1.

How many lattice points are there in one unit cell of each of the following lattice ? (i) Face-centred cubic (ii) Face-centred tetragonal (iii) Body-centred

Answer»

Solution :(i) Face-centred CUBIC :
No. of lattice POINTS = 8(at corners) + 6(at faces)
= 14
No. of ATOMS per unit cell
`= (8 xx 1/8) + (6 xx 1/2)`
`=4`
(ii) Face-centred TETRAGONAL crystal does not exists. For tetragonal crystal system only primitive and body-centred unit cells are common.
(III) Body-centred cubic :
No. of lattice points = 8(at corners) + 1(at body centre)
`= 9`
No. of atoms per unit cell
`= (8 xx 1/8) + 1`
`= 2`.


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