= Solution
At fixed <number density>, attempt <frequency>, nearest-neighbour distance and barrier, the conductivities have ratio \b[$\sigma_{\rm sc}:\sigma_{\rm bcc}:\sigma_{\rm fcc}=1:4/3:2$]. Thus the face-centred cubic array is largest. Numerically,
$$
F=10^{13}\exp\!\left[-\frac{0.35}{(8.61733\times10^{-5})(300)}\right]\simeq1.32\times10^7\ \mathrm{s^{-1}},
$$
$$
\boxed{\sigma_{\rm fcc}=\frac{2nQ^2Fa^2}{k_BT}\simeq1.47\times10^{-7}\ \mathrm{S\,m^{-1}}}.
$$
The small value is consistent with the low supplied carrier <number density> and strongly activated hopping. This comparison holds $n$ fixed rather than comparing fully occupied <crystal structures>, whose site densities at the same neighbour distance differ.
Back to article page
