China
Africa
Explore chapters and articles related to this topic
Diffusion and Applications
Published in Zainul Huda, Metallurgy for Physicists and Engineers, 2020
Interstitial Diffusion. Interstitial diffusion involves jumping of atoms from one interstitial site to another without permanently displacing any other atoms in the crystal lattice. Interstitial diffusion occurs when the size of the diffusing (interstitial) atoms are very small as compared to the matrix atoms’ size (see Figure 4.3). For example, in wrought iron, α-ferrite solid solution is formed when small-sized carbon atoms diffuse into BCC lattice of larger-sized iron atoms.
Analytical Physics
Published in Dana Crowe, Alec Feinberg, Design for Reliability, 2017
There are two types of diffusion in solids: interstitial and substitutional, or vacancy. Interstitial diffusion is primarily the diffusion of the light elements hydrogen (H), carbon (C), and nitrogen (N). This is the most rapid type of diffusion because these smaller atoms move between interstitial sites within the lattices since these sites are usually empty. An interstitial site is a space in a lattice between the primary lattice sites.
Dopant Diffusion
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Atomistic models of diffusion in Si are based on the interaction of dopants with point defects in the silicon lattice. There are three native point defects of interest in Si—interstitials, vacancies, and interstitialcies. There exist various mechanisms that allow migration of defects within a lattice, depending on whether the defect is substitutional or interstitial. In interstitial diffusion, the interstitial moves from one interstitial site to an equivalent neighboring site without occupying a lattice site. The interstitial atom could also move by displacing a lattice atom, which, in turn, becomes an interstitial atom. This is an example of the interstitialcy mechanism. A related interstitialcy mechanism is the Crowdion mechanism, in which the interstitial atom located half-way between two lattice sites, migrates to one of the lattice sites and displaces the lattice atom. When a substitutional defect migrates by jumping from its original position to a neighboring vacancy site, the mechanism is called the vacancy mechanism. In general, the migration of any defect from one site to another requires the defect to jump over a barrier Hm. This jump probability is proportional to exp (− Hm/kT).
Structure evolution of vacancy-hydrogen complexes in a nickel-based single-crystal superalloy
Published in Philosophical Magazine Letters, 2022
Xiao-Zhi Tang, Xiao-Tong Li, Ya-Fang Guo
Finally, we examine the MEPs of the decomposition of a complex. For simplicity, in Figure 4, only one hydrogen atom diffuses away and the other hydrogen atoms stay put. Results show that for all three complexes, decompositions at the MDN centre (black dot solid lines) need higher energy than that at the dislocation node (red dot solid lines). The red dot solid lines have humps because the excess volume of the dislocation core allows the diffusing hydrogen atom to stay at a tetrahedron interstitial site during the decomposition. This is a metastable transition state. Regardless of the position of the complex, the MEPs in Figure 4 all indicate that decomposition is not energetically favourable. After decomposition, the system energy rises about 0.5–1.0 eV. This is because other hydrogen atoms are ‘fixed’ at their original sites in the calculation for simplicity. In reality they are expected to find more relaxed positions to release the lattice distortion. So, a decomposition can be witnessed in a structure evolution, just as Figure 2 shows.
First-principles calculations to investigate thermodynamic and mechanical behaviors of molybdenum-lanthanum alloy
Published in Journal of Nuclear Science and Technology, 2023
Lu Wang, Kun Jie Yang, Chenguang Liu, Yue-Lin Liu
We further investigate structural character and thermodynamic stability of La at three positions including tetrahedron interstitial site (TIS), octahedron interstitial site (OIS), and substitution site (SS) in Mo, as shown in Figure. 1(a–c). Figure 2 presents the solution energies of La at these three sites. The solution energies are 10.57 and 11.19 eV for La at TIS and OIS, respectively. Although the solution energy of TIS-La is lower than that of OIS-La, these two energies are relatively higher and endothermic in Mo. So larger solution energies are mainly originated from that both TIS and OIS cannot provide effective space to hold one La atom. In general, the SS should be the preferred position for the alloying element La (as well as other alloying elements) since the SS possesses the larger space compared to these two interstitial sites. As expected, there is indeed a lower solution energy of 2.86 eV for La atom at SS in comparison with both TIS and OIS, as shown in Figure 2. This indicates that the dissolution of La at SS is energetically favorable in Mo. For comparison, three mixed dumbbell structures including <100>, <110> and <111> are also explored, as given in Fig. 1(d–f). One can find that their solution energies are much higher than that of La at SS, as shown in Figure 2. Comparing with each other, the <111> mixed dumbbell is more stable than both <100> and <110> mixed dumbbells, which is in agreement with the previous study [34] that Muzyk et al. calculated the solution energies of W-V and W-Ta mixed dumbbells in W and found that the <111> mixed dumbbell is also the most stable configuration.