Novel stable compounds in the Mg-O system under high pressure

Area of Science:

• Materials Science
• High-Pressure Physics
• Computational Chemistry

Background:

• The magnesium-oxygen (Mg-O) system is fundamental to understanding planetary interiors and material properties under extreme conditions.
• Previous studies have primarily focused on magnesium oxide (MgO), with limited exploration of other stoichiometries at high pressures.

Purpose of the Study:

• To computationally explore the full range of possible stoichiometries for the Mg-O system at pressures up to 850 GPa.
• To identify novel thermodynamically stable Mg-O compounds and analyze their chemical bonding and electronic properties.

Main Methods:

• Utilized ab initio evolutionary simulations to predict stable Mg-O phases.
• Performed detailed chemical bonding analysis, including charge transfer and electron density distribution.
• Calculated electronic band structures to determine material conductivity.

Main Results:

• Identified two new thermodynamically stable compounds: MgO2 at 116 GPa and Mg3O2 at 500 GPa, in addition to MgO.
• MgO2 exhibits peroxide ions [O-O](2-), while Mg3O2 is an electride with non-nuclear electron density maxima acting as anions.
• Mg3O2 possesses a significantly narrower band gap compared to MgO and MgO2, suggesting potential semiconducting properties.

Conclusions:

• The Mg-O system hosts novel stable compounds (MgO2, Mg3O2) under high pressure, expanding known magnesium oxide phases.
• The unique bonding in MgO2 and Mg3O2, including peroxide and electride characteristics, highlights complex chemistry at extreme conditions.
• These findings provide a basis for understanding the existence and properties of Mg-O compounds within planetary interiors.