Electrical resistivity and equation of state measurements on hot expanded aluminum in the metal-nonmetal transition range

Measurements have been performed on aluminum that expanded from the initial solid state by a factor of 6-9 under a supercritical pressure (> 10 kbar). Thin aluminum foil strip (similar to 10 mu m) sandwiched between two sapphire plates (similar to 1 mm) is heated by an electrical current pulse for less than 1 mu s, so that the Joule heat deposited into the sample achieves 4-6 the cohesion energy. Such experimental technique ensures sufficiently homogeneous heating and practically one-dimensional expansion of the foil strip. The current through the sample, the voltage drop across its length, and the pressure near the sample surface are measured. From the measured quantities, the electrical resistivity and pressure, both as functions of density and internal energy, are directly determined. Present results show that the dependence of the electrical resistivity of aluminum on internal energy along isochores acquires a negative slope at a density that is about three times lower than the standard solid density that indicates transition into a nonmetallic state. The equation of state relation obtained in this work evidences that this transition is continuous.