Zhang, Z., Jin, H., Pan, J., Chai, J., Wong, L. M., Sullivan, M. B., & Wang, S. J. (2015). Origin of Al Deficient Ti2AlN and Pathways of Vacancy-Assisted Diffusion. The Journal of Physical Chemistry C, 119(29), 16606–16613. https://doi.org/10.1021/acs.jpcc.5b03249
To understand the origin of the Al deficient Ti2AlN MAX phase observed in our experiments, the formation and the diffusion pathway of Al vacancy in Ti2AlN have been calculated by density functional theory (DFT). Compared to Ti and N vacancies, Al vacancies require the lowest formation energies not only in the bulk but also at the top surface layer and the second surface layer. As a result, Ti2AlN is calculated to be capable of accommodating Al vacancies in the supercell down to a substoichiometric Ti2Al0.75N while maintaining the MAX phase structure. After the vacancy formation, Al atom is calculated to diffuse along the (0001) plane preferentially via vacancy jump with an energy barrier of 0.80 eV, leading to Al surface segregation and subsequent desorption from Ti2AlN at high temperatures.
This research / project is supported by the A*STAR, Science and Engineering Research Council (SERC) - Aerospace Program
Grant Reference no. : Grant 112 155 0512