12-35
12.30 This problem asks that we compute the number of Frenkel defects per cubic meter in silver chloride at 350 ° C. Solution of this problem is possible using Equation 12.2. However, we must first determine the value of
N , the number of lattice sites per cubic meter, which is possible using a modified form of Equation 4.2; thus
N =
A
Ag
N
A
ρ
+ A
Cl
=
(6.023 × 10
23
atoms/mol)(5.50 g/cm
3
)(10
6
cm
3
/ m
3
)
107.87 g/mol + 35.45 g/mol
= 2.31 x 10
28
lattice sites/m
3
And, finally the value of N fr
is computed using Equation 12.2 as
N fr
= N exp
⎛
⎜
⎝
−
Q fr
2 kT
⎞
⎟
= (2.31 × 10
28
lattice sites/m
3
⎢
⎡
⎢
⎣ (2)(8.62 × 10
-5
1.1 eV
eV/K)(350 + 273 K)
⎤
⎥
⎥
= 8.24 x 10
23
defects/m
3
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