Imperfections in solids

Question

Statement-I : Density of an ionic solid decreases due to Frenkel defect.

Statement-II: Packing efficiency of simple cubic structure is 52.4%.

Easy

Solution

I) Frenkel defect is a dislocation defect. One of the ion(generally cation) leaves the lattice point and occupies the interstitial site but does not leave the crystal, thus no change in the density of crystal.

Schottky defect is a vacancy defect in which equal number of cations and anions will be missing the lattice points.It leads to decrease in density.

II) Packing efficiency of simple cubic structure is 52.4%.

$\mathrm{P}.\mathrm{E}=\frac{1\times {\displaystyle \frac{4}{3}}{\mathrm{\pi r}}^{3}}{{\left(2\mathrm{r}\right)}^{3}}$

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