On the formation mechanisms and properties of MAX phases: A review

Abstract

MAX phases are a family of ternary carbide or nitride ceramics possessing a layered crystal structure and, due to their chemical bonds having a mixed covalent-ionic-metallic nature, have unique properties combining those of metals and ceramics. In this review, the formation mechanisms of MAX phases from elemental and compound powders are reviewed in detail, as the formation mechanisms are closely related to the unique properties of wellsynthesized MAX phases. The stability of MAX phases in some harsh external environments is significantly influenced by the defect population, allowing the mechanisms of defect formation and migration to strongly influence their self-healing performance and radiation tolerance. The properties of MAX phases can be tailored by creating solid solutions, which have lattice distortions, and texturing which results in the preferential orientation of plate-like grains.

High‐Entropy Carbonitride MAX Phases and Their Derivative MXenes

“…[ 1–4 ] Typically, MAX phases possess a unique hexagonal crystalline structure with a space group of P 6 3 / mmc , in which strong covalent bonded M n+1 X n atomic layers are interleaved by A layers via weak metallic bonds, enabling MAX phases with good oxidation resistance, high electrical and thermal conductivities, holding great potential in the fields of mechanics, electrics, and protective coatings. [ 2,5–8 ] In a recent decade, MAX phases have been widely utilized to synthesize their derivative 2D MXenes (M n+1 X n T x , T is the surface functional group) by selective extraction of A layers. [ 9–13 ] The resultant ultrathin MXene layers, featured with high electrical conductivity, tunable surface terminations, and good hydrophilicity, have been extensively investigated in broad applications such as catalysis and energy storage.…”

Synthesis and Characterization of a Nearly Single Bulk Ti2AlN MAX Phase Obtained from Ti/AlN Powder Mixture through Spark Plasma Sintering

“…MAX phases are a relatively new class of advanced ceramics that adopted this name due to the general formula that describes them, M n+1 AX n , where n = 1, 2, or 3, M is an early transition metal, A is an IIIA/IVA-group element and X is C and/or N. These ternary carbides or nitrides combine some of the properties of ceramics and metals, exhibiting high electrical and thermal conductivities, good thermal shock resistance, superior oxidation/corrosion resistance and ease of machining [ 1 , 2 ]. These combined properties, which emanate from their atomic bonding and the nature of the crystalline structure, make them potential candidate materials to be used in advanced technological applications under severe conditions, such as high temperature, aggressive corrosion environment, and high irradiation in aerospace or nuclear systems [ 3 , 4 , 5 ].…”

Adsorption and Activation of CO2 on Nitride MXenes: Composition, Temperature, and Pressure effects

“…[18] All MXenes exhibit a M n + 1 X n T x general formula, where M is as early transition metal, X=C or N, n defines the MXene width (normally n = 1-3), and T x represents one of the common terminations, most often À O, À OH, À F, or À H, [19] that are inherent to their synthesis process. The synthesis of MXenes follows a top-down approach by a selective disassembly of the MAX phase precursors; see the recent review by Zhang et al [20] In the MAX phase, A stands for Al, Si, or other elements in p-block. The removal of A from the MAX phase is achieved by using different chemical etchants.…”