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Q.
The lattice parameter of GaAs (radius of $Ga =1.22 \mathring{A}, As =1.25 \mathring{A}$ ) is
The Solid State
Solution:
$\frac{r_{\oplus}}{r_{\ominus}}\left(\text { i. e. }, \frac{r_{ Ga ^{\oplus}}}{r_{ As ^{3-}}}\right)=\frac{1.22 \mathring{A}}{1.25 \mathring{A}}=0.976$
From radius ratio, it is clear that cation( $Ga ^{3+}$ ion) lies in body centered or cubic void, where
$2\left(r_{\oplus}+r_{\ominus}\right)=\sqrt{3} a$
$2(1.22+1.25) \mathring{A}=\sqrt{3} a \Rightarrow a=2.852$