1 O mechanism Starting from the O state as shown in figure 6 there are mainly

1 o mechanism starting from the o state as shown in

This preview shows page 9 - 11 out of 17 pages.

1. O-mechanism Starting from the O state (as shown in figure  6 ), there are mainly three migration pathways. (1.a) Direct O-O hopping . As shown in figure  7 below, the O state SIA directly migrates to the 1st and 2nd nearest neighbor (NN) O states, with the migration barriers of 0.028 eV and 0.062 eV, respectively. (1.b) O-M1-BC migration. As shown in figure  8 below, the SIA in the O state first moves away from the middle plane and evolves to a middle state M1, where the extra atom stays slightly above the basal plane. Then the SIA moves further downward to the basal plane and forms the BC state. Although figure  8 shows only one pathway of O-M1-BC, the O-M1 transition actually has a degen- eracy of two, i.e. the SIA can move either upward or downward, and eventually leads to two BC states on different basal planes. The associated migration barriers are also marked in the figure. The effective barrier from O state to BC state is about 0.13 eV, while the effective barrier from BC state to O state is around 0.04 eV. It can be seen that M1 is quite unstable due to the small transi- tion barriers to either O or BC state. (1.c) O-M2-O migration . The O-M2-O migration is an inter- stitialcy mechanism. As shown in figure  9 below, the extra atom in O state first moves away from the middle plane and forms a dumbbell (M2) with the nearest atom in the basal plane. (This M2 is actually the split configu- ration [ 49 , 52 ].) Then the nearest atom is pushed to an O state in another unit cell. The degeneracy for the O-M2 transition is two since there are two nearest-neighbor atoms to the SIA. The corresponding migration barriers are also marked in the figure. The effective barrier for this interstitialcy mechanism is around 0.1 eV. It can also be seen that M2 is an unstable state due to the very shallow minimum. 2. BC mechanism Starting from the BC state (as shown in figure  6 ), we observe three migration pathways. (2.a) BC-BC glide motion . Since BC is in crowdion structure, it easily glides with a low migration barrier 0.013 eV. The 1D glide motion has a degeneracy of two. Table 1. The formation energy of the SIA states in hcp Zr, and the comparison against previously reported results using the same MA07 potential. SIA state Current study (eV) Mendelev et al [ 40 ] (eV) Khater et al [ 53 ] (eV) O 2.74 2.88 2.78 BO 2.86 2.90 N/A BC 2.83 2.91 N/A Figure 6. Only three stable SIA sites, O, BC, and BO, are found to be stable in hcp Zr, among all the six possible geometric sites surveyed using the MA07 interatomic potential. J. Phys.: Condens. Matter 26 ( 2014 ) 365402
Image of page 9

Subscribe to view the full document.

Y Fan et al 9 (2.b) BC-M1-O migration . The mechanism is just the reverse pathway of O-M1-BC, with a barrier or about 0.04 eV. The configurations and barriers are shown above in figure  8 . Notice that the BC-M1 transition has the degen- eracy of two, since the middle atom in the crowdion can move either upward or downward.
Image of page 10
Image of page 11
  • Summer '19
  • Transition state, KMC

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes