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Intrinsic hardness of boron carbide: Influence of polymorphism and stoichiometry
Author(s) -
Cheenady Amith Adoor,
Awasthi Amnaya,
Subhash Ghatu
Publication year - 2020
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.17420
Subject(s) - stoichiometry , boron carbide , electronegativity , materials science , boron , covalent bond , bond strength , polymorphism (computer science) , carbide , bond length , density functional theory , thermodynamics , crystallography , computational chemistry , chemistry , metallurgy , composite material , crystal structure , organic chemistry , physics , adhesive , biochemistry , layer (electronics) , genotype , gene
Boron carbide comprises of polymorphs that differ in crystallographic arrangement and stoichiometry. Consequently, specimens extracted from the same batch can exhibit variability in mechanical properties depending on the constituent mixture of polymorphs. In this work, density functional theory simulations and estimates from three models (bond resistance model, bond strength model, and electronegativity model) are utilized to (i) investigate the influence of polymorphism and stoichiometry on the intrinsic hardness of boron carbide, (ii) reveal the sensitivity of the estimates to the model used, and (iii) test their conformance to experimental data. The study finds intrinsic hardness of boron carbide to be primarily a function of stoichiometry, with polymorphism having a lower influence. Furthermore, hardness estimates are shown to exhibit substantial sensitivity to the model used, differing by as much as 9 GPa for the same polymorph. Thus, the search for new superhard materials should be guided by more than just one model. Our analysis finds bond resistance model to offer the best conformance to experimental data, indicating that bond length is a much stronger influencer of intrinsic hardness in covalent crystals than coordination numbers and electronegativities of bonding atoms.