Computational study of oxynitride based strong materials
Date
2010-04-16T08:10:05Z
Authors
Okeke, Onyekwelu Uzodinma
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Abstract
A spinel oxynitride material in the form M3NO3 (M = B, Al, Ga, or In) is considered to be
derived from a reaction of the formMN +M2O3!M3NO3. Various possible phases ofMN
and M2O3 that could lead to M3NO3 oxynitride spinel material have been considered in the
work. The structural, electronic, elastic properties and the relative stabilities of the bulk and
the nature of the resulting vacancies or defect-related properties of these oxynitride spinel
structures are investigated using ab-initio or first principles electronic structure methods
based on density functional theory (DFT). The bulk oxynitride spinel structure containing
B and Al atoms exhibit higher resistance to compression and shear than those containing Ga
and In atoms and therefore, these are suggested to be potentially important hard materials
possibly formed under extreme conditions. Calculated energetics of the proposed reaction
favor the formation of oxynitride spinels containing Ga and In with such materials having
potentially significant optoelectronic applications. From results on defective oxynitride
systems, with a vacancy at octahedral or tetrahedral sites, it is suggested that the structural
stability of the oxynitride spinel materials could be lowered.
In this thesis, a series of Tersoff empirical potentials for the bulk oxynitride spinel systems
is proposed and tested by calculating the structural and elastic properties of the binary
nitrides and M3NO3 oxynitride spinels using molecular dynamics simulation. The apparent
success of treating some binary nitride systems using the Tersoff potential is used as a way
forward to obtain a new parameter set that incorporates atomic features into a series of Tersoff
potential for ternary oxynitrides spinel phases. The different thermodynamic properties
of these oxynitride structure for varying temperature are also predicted such as the Debye
temperature, thermal expansion co-efficient and specific heat. It is suggested that these
materials will have thermal properties comparable to their binary nitride counterparts.