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when structure of iron changes from bcc to fcc, its atomic radius changes. why?

when structure of iron changes from bcc to fcc, its atomic radius changes. why?

Grade:Upto college level

1 Answers

SAGAR SINGH - IIT DELHI
878 Points
13 years ago

Dear student,

First of all, although each FCC and BCC unit cell apparently consist of 14 and 9 atoms, it is the number of atoms WITHIN the unit cell which matters. For instance, the atoms in the corner of unit cells are shared by 8 unit cells, so only one eighth of each corner atoms must be counted. In the case of atoms located in the center of faces, only half of each atom is located within the unit cell of interest. Therefore,

Number of atoms within a FCC unit cell: (8*1/8)+(6*1/2)=4 atoms per unit cell
Number of atoms within a BCC unit cell: (8*1/8)+(1*1)=2 atoms per unit cell

 

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Sagar Singh

B.Tech, IIT Delhi

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