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## Homework Statement

Calculate the fraction of lattice sites that are Schottky defects for cesium chloride at its melting temperature (645C). Assume an energy for defect formation of 1.86eV.

## Homework Equations

Number of lattice sites per cubic meter (N)

N=(NA[tex]\rho[/tex])/(ACS + ACL)

Where NA = Avogadros number, [tex]\rho[/tex] = density, ACS = 132.91 g/mol and ACL = 35.45 g/mol

Equilibrium number (NS)

NS = N * e^(-QS/2kT)

Where QS = Schottky defect, k = Boltzmanns Constant, and T = temp in Kelvin

## The Attempt at a Solution

I found the density of Cesium Chloride to be 3.99 g/cm^3

N = (6.02.10^23 atoms/mol)(3.99 g/cm^3)(10^6 cm^3/m^3)/(132.91 g/mol + 35.45 g/mol)

From this is I got 1.43 x 10^28 lattice sites/m^3

When I plug this into the NS equation I get 1.16 x 10^24, and I know this is wrong. I am supposed to solve for a NS/N ratio, and the correct answer is 7.87 x 10^-6.

I am not sure what to do here, any help would be appreciated. Thanks