The mechanism of ionic conductivity in stabilized cubic zirconia

The electron-density functional method (in the gradient approximation) and the pseudopotential method are used to study the mechanism of ionic conductivity in the cubic phase of zirconia stabilized with magnesium or yttrium. The oxygen-ion migration in the stabilized zirconia is shown to be a two-stage process, which consists in the formation of active oxygen vacancies and in oxygen-ion jumps from one active vacancy to another. The total activation energy of these processes is calculated to be 1.0–1.5 eV, which agrees with experimental data.     

On the Calculation of the Interaction Potential in Multiatomic Systems

Computational Mathematics and Mathematical Physics - A numerical method for finding the potential of a multiatomic system in the real space is proposed. A distinctive feature of this method is the...     

Stability of cubic zirconia and of stoichiometric zirconia nanoparticles

Using the electron density functional method, it is shown that the oxygen sublattice of cubic zirconia is unstable with respect to random displacements of oxygen atoms, which results in general instability of bulk cubic zirconia at low temperatures. A comparison of the equilibrium atomic structures and total energies of stoichiometric ZrO₂ nanoparticles about 1 nm in size shows that particles with cubic symmetry are more stable than those with rhombic (close-to-tetragonal) symmetry. The electronic structure of nanoparticles exhibits an energy gap at the Fermi level; however, this gap (depending on the symmetry and size of the particle) can be much narrower than the energy gap of the bulk material.     

Quantum-mechanical modeling without wave functions

It has been shown that the variational principle can be used as the practical way to find the electron density and the total energy in terms of the density functional theory without solving the Kohn-Sham equations (the so-called orbital-free approach). The equilibrium interatomic distances and binding energies found using examples of diatomic systems Si₂, Al₂, and P₂ are in good agreement with the published data. The results obtained for Si-Al, Si-P, and Al-P dimers are also close to the results obtained by the Kohn-Sham method.     

Electronic States of Nanostructured Systems: Titanium and Zirconia

The density functional method with pseudopotentials are used to study the electron states of nanoparticles and nanostructured systems: chains, films, and three-dimensional nanosystems of titanium and zirconia. It is shown that all studied titanium nanosystems have the density of electronic states (DES) of the metallic type, but zirconia nanosystem demonstrates a dielectric energy gap in the vicinity of the Fermi level. The density of states of nanostructured titanium is close in shape to DES of the single crystal but has a smoother shape due to disordering of the atomic arrangement. The forbidden band width of the nanostructured zirconia is smaller as compared to the corresponding width in crystalline ZrO₂, supposedly because of incomplete saturation of ionic bonds.     

Influence of impurities on the stability and electronic states of titanium dioxide in the form of anatase

The behavior of impurities (Si, Zr, Mg, Zn) in titanium dioxide with an anatase structure is investigated using the electron-density functional method (with due regard for the spin polarization). The influence of these impurities on the formation of oxygen vacancies and the specific features of the electronic structure is studied. It is demonstrated that the impurities can both improve and deteriorate the optical characteristics of titanium dioxide.     

Computer study of boron and phosphorus at the Si(100)̶2 ╳ 1 surface

The AM1 semiempirical numerical method combined with the geometry optimization procedure was used to study the energetics of active impurities (B, P) in substitutional positions at the Si(100)- surface. It has been found that phosphorus prefers to be in the first layer (in dimers). Boron has the lowest energy in the second layer. Energy profits, counting from the fourth bulk-like layer, for B and P are 1.33 eV and 0.56 eV, respectively. Comparing of the P-Si and P-P dimers energetics has shown that P-Si dimers are more preferable energetically. Received: 26 March 1998 / Accepted: 9 June 1998     

Growth of tungsten whiskers oriented in <111> direction

The electron micro diffraction technique and pseudopotential ab initio calculations were implemented to study in details the formation and mechanism of growth of the tungsten whiskers during the reduction of nickel tungstate by CO gas. It has been shown that the W whiskers prefer to grow as crystals oriented in the <111> direction, and this process may be considered as the epitaxial growth on the hexagonal planes of Ni₄W particles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)