Publication Date:
2014-06-12
Description:
Spinel phase aluminum oxynitride solid solution (γ-alon, with formula of Al (8+ x )/3 O 4− x N x ) exists in the narrow Al 2 O 3 -rich region of Al 2 O 3 -AlN systems. The first-principles calculations were developed to investigate the composition-dependent bonding and hardness of γ-alon. Six supercell model for Al (8+ x )/3 O 4− x N x ( x = 0, 0.25, 0.44, 0.63, 0.81, and 1) was constructed to perform our calculations with high accuracy. It was found that the lattice constant increases with increasing composition of nitrogen in γ-alon. The bond lengths of Al IV –O, Al VI –O, Al IV –N, and Al VI –N all increase with the expansion of crystal structure. The well-known Mulliken overlap populations were calculated to estimate the bonding and hardness. As the content of nitrogen substitute increases, the Al–N bonds present more covalent characteristic, while the Al–O bonds present more ionic characteristic. The Al IV –N is the hardest bond in γ-alon. The theoretical hardness of γ-alon could be slightly enhanced from 17.16 GPa to 17.97 GPa by increasing content of nitrogen in full solubility range. The contribution ratio, C H μ , was proposed to quantify the contribution of bonds to hardness of γ-alon. The Al–O bonds are found to contribute more to the hardness. The Al–N bonds are the main influencing factor to enhance the hardness of γ-alon. These calculated results provide the basis for understanding the composition-dependent bonding and hardness of γ-alon.
Print ISSN:
0021-8979
Electronic ISSN:
1089-7550
Topics:
Physics
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