Origin of Al Deficient Ti2AlN and Pathways of Vacancy-Assisted Diffusion

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• 作者：Zheng Zhang ; Hongmei Jin ; Jisheng Pan ; Jianwei Chai ; Lai Mun Wong ; Michael B. Sullivan ; Shi Jie Wang
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 23, 2015
• 年：2015
• 卷：119
• 期：29
• 页码：16606-16613
• 全文大小：488K
• ISSN：1932-7455

文摘

To understand the origin of the Al deficient Tib>2b>AlN MAX phase observed in our experiments, the formation and the diffusion pathway of Al vacancy in Tib>2b>AlN 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, Tib>2b>AlN is calculated to be capable of accommodating Al vacancies in the supercell down to a substoichiometric Tib>2b>Alb>0.75b>N 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 Tib>2b>AlN at high temperatures.