Extension of MAX phases from ternary carbides and nitrides (X = C and N) to ternary borides (X = B, C, and N): A general guideline

Abstract

AbstractAlthough significant progress has been made on understanding the structure–property relationship of MAX phases, a clear answer has not been given to the outstanding question whether MAX phases can be extended from carbides and nitrides (X = C and N) to borides (X = B). Herein, based on the systematically investigations on the general trend of lattice constants and elastic properties of the experimentally found MX and M2AX (X = B, C, and N) with the valence electron concentration (VEC), a guideline for the discovery of new MAX borides is given. The MX and M2AX (X = B, C, and N) compounds are situated in a small range of VEC, and their lattice constants generally decrease with VEC. Second‐order elastic constants c11, c33, and bulk modulus B of M2AX (X = B, C, and N) increase with VEC due to enhanced bonding, c44 and G, however, increase up to some critical values and then decline with the further increase of VEC. Based on the electronic structure–elastic property relationship and the presence of rock salt–structured transition metal monoborides, nine possible MAX phase borides M2AB (M = Zr, Hf, Nb, A = P, As, and Sb) are predicted. Thus, MAX phases can be extended from X = C and N to X = B, C, and N.