Diffusion mechanism of bound Schottky defect in magnesium oxide

Abstract

In simple ionic crystals, intrinsic point defects must satisfy electrical neutrality and exist as Schottky defects. In magnesium oxide (MgO), a Schottky defect is then a combination of anionic and cationic vacancies. Since vacancies are charged, the stable configuration of the Schottky defect corresponds to a bound pair of vacancies of opposite signs. In this study, we investigate the kinetics of formation and migration of such a bound pair on long timescales reaching in some cases thousands of seconds using the kinetic activation-relaxation technique, an off-lattice kinetic Monte Carlo method with an event catalog built on-the-fly during static molecular simulations. We show that the diffusion of this bound Schottky defect involves the migration of vacancies bounded to the first and third neighbor sites of the crystal structure with an apparent migration energy which cannot be inferred from the migration energies expected from isolated defects. Overall, this study gives insights and constraints on the oxygen diffusion mechanism reported experimentally in high-purity MgO samples.

CO adsorption on MgO thin-films: formation and interaction of surface charged defects

“…35 However, although experimentally defects are obtained under strain relaxation or even after preparation in a pure oxygen ambient atmosphere, 5 theoretical insights are essentials to elucidate the influence of charged defects at MgO films. 36,37…”

“…35 However, although experimentally defects are obtained under strain relaxation or even after preparation in a pure oxygen ambient atmosphere, 5 theoretical insights are essentials to elucidate the influence of charged defects at MgO films. 36,37 Electron paramagnetic resonance (EPR) shows that paramagnetic centers formed during the electron transfer process under molecular reaction conditions are preferably found at step edges and thicker MgO films. 38,39 However, the identification of non-paramagnetic centers at surface sites of oxide materials is less straightforward.…”

“…17,19,27 Accordingly, the experimentally measured shift of the work function may be substantially affected by the position, charge state and density of defects in the MgO thin-film, thereby leading to strong local potential shifts associated with electron acceptor and donor centers. 13,32 From the simulation of defects and trapped electrons at the MgO surface, 20,37,[47][48][49][50] the knowledge of the electronic structure of charged intrinsic vacancies at thin-films may gather further insights on interfaces and 2D materials with catalytic potential.…”

A Novel Interstitial Site in Binary Rock-Salt Compounds

“…Unfortunately, only tetrahedral sites have been considered for interstitial defects, leaving split interstitials unexplored. In addition, several theoretical studies [ 25 , 38 , 39 ] have been conducted on the intrinsic defects in alkaline-earth metal monochalcogenides (groups II–VI). In particular, Huang [ 25 ] performed a theoretical study on native defects in CaS and considered the tetrahedral site for the interstitial defect.…”

Free Energy Surfaces and Barriers for Vacancy Diffusion on Al(100), Al(110), Al(111) Reconstructed Surfaces

“…Al is of particular interest recently due to its exceptional properties [ 34 , 35 , 36 , 37 , 38 , 39 ]. On the other hand, defects like vacancy are omnipresent on crystals and play an important role in their properties [ 40 , 41 , 42 , 43 , 44 ]. Substantial experimental and theoretical efforts have been employed over many years to elucidate the free energy surfaces and free energy barriers of diffusion on crystal surfaces [ 45 , 46 , 47 , 48 ].…”