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Influence of ordered carbon‐vacancy networks on the electronic structures and elastic properties of Nb 4 AlC 3− x
Author(s) -
Zhang Hui,
Hu Tao,
Li Zhaojin,
Zhang Yanhui,
Hu Minmin,
Wang Xiaohui,
Zhou Yanchun
Publication year - 2017
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.14559
Subject(s) - vacancy defect , materials science , shear modulus , condensed matter physics , fermi level , bulk modulus , carbon fibers , elastic modulus , anisotropy , modulus , crystallography , composite material , chemistry , quantum mechanics , composite number , electron , physics
Carbon‐vacancy‐bearing Nb 4 AlC 3− x has the best high‐temperature mechanical robustness among MAX phases. The existing form of the vacancies has been long overlooked. Recently, the vacancies in Nb 4 AlC 3− x have been identified to be ordered, establishing an ordered compound Nb 12 Al 3 C 8 . Here, the spatial distribution of the ordered vacancies and their influences on bonding characteristics and elastic properties are unraveled by thoroughly comparing Nb 12 Al 3 C 8 and vacancy‐free Nb 4 AlC 3 . In Nb 12 Al 3 C 8 , the carbon vacancies break only relatively weak Nb–C bonds and form ordered equilateral triangular carbon‐vacancy networks ( OETCVN s) to maximize the bond strengthening effect. The networks slightly shift partial and total density of states toward the Fermi energy level, and bring about a feature of “de‐metallization”. Meanwhile, the presence of OETCVN s results in the softening of elastic modulus, decreasing of the anisotropy of Young's modulus, yet increasing that of shear modulus. These results shed lights on the carbon‐vacancy ordering behavior of MAX phases, and provide an opportunity to tailor their electronic structures and elastic properties through defect engineering.