Hi all, In a periodic array of ions, e.g. a metal crystal, the conduction electrons are free to move around. I have read that distortions to the periodic array can cause a decrease in conductivity of the crystal. These can be crystal impurities, phonons etc. My question is, why should the conductivity change? For example, if we had a perfect gold crystal, and measure the conductivity, it should give a finite value (?). If we then melt this crystal and keep the density more or less the same, we will have less conductivity. This I dont get, the arrangement of the atoms is different, but on average the distance between them is more or less the same, so the average potentials in the two cases are equal, and the electron feels the same forces throughout the crystal. why then are the conductivities different?