What sort of materials are ohmic and what sort of materials are non-ohmic? I have tried looking around on the internet and have not found any clear way to differentiate between ohmic and non-ohmic materials based on their properties. Would I be correct in saying that metals are ohmic; where as semiconductors and non-metals are non-ohmic? (assuming that they are at a constant temperature).
Ohmic conductors are conductors where the current is proportional to the voltage applied across it with all other physical conditions held constant (Temperature being the main one). This is an accurate definition of Ohm's law. The constant of proportionality in this relationship is the same as the resistance.
Any conductor which follows this rule is ohmic, and any conductor that does not is non-ohmic. Simply stating that ohmic conductors should follow the equation V=IR at a constant temperature does not suffice as this relation will be followed by definition of resistance (R=V/I). The real defining quality of an ohmic conductor is that its resistance does not change at a constant temperature.