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Phase stability and weak metallic bonding within ternary‐layered borides CrAlB, Cr 2 AlB 2 , Cr 3 AlB 4 , and Cr 4 AlB 6
Author(s) -
Bai Yuelei,
Qi Xinxin,
He Xiaodong,
Sun Dongdong,
Kong Fanyu,
Zheng Yongting,
Wang Rongguo,
Duff Andrew Ian
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16206
Subject(s) - covalent bond , materials science , crystallography , ternary operation , metal , metallic bonding , zigzag , density functional theory , phase (matter) , bond length , chemistry , computational chemistry , metallurgy , geometry , crystal structure , mathematics , organic chemistry , computer science , programming language
To explore the potential for use of the Cr–Al–B borides, Cr 2 AlB 2 , Cr 3 AlB 4 , and Cr 4 AlB 6 as well as hypothetical CrAlB are investigated using density functional theory. In the CrAl(CrB 2 ) n series strong covalent bonding is present between the B and Cr atoms with, significantly, much weaker metallic Cr–Al and B–Al bonds, suggesting similar unusual properties to the MAX phases. The relative stiffness of the weakest and strongest bonds hint at similar unusual properties to the MAX phases with superior damage tolerance expected for hypothetical CrAlB, as evidenced in the lowest Al1–Al2 bond stiffness. The layered nature and metallic bonding are expected to result in high fracture toughness and damage tolerance. Anisotropic compression is demonstrated, with the stiffest axes along the direction of the B–B zigzag‐/hexagonal‐chains and the softest axes determined by an interplay between the soft metallic interlayers and the rigid covalent bonds. In general the elastic moduli in CrAl(CrB 2 ) n increase as a function of n , however, without the price of an increase in density.