Alkali subhalides: high-pressure stability and interplay between metallic and ionic bonds

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Chemistry

Background:

• High pressure dramatically alters material properties and reactivity, leading to the formation of novel compounds.
• Previously, sodium subchlorides (NaxCl, x > 1) were discovered to be stable under high-pressure conditions.

Purpose of the Study:

• To conduct a comprehensive study of alkali subhalides under high pressure.
• To investigate the stability and electronic structure of these novel compounds.
• To develop a predictive model for the stability of high-pressure alkali subhalides.

Main Methods:

• Utilizing evolutionary crystal structure prediction calculations.
• Performing in-depth analysis of crystal and electronic structures.
• Validating the predictive model with calculations on various alkali subhalides (A3Y).

Main Results:

• An updated phase diagram for NaxCl, including the new compound Na4Cl3 and two new phases of Na3Cl.
• Observation of unique electronic structures in sodium subchlorides, including chlorine atoms with a -2 oxidation state.
• Development of a model rationalizing the stability of alkali subhalides at high pressure.

Conclusions:

• The study provides a theoretical framework to understand the stability of high-pressure alkali subhalides.
• The findings challenge existing chemical paradigms by demonstrating the formation of stable, unconventional compounds.
• The developed model successfully predicts the stability of recently reported high-pressure compounds.