Raman spectroscopy of sodium chloride under high-pressure and high-temperature

TL;DR

This study uses Raman spectroscopy to explore the high-pressure and high-temperature behavior of NaCl, revealing its decomposition into new compounds and highlighting the effects of non-equilibrium states and catalysts.

Contribution

It provides new insights into NaCl decomposition and formation of exotic compounds under extreme conditions using advanced high-pressure and high-temperature techniques.

Findings

NaCl decomposes to NaCl3 and Na3Cl above 31 GPa

High temperature and non-equilibrium states influence decomposition pathways

Catalytic effects of transition metal oxides promote chemical reactions

Abstract

The high-pressure and high-temperature behaviors of sodium chloride (NaCl) have the fundamental and application significance to the high pressure physics and chemistry. To explore the reactivity of NaCl at high pressure and high temperature, we compressed the NaCl samples to pressures up to 85 GPa and heated them to a temperature of 1800 by using the diamond anvil cell and the double-sided laser heating technology. Our investigation of Raman spectroscopy shows that NaCl decomposes to NaCl3 with orthorhombic Pnma structure plus possible Na3Cl with tetragonal P4/mmm structure above 31 GPa. It shows that the competition of the unusual Cl-Cl covalent bond and Na-Na metallic bond with the Na-Cl ionic bond at high pressure and high temperature may prefer the occurrence of the NaCl3 and Na3Cl combination. We speculate that the large temperature gradient in the NaCl sample layers in the diamond anvil cell experiments, which indicate a non-equilibrium state, is critical to the decomposition reaction of NaCl observed in this study. The catalytic effect of the used laser absorbing materials of transition metal oxides could be another factor to promote the chemical reaction of NaCl. The results of this investigation provide a new pathway to investigate the distinctive non-1:1 stoichiometric alkali metal-halogen compounds that may have exotic properties.