KBr also crystallises in the rocksalt structure

PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Dielectric and optical properties of solids · Dielectric and optical properties of solids

Solid State Physics, Ch Dielectric response, local fields and ferroelectricity

Problem

KBr also crystallises in the rocksalt structure, with conventional cubic cell side

a=6.60\,\mathrm{\AA}

(4 ion pairs per cell). Tabulated polarisability volumes are

\alpha_p(\mathrm{K^+})=1.33\,\mathrm{\AA^3}

and

\alpha_p(\mathrm{Br^-})=4.10\,\mathrm{\AA^3}

. ((a)) Predict

\varepsilon_\infty

and

n

for KBr from the Clausius-Mossotti relation. ((b)) The measured values are

\varepsilon_\infty=2.36

and

n=1.536

. Give the percentage difference of the predicted

\varepsilon_\infty

from measurement.

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