Order and disorder in quaternary atomic laminates from first-principles calculations

Area of Science:

• Materials Science
• Solid State Chemistry
• Computational Materials Science

Background:

• MAX phases are a family of ternary carbides and nitrides with unique atomic laminate structures.
• Quaternary MAX phases introduce additional elements, expanding the potential for novel material properties.
• Understanding phase stability is crucial for synthesizing and utilizing these materials.

Purpose of the Study:

• To investigate the phase stability of chemically ordered and disordered quaternary MAX phases.
• To explore new elemental combinations within the MAX phase structure.
• To predict synthesis conditions and potential applications based on phase stability.

Main Methods:

• First-principles calculations to determine phase stability at 0 K.
• Estimation of order-disorder temperatures (Tdisorder) considering configurational entropy.
• Analysis of electronic structure and bonding to explain stability trends.

Main Results:

• Layered chemically ordered structures are stable at 0 K for MAX phases with Group V and VI elements (M = V, Nb, Ta, Cr, Mo, W).
• TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) exhibit high order-disorder temperatures (>1773 K), predicting stability at typical synthesis temperatures.
• Certain phases, initially predicted unstable, can be stabilized in disordered forms at higher temperatures or via non-equilibrium synthesis methods.

Conclusions:

• Chemically ordered quaternary MAX phases enable novel elemental substitutions, offering a pathway to tune material properties.
• The stability of these phases is influenced by factors such as Ti's role in breaking unfavorable M-C stacking and electronegativity differences.
• This research expands the design space for MAX phases, paving the way for new atomic laminates with tailored functionalities.