write about the Stacking of square close packed layers
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Answer:
Stacking of square close packed layers generates a three dimensional simple cubic structure. Here, the second layer is placed over the first layer so as to have its spheres exactly above those of the first layer Subsequent square close packed layers are placed one above the other in the same manner. In this arrangement, spheres of all the layers are perfectly aligned horizontally as well as vertically. Hence, all the layers are alike, and are labelled as 'A' layers. This arrangement of layers is described as 'AAAA... ' type. The structure that results on stacking square close packed layers is simple cubic. Its unit cell is the primitive cubic unit cell
There are two ways of stacking the rows.
One way is for the rows to lie one above the other, with one sphere exactly above another.Here the spheres are aligned horizontally as well as vertically. Here each sphere is in contact with four other spheres two on sides, one above and one below. Hence, the coordination number becomes four. If we join the centres of these four spheres, we will get a square. Therefore, this type of close packing is also referred to as square close packing.
The other way is for the spheres of the second row to be seated on the first row in a staggered manner, that is, in the depressions of the first layer.