Electron–phonon coupling in Ni-based binary alloys with application to displacement cascade modeling

Abstract

Energy transfer between lattice atoms and electrons is an important channel of energy dissipation during displacement cascade evolution in irradiated materials. On the assumption of small atomic displacements, the intensity of this transfer is controlled by the strength of electron-phonon (el-ph) coupling. The el-ph coupling in concentrated Ni-based alloys was calculated using electronic structure results obtained within the coherent potential approximation. It was found that Ni0.5Fe0.5, Ni0.5Co0.5 and Ni0.5Pd0.5 are ordered ferromagnetically, whereas Ni0.5Cr0.5 is nonmagnetic. Since the magnetism in these alloys has a Stoner-type origin, the magnetic ordering is accompanied by a decrease of electronic density of states at the Fermi level, which in turn reduces the el-ph coupling. Thus, the el-ph coupling values for all alloys are approximately 50% smaller in the magnetic state than for the same alloy in a nonmagnetic state. As the temperature increases, the calculated coupling initially increases. After passing the Curie temperature, the coupling decreases. The rate of decrease is controlled by the shape of the density of states above the Fermi level. Introducing a two-temperature model based on these parameters in 10 keV molecular dynamics cascade simulation increases defect production by 10-20% in the alloys under consideration.

Electron-phonon interaction within classical molecular dynamics

“…The value obtained, λ = 0.24, is very close to 0.26, obtained previously 3,21 using a rigid muffin-tin potential approach (RMTA)…”

Two-temperature model in molecular dynamics simulations of cascades in Ni-based alloys

“…The friction coefficient corresponding to the electronic stopping was calculated using SRIM tables [26], and is equal to 0.6 ps for all systems. The e-ph coupling parameters g p used in the 2T-MD cascades were calculated at 300 K, using the rigid muffin-tin approximation (RMTA) of Gaspari and Gyorffy [27], with the use of electronic structure results within the coherent potential approximations [28] (CPA) [29], and have values of 8.48×10 17 W m −3 K −1 for NiFe, 6.81×10 17 W m −3 K −1 for NiCr, and 11.2×10 17 W m −3 K −1 for NiFeCr. Earlier [30], the good agreement between e-ph coupling values obtained by time dependent density functional theory (TD-DFT [31]) and RMTA was demonstrated for the case of pure Ni.…”

“…For the electronic grid, which consists of 32 × 32 × 32 cells, Robin The calculated DOS for the NiFeCr alloy is presented in (Fig. 1), while the DOS for the binary alloys can be found in [29]. The electronic states at the Fermi energy (zero energy in Fig.…”

The effect of alloying nickel with iron on the supersonic ballistic stage of high energy displacement cascades

“…Depending on thermal conductivities, temperatures at the center of the subcascade cores remain over 1000 K for a few ps to more than 10 ps. This can be especially long in concentrated alloys, where lattice and electronic thermal conductivities can be quite low [4,2,15,26]. At these elevated temperatures, coarsening and annihilation of defects and defect precursors is quite important.…”