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A scheme is proposed for quantifying the electrical character of substances. The mode of conduction of electricity by a substance is characterized by the degree of electrolysis of ionic transport number, t. For metals and semiconductors t=0, for electrolytes, t=1. For mixed conductors a mean value is used over the range for 25 °C to the liquid at the melting point.
The conductivity of a substance is characterized by a simple function (c) of sigmaĦe, its conductivity by an electronic mechanism at 25 °C, and sigma ĦĦi, its conductivity by an ionic mechanism in the liquid state at the melting point. The function puts sigmaĦe and sigma ĦĦi on to a logarithmic scale, and weights them according to 1-t(bar) and t(bar). The volume conductivity is used. All data are at standard pressure and low electric field strength.
The indices t(bar) and c enable a triangular classification of substances to be produced, with three limiting types (metals, electrolytes, and insulators), and three intermediate types (semiconductors, semielectrolytes, and mixed conductors). This classification has a stronger experimental basis than classification according to bond type. Values of t(bar) and c are given for a range of substances.
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