Optical and electronic properties of dense sodium

Abstract

High-resolution Raman spectroscopy of dense sodium reveals additonal low-energy lattice excitations in the three high-pressure phases $\mathit{cI}16$, $\mathit{oP}8$, and $\mathit{tI}19$ from 108 to 178 GPa. The Raman-active lattice modes indicate profound changes of the chemical bonding in Na upon its transformation to an insulating state ($\mathit{hP}4$ phase) at pressures above 178(2) GPa. The calculated values of the valence electron localization maxima versus pressure provide insights into the experimentally observed solid-solid phase transitions and anomalous melting behavior of sodium.