First-principles calculation on oxygen ion migration in alkaline-earth doped La₂GeO₅

Abstract

By using first-principles calculations based on the density functional theory, we investigated the doping effects of alkaline-earth metals (Ba, Sr and Ca) in monoclinic lanthanum germanate La2GeO5 on its oxygen ion conduction. Although the lattice parameters of the doped systems changed due to the ionic radii mismatch, the crystal structures remained monoclinic. The contribution of each atomic orbital to electronic densities of states was evaluated from the partial densities of states and partial charge densities. It was confirmed that the materials behaved as ionic crystals comprising of cations of La and dopants and anions of oxygen and covalently formed GeO4. The doping effect on the activation barrier for oxygen hopping to the most stable oxygen vacancy site was investigated by the climbing-image nudged elastic band method. By tracing the charge density change during the hopping, it was confirmed that the oxygen motion is governed by covalent interactions. The obtained activation barriers showed excellent quantitative agreements with an experiment for the Ca- and Sr-doped systems in low temperatures as well as the qualitative trend, including the Ba-doped system.

Computational Materials Design of Rare-Earth-Based Fast Oxygen Ion Conductors by First-Principles Simulation Based on Density Functional Theory

“…The interactions between ions and electrons were given by the projector augmented-wave (PAW) method. We employed plane-wave basis sets for describing electronic wave functions with cut-off energies defined for each system (13)(14)(15). The Brillouin zone was sampled with a k-points mesh through the Monkhorst-Pack scheme.…”

“…The Brillouin zone was sampled with a k-points mesh through the Monkhorst-Pack scheme. Geometrical optimizations were performed by minimizing the Hellman-Feynman forces acting on each ion to be less than criteria defined for each system (13)(14)(15). Densities of states were obtained for each optimized geometry by static calculation in which the all atoms and lattice parameters were fixed.…”

“…Figure 3. Potential energy curves of oxygen migration that the vacancy moves from the most stable site to the nearest neighbor GeO 4 tetrahedron for undoped and alkaline-doped lanthanum germanate with the dopant concentration of La 1.8 M 0.2 GeO 4.9 for M = Ca, Sr and Ba (15). The origin of ordinate is defined as the total energy of the initial state.…”

“…Therefore, in spite of the importance, fundamental properties of many of the fast ion conductors are still unknown. However, for the sake of the recent developments in computational technologies, properties of some materials are becoming clarified (13)(14)(15)(16)(17)(18)(19)(20).…”

Self-diffusion mechanisms based defect complexes in MoSi2

“…Although MoSi 2 diffusion experiments provide useful data for the applications of MoSi 2 coating, there is still a lack of quantitative understandings of the microscopic diffusion mechanisms. From the mechanism point of view, the formation and migration of atomic defects are the dominant factors controlling microscopic diffusion behavior [27][28][29][30][31][32][33][34][35][36][37]. There are four kinds of basic point defects in MoSi 2 : Si vacancy (V Si ), Mo vacancy (V Mo ), Si antisite (Si Mo ), Mo antisie (Mo Si ).…”