Ni-Pd

Abstract: A new high-precision angular-dependent potential of the Ni-Pd system was obtained by fitting the experimental data and first-principles calculations. Then, the element segregation characteristics and thermal stability of Ni-Pd bimetallic nanoparticles were investigated by Monte Carlo method and molecular dynamics method. The results show that the chemical ordering pattern of Pd_xNi_1-x nanoparticle is the result of the competition of surface energy, strain energy, bond energy and interface energy. When a small amount of Pd atoms are substitutionally doped into the Ni nanoparticle, all the Pd atoms will be segregated on the surface and dispersed. The synergistic effect of Ni atoms and Pd atoms in the surface will improve the catalytic activity and carbon deposition resistance of Pd_xNi_1-x nanoparticle catalyst in methane dry reforming reaction. Increasing the doping amount of Pd atoms will gradually reduce the melting point of Pd_xNi_1-x nanoparticle, thereby reducing its sintering resistance.

Abstract: Palladium (Pd) has attracted attention as one of the major components of noble metal catalysts due to its excellent reactivity to a wide range of catalytic reactions. It is important to predict and control the atomic arrangement in catalysts because their properties are known to be affected by it. Therefore, to enable atomistic simulations for investigating the atomic scale structural evolution, we have developed interatomic potentials for Pd-M (M = Al, Co, Cu, Fe, Mo, Ni, Ti) binary systems based on the second nearest-neighbor modified embedded-atom method formalism. These potentials reproduce various fundamental properties of the alloys (the structural, elastic and thermodynamic properties of compound and solution phases, and order-disorder transition temperature) in reasonable agreements with experimental data, first-principles calculations and CALPHAD assessments. Herein, we propose that these potentials can be applied to the design of robust bimetallic catalysts by predicting the shape and atomic arrangement of Pd bimetallic nanoparticles.

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 Ni_0.5Fe_0.5, Ni_0.5Co_0.5 and Ni_0.5Pd_0.5 are ordered ferromagnetically, whereas Ni_0.5Cr_0.5 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.