Making Metallic Salts at Ultra-High Pressures and Temperatures

Alkali halide KBr is nominally a wide band-gap insulator and a common calibrant, pressure medium and thermal insulator used in laser-heated diamond-anvil cell experiments. At high pressures (~10-70 GPa) and high temperatures (~2500+ K), transparent KBr becomes opaque. Infrared and Raman spectroscopies suggest a semiconducting nature with possible evolution toward the metallic state upon further compression. Upon decompression, KBr opacity decreases becoming fully transparent at ambient conditions.