Chemical bonding and electronic-structure in MAX phases as viewed by X-ray spectroscopy and density functional theory

TL;DR

This review discusses the electronic structure and chemical bonding in MAX phases, highlighting how their unique bonding and crystal structure influence their diverse physical properties, with insights from X-ray spectroscopy and density functional theory.

Contribution

It provides a comprehensive analysis of MAX phases' bonding and electronic structure, correlating spectroscopic data with theoretical calculations to understand property tuning.

Findings

MAX phases exhibit a combination of metallic and ceramic properties.

Bonding characteristics influence conductivity, elasticity, and magnetism.

Spectroscopic studies align well with density functional theory results.

Abstract

This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibit a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M-C bonds in high-density MC slabs, and relatively weak M-A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other materials properties makes it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.