron exists in different crystalline forms, depending mainly on the temperature. The room temperature form of iron is α-

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Iron exists in different crystalline forms, depending mainly on
the temperature. The room temperature form of iron is α-Fe, or
ferrite, which has a body-centred cubic structure with lattice
parameter a = 2.87 Å. Above 910°C the stable form of iron is γ-Fe,
or austenite, which has a face-centred cubic structure with lattice
parameter a = 3.57 Å.
(a) Which of the two structures is/are closed packed? Justify
your answer.
(b) Draw each structure In perspective, In projection along the
[001] direction.
(c) How many atoms per cubic unit cell are there in each
case?