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Discuss Diamond structure with neat diagram and also determine the effective number ofatoms/unit cell, co-ordination number and atomic radius in terms of lattice constant.

Mumbai university > FE > SEM 1 > Applied Physics 1

Marks: 5M

Year: May 2015

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Diamond is a metastable allotrope of carbonwhere the each carbon atom is bonded covalently with other surrounding four carbon atoms and are arranged in a variation of the face centered cubic crystal structure called a diamond lattice.

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1) No. of atoms per unit cell-

Corner -1/8 × 8 = 1

Face -1/2 × 6 = 3

Four atoms - 4

Total = 8 atoms

2) Atomic radius-

(XY)2=(XT)2+(YT)2

=(XT)2+(YZ)2+(TZ)2

(2r)2=(a4)2+(a4)2+(a4)2

r=3a8

3) Co-ordination no. is 4

Each carbon atom is in touch with 1 corner & 3 face centered atoms in a tetrahedral fashion, hence co-ordination no. is 4

4) Atomic packing factor vV=0.34=34%

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