A Stabilization Mechanism of Zirconia Based on Oxygen Vacancies Only

The effects of high concentration of point defects in crystalline ZrSiO4 as originated by exposure to radiation, have been simulated using first principles density functional calculations. Structural relaxation and vibrational studies were performed for a catalogue of intrinsic point defects, with different charge states and concentrations. The experimental evidence of a large anisotropic volume swelling in natural and artificially irradiated samples is used to select the sub...

Structural, mechanical, electronic, and thermodynamic properties of fluorite and tetragonal phases of ZrH$_{2}$ are systematically studied by employing the density functional theory within generalized gradient approximation. The existence of the bistable structure for ZrH$_{2}$ is mainly due to the tetragonal distortions. And our calculated lattice constants for the stable face-centered tetragonal (fct) phase with \emph{c/a}=0.885 are consistent well with experiments. Through...

We propose an approach to calculate the anharmonic part of the volumetric-strain and temperature dependent free energy of a crystal. The method strikes an effective balance between accuracy and computational efficiency, showing a $\times10$ speed-up on comparable free energy approaches at the level of density functional theory, with average errors less than 1 meV/atom. As a demonstration we make new predictions on the thermodynamics of substoichiometric ZrC$_x$, including vac...

The study of zinc oxide, within the homogeneous electron gas approximation, results in overhybridization of zinc $3d$ shell with oxygen $2p$ shell, a problem shown for most transition metal chalcogenides. This problem can be partially overcome by using LDA+$U$ (or, GGA+$U$) methodology. However, in contrast to the zinc $3d$ orbital, Hubbard type correction is typically excluded for the oxygen $2p$ orbital. In this work, we provide results of electronic structure calculations ...

First principles based phase diagram calculations were performed for the octahedral-interstitial solid solution system \alpha ZrOX (\alpha Zr[ ]_(1-X)OX; [ ]=Vacancy; 0 \leq X \leq 1/2). The cluster expansion method was used to do a ground state analysis, and to calculate the phase diagram. The predicted diagram has four ordered ground-states in the range 0 \leq X \leq 1/2, but one of these, at X=5/12, is predicted to disproportionate at T \approx 20K, well below the experime...

The paper presents the first-principle calculation of the electron-phonon coupling and the temperature dependence of the intrinsic electrical resistivity of the zirconium-hydrogen system with various hydrogen concentrations. The nature of the anomalous decrease in the electrical resistivity of the Zr-H system with the increase of hydrogen concentration (at the high concentrations of H/Zr$>$1.5) was studied. It was found that the hydrogen concentration, where the resistivity s...

Hydrogen embrittlement in zirconium alloys is one of current challenges of nuclear reactor containment and can lead to a rapid decrease in mechanical properties of materials. Although many previous studies investigated the mechanism of hydrogen embrittlement at high hydrogen concentration, few studies concentrate on the mechanism at low hydrogen concentration which is before the formation of hydrides (only in the hydrogen complex state). The purpose of this study is to illumi...

We have studied zirconia films on a Rh(111) substrate with thicknesses in the range of 2-10 monolayers (ML) using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Zirconia was deposited using a UHV-compatible sputter source, resulting in layer-by-layer growth and good uniformity of the films. For thicknesses of 2-4 ML, a layer-dependent influence of the substrate on the structure of the thin films is observed. Beyond this thickness, films show a...

Using the first-principles density-functional theory plan-wave pseudopotential method, we investigate the structure and magnetism in 25% Mn substitutive and interstitial doped monoclinic, tetragonal and cubic ZrO2 systematically. Our studies show that the introduction of Mn impurities into ZrO2 not only stabilizes the high temperature phase, but also endows ZrO2 with magnetism. Based on the simple crystal field theory (CFT), we discuss the origination of magnetism in Mn doped...

With density functional theory we have performed molecular dynamics simulations of ZrC which displayed spontaneous Frenkel pair formation at a temperature of 3200 K, some 500 K below the melting point. To understand this behaviour, rarely seen in equilibrium simulations, we quenched and examined a set of lattices containing a Frenkel pair. Five metastable structures were found, and their formation energies and electronic properties were studied. Their thermal generation was f...