Abstract
The paper presents accurate experimental results for the electrical conductivity σ, the equation of state and its derivatives such as isothermal compressibility, thermal expansion coefficient and thermal pressure coefficient, as a function of pressure and temperature to 2500 bar and 1580°C, respectively. Special consideration is given to the range of densities d smaller than 9 g cm−3. The results give considerable evidence, that a temperature-dependent mobility gap (E c − E f) occurs for d < 9 g cm−3. The variation of (E c − E f) with d and T, which is determined from a logarithmic plot of σ versus 1/T and the thermoelectric power S, suggests that (E c − E f) vanishes at d about 8.8 g cm−3. The value of σ0 is about 140–200 ohm−1 cm−1 and in excellent agreement with the prediction of Mott (1971).
An attempt is made to analyse the equation-of-state data in terms of a rigid-sphere model. The results indicate the first evidence for a change from metallic cohesion to another interatomic force law in the course of the metal-semiconductor transition.