Synthesis of Sodium Polyhydrides at High Pressures

TL;DR

This study reports the first synthesis of sodium polyhydrides NaH3 and NaH7 at high pressures and temperatures, combining experimental and theoretical methods to explore their structure and bonding.

Contribution

It provides the first experimental evidence of sodium polyhydrides with unusual stoichiometry formed at high pressures, validated by combined spectroscopy, diffraction, and ab-initio calculations.

Findings

NaH3 and NaH7 formed above 40 GPa and 2000 K

Stable structures confirmed by experiments and theory

Indications of multicenter bonding in these compounds

Abstract

The only known compound of sodium and hydrogen is archetypal ionic NaH. Application of high pressure is known to promote states with higher atomic coordination, but extensive searches for polyhydrides with unusual stoichiometry remain unsuccessful in spite of several theoretical predictions. Here we report the first observation of formation of polyhydrides of Na (NaH3 and NaH7) above 40 GPa and 2000 K. We combined synchrotron x-ray diffraction and Raman spectroscopy in a laser heated diamond anvil cell and theoretical Ab-Initio Random Structure search, which both agree in stable structures and compositions. Our results support the formation of multicenter bonding in a material with unusual stoichiometry. These results are applicable to the design of new energetic solids and high-temperature superconductors based on hydrogenrich materials.