Superionic State Discovered in Ternary Hypervalent Silicon Hydrides via Sodium inside the Earth

TL;DR

This study uses ab initio calculations to discover a new superionic state in Na2SiH6 under Earth's extreme conditions, revealing novel hypervalent silicon hydrides and suggesting potential for similar states in Earth's interior.

Contribution

The paper reports the discovery of a previously unknown superionic state in Na2SiH6 and identifies new hypervalent Si-H anions, expanding understanding of Earth's interior chemistry.

Findings

Identification of a new superionic phase Na2SiH6.

Discovery of novel hypervalent Si-H anions.

Potential existence of similar states inside the Earth.

Abstract

Superionic states are phases of matters that can simultaneously exhibit some of the properties of a fluid and of a solid. Superionic states of ice, H$_{3}$O, He-H$_{2}$O or He-NH$_{3}$ compounds have been reported in previous works. Silicon, sodium, and hydrogen are abundant elements inside the earth. Here, we use ab initio calculations to show that, at extreme conditions inside the earth, Na, Si, and H can form many hypervalent compounds that some of them can exist every close to ambient pressure, and surprisingly a previously unknown type of superionic state of $P\overline3m1 - $Na$_{2}$SiH$_{6}$ can form as well. Our work focused on new superionic state of Na$_{2}$SiH$_{6}$, and the results also reveal several different hypervalent Si-H anions discovered, which are different from individual SiH$_{5}^{\,-}$ and octahedral SiH$_{6}^{\,2-}$ in previous research of ternary alkali hypervalent silicon hydrides. Our work provides some advice on further investigations on potential ternary hydrides inside the earth.