Electrical behavior of sulfur up to 600 kbar—metallic state

Abstract

Using a sintered diamond tipped opposed piston apparatus the electrical resistance behavior of sulfur has been studied to pressures well over 500 kbar and to temperature of a few hundred °C. At about 300 kbar the resistance starts dropping below the cell background value of about 108 ohm and continues to drop with pressure until about 500 kbar where a steady value of about 10 ohm is reached. In this latter state the dR/dT is positive, indicating metallic character. Temperature cycling the specimen at lower pressures yields negative dR/dT, characteristic of semiconduction. The measured activation energy of semiconduction drops linearly with pressure until the metallic state is reached. The resisitivity in the metallic state is about 0.03 ohm cm. The higher temperature behavior in the metallic state was explored by pulse heating for intervals of the order of a hundred microseconds. An abrupt resistance drop occurs at about 600 °C which is probably the melting temperature of the metallic phase.