Albert M Iskandarov

Effect of cation dopants in zirconia on interfacial properties in nickel/zirconia systems: an atomistic modeling study.

Cation doping is often used to stabilize the cubic or tetragonal phase of zirconia for enhanced thermomechanical and electrochemical properties. In the present paper we report a combined density functional theory (DFT) and molecular dynamics study of the effect of Sc, Y, and Ce dopants on properties of Ni/[Formula: see text] interfaces and nickel sintering. First, we develop an MD model that is based on DFT data for various nickel/zirconia interfaces. Then, we employ the model to simulate Ni nanoparticles coalescing on a zirconia surface. The results show the possibility of particle migration by means of fast sliding over the surface when the work of separation is small (<[Formula: see text]). The sliding observed for the O-terminated Ni(1 1 1)/[Formula: see text](1 1 1) interface is not affected by dopants in zirconia because the work of separation of the doped interface stays small. The most pronounced effect of the dopants is observed for the Zr-terminated Ni(1 1 1)/[Formula: see text](1 1 1) interface, which possesses a large work of separation ([Formula: see text]) and thus restricts the sliding mechanism of Ni nanoparticle migration. DFT calculations for the interface revealed that dopants with a smaller covalent radius result in a larger energy barriers for Ni diffusion. We analyze this effect and discuss how it can be used to suppress nickel sintering by using the dopant selection.

Theoretical shear strength of FCC and HCP metals

The theoretical shear strength (τc) and its temperature dependence for a series of FCC and HCP metals have been calculated. Despite the obtained differences in temperature dependences of τc, critical deformation (γc), and shear modulus (G), the fact of a weak temperature dependence of ratio Gγc/τc relating these quantities is established for all studied materials. The deviation of Gγc/τc from the average value in the temperature ranges under consideration is no more than 12%.

Development of a new dipole model: interatomic potential for yttria-stabilized zirconia for bulk and surface

We developed a new interatomic potential for yttria-stabilized zirconia (YSZ) based on the dipole model initially proposed by Tangney and Scandolo. It is demonstrated that the potential can successfully reproduce not only basic bulk properties, including interaction between point defects, but also energies and structures of clean (1 1 0) and (1 1 1) surfaces. We confirmed that the highly perturbed structure of (1 1 0) surface doped by yttria is in a good agreement with results of DFT calculations. Yttrium segregation at (1 1 1) surface was predicted and discussed by comparison with results of DFT simulations.

Strength of silicon nanolayers under tensile loading

Tensile strength of silicon slabs is estimated by means of classical molecular dynamics simulation. Effects of temperature and surface defects, namely vacancies and linear steps, on the strength are examined. It is found that the presence of vacancies on the slab’s surface decreases the critical strain, whereas the change of their concentration does not cause its significant changes. In contrast, increasing the temperature and surface step height gradually decreases the critical strain.

Atomistic Model Analysis of Local and Global Instabilities in Crystals at Finite Temperature

There have been a lot of studies dedicated to structural instability in solids. For local instability, theoretical (ideal) strength of crystals has been extensively studied with ab initio calculations. Global instability taking into account the collective motion of atoms involved in deformation has also been investigated. However, these studies have usually been done at 0 K and little has been understood about the effect of temperature. In this study, we demonstrate computational approaches to the effect of temperature on local and global instabilities. Ideal shear strength (ISS) of silicon at finite temperatures is calculated by molecular dynamics (MD) simulations with an empirical potential. ISS is obtained as a function of temperature. Our results imply that, unlike metals, the reduction in ISS by temperature cannot be estimated simply by taking into account thermal expansion of volume. In addition, global instability for dislocation nucleation in a Cu thin film model under tension is investigated. We first evaluated instability modes at 0 K with increasing strain, and then performed MD simulations at 50 K. After the nucleation of a partial dislocation, the second dislocation can be one to create a twin or one to create another partial dislocation. These different deformations can be understood as the competition of latent instability modes that have relatively small eigenvalues.