Metal-insulator transition i and

At zero pressure polymerized RbC(Formula presented) is an insulator, whereas polymerized KC(Formula presented) is a metal with a slight low-temperature resistive upturn. We report measurements of the resistivity of RbC(Formula presented) under pressure, finding a hysteretic resistive transition in RbC(Formula presented) near 200 K at 5 kbar, at which point the material transforms from insulator to metal. Correcting the resistivity to constant volume, both materials are metallic below the transition with a common low-temperature resistive upturn which is suppressed under compression.