Transition of expanded liquid iron to the nonmetallic state under supercritical pressure

A transition of expanded liquid iron to the nonmetallic state under high pressures (30-100 kbar) at high temperatures (of about 1 eV) is discovered. The result is obtained by direct measurement of the dependence of resistivity on the specific internal energy and volume. Measurements are taken in the specific volume range from the melting curve to values six times higher than the normal specific volume V (0) in the solid state. It is shown that iron remains in the metallic state up to a relative volume of V/V (0) = 3-4, at which the resistivity attains a value of about 3-4 mu I (c) m and becomes almost independent of temperature, while the conduction electron mean free path decreases to the atomic spacing. For V/V (0) = 4-5, a transition to the nonmetallic state takes place, for which the temperature coefficient of resistance becomes negative and its absolute value becomes much higher than in the metallic state.