Properties of Electron Energy Band Systems

Metal A material with a partially filled energy band. 

Semiconductor and Insulator A material with filled and empty energy bands (at T = 0°K), and an energy gap Eg between highest filled and lowest empty bands. 

Semimetal A material which formally has only completely filled and completely empty bands, but which has, due to overlap of a formally filled and a formally empty band, two or more partially filled bands and behaves as a metal instead of as a semiconductor or insulator. 

Note that these formal definitions do not involve the conductivity = resistivity i) of the materials, only their energy bands and relative occupation. A short description of the distinguishing properties (231, 232, 436, 437) of each follows  

Simple (free electron theory) metals have a number of other characteristic properties, including  

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