Electrical properties of solids

Solids show an extremely wide range of electrical conductivity, and on this basis they are classified into three categories.

i. Conductors : Solids with very high electrical conductivities, in the range $10^{4}$ to $10^{7}\ \Omega^{-1}\,m^{-1}$, are conductors. Metals and electrolytes (ionic solids in the molten state or in aqueous solution) are both conductors: metals conduct by the movement of electrons, electrolytes by the movement of ions.

ii. Insulators : Solids with very low conductivities, in the range $10^{-20}$ to $10^{-10}\ \Omega^{-1}\,m^{-1}$, are insulators. Most nonmetals and molecular solids belong to this category.

iii. Semiconductors : Solids with conductivities intermediate between those of conductors and insulators, in the range $10^{-6}$ to $10^{4}\ \Omega^{-1}\,m^{-1}$, are semiconductors. The metalloids silicon and germanium are the classic examples. …