Observation of Metal-insulator and Metal-Metal Transitions in Hydrogen Iodide under Pressure

Abstract
Hydrogen iodide has been studied up to pressures of 70 GPa at low temperatures in a diamondanvil cell. Electrical-conductivity and optical measurements have been used to observe pressure-induced phase transitions which are interpreted as follows: First a metal-insulator transition takes place in the molecular solid; with increased pressure a metal-metal molecular-to-atomic transition occurs. An additional transition due to intrinsic impurities has been observed. Implications for metallic hydrogen are discussed.