The effect of defect interactions on the reduction of doped ceria.

Doped cerium oxide is known for its reduction properties that are utilized in catalytic applications as well as in thermochemical cycling to produce solar fuels. Upon reduction of the lattice, oxygen vacancies and polarons are formed leading to a highly concentrated solution of defects in which the interactions of defects cannot be neglected anymore. In this study, the effect of defect interactions on the free energy of reduction for doped ceria with composition Ce1-x-yRExZryO2-x/2-δ was investigated by large scale Metropolis Monte Carlo multi-stage sampling simulations based on first-principles calculations.

The effect of ionic defect interactions on the hydration of yttrium-doped barium zirconate.

Hydrated acceptor-doped barium zirconate is a well-investigated proton conductor. In the analysis of most experimental studies, an ideal defect model is applied to fit the measured hydration data and obtain corresponding enthalpies and entropies. However, the data show a distinct deviation from ideal behaviour and thus defect interactions cannot be neglected.

MOCASSIN: Metropolis and kinetic Monte Carlo for solid electrolytes.

The combination of density functional theory and Monte Carlo simulations is a powerful approach for the atomistic modeling of defect transport in solid electrolytes. The present contribution introduces the MOCASSIN software (Monte Carlo for Solid State Ionics) for kinetic and Metropolis Monte Carlo simulations of crystalline materials. MOCASSIN combines model building, visualization, and simulation, aiming to provide accessible MC for end users.

Publisher Correction: Nanoscale percolation in doped BaZrO for high proton mobility.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Nanoscale percolation in doped BaZrO for high proton mobility.

Acceptor-doped barium zirconate is a promising proton-conducting oxide for various applications, for example, electrolysers, fuel cells or methane-conversion cells. Despite many experimental and theoretical investigations there is, however, only a limited understanding as to how to connect the complex microscopic proton motion and the macroscopic proton conductivity for the full range of acceptor levels, from diluted acceptors to concentrated solid solutions. Here we show that a combination of density functional theory calculations and kinetic Monte Carlo simulations enables this connection.

Defect formation and migration in Nasicon LiAlTi(PO).

NASICON-structured materials of the composition LiAlTi(PO) are regarded as solid electrolytes with high Li-ion conductivity applicable in all solid-state batteries. In this study we investigate the migration paths of constituting ions and monovalent charge carriers including K, Na, and, H. The results proof that Li is the most mobile species in the investigated composition and that the formation of intrinsic defects is unlikely.

Influence of the lattice constant on defects in cerium oxide.

The lattice constant has a crucial effect on the defect chemistry and defect kinetics in solid state materials. However, within density functional theory, some functionals perform badly in reproducing the experimental lattice constant. In this study, energies of defect formation, interaction and migration in the model system ceria were calculated for different lattice constants to investigate the impact on the energies.

Understanding the ionic conductivity maximum in doped ceria: trapping and blocking.

Materials with high oxygen ion conductivity and low electronic conductivity are required for electrolytes in solid oxide fuel cells (SOFC) and high-temperature electrolysis (SOEC). A potential candidate for the electrolytes, which separate oxidation and reduction processes, is rare-earth doped ceria. The prediction of the ionic conductivity of the electrolytes and a better understanding of the underlying atomistic mechanisms provide an important contribution to the future of sustainable and efficient energy conversion and storage.

Entropies of defect association in ceria from first principles.

Defects and their interactions play a crucial role for the properties of solid state materials. While energies of defect formation and defect interaction are commonly calculated from first principles, calculations of corresponding vibrational entropies in solids are less common due to the high computational demand. This is in particular true for defect pairs as the existence of multiple defects lowers the symmetry of the cell.

Ab initio calculation of the attempt frequency of oxygen diffusion in pure and samarium doped ceria.

The rate of oxygen ion jumps in a solid oxide depends not only on the activation energy but also on the pre-exponential factor of diffusion. In order to allow a fully ab initio prediction of the oxygen ion conductivity in pure and samarium doped ceria, we calculated the attempt frequency for an oxygen ion jump from first principles combining DFT+U, the NEB method, phonon calculations and the transition state theory. Different definitions of the jump attempt frequency are presented.

Association of defects in doped non-stoichiometric ceria from first principles.

We investigate the interaction and distribution of defects in doped non-stoichometric ceria Ce1-xRExO2-x/2-δ (with RE = Lu, Y, Gd, Sm, Nd, and La) by combining DFT+U calculations and Monte Carlo simulations. The concentrated solution of defects in ceria is described by the pair interactions of dopant ions, oxygen vacancies, and small polarons. The calculated interaction energies for polarons and oxygen vacancies are in agreement with experimental results and previously reported calculations.

A combined DFT + U and Monte Carlo study on rare earth doped ceria.

We investigate the dopant distribution and its influence on the oxygen ion conductivity of ceria doped with rare earth oxides by combining density functional theory and Monte Carlo simulations. We calculate the association energies of dopant pairs, oxygen vacancy pairs and between dopant ions and oxygen vacancies by means of DFT + U including finite size corrections. The cation coordination numbers from ensuing Metropolis Monte Carlo simulations show remarkable agreement with experimental data.

Entropies of defect formation in ceria from first principles.

We calculate entropies of formation for fully charged point defects, including the small polaron Ce'(Ce), in undoped fluorite-structured ceria by means of density functional theory in the GGA + U approximation. We discuss the behaviour of the entropy for the constant volume and the constant pressure case. Our results for constant pressure (p = 0) suggest that the change in volume, due to the formation of defects, dominates the entropy of formation.

Optical illusion alters M1 excitability after mirror therapy: a TMS study.

The contralesional primary motor cortex (M1) has been suggested to be involved in the motor recovery after mirror therapy, but whether the ipsilesional M1 is influenced by the contralesional M1 via transcallosal interhemispheric inhibition (IHI) is still unclear. The present study investigated the change of IHI as well as the intracortical inhibition and intracortical facilitation of both M1 induced by training in a mirror with the use of transcranial magnetic stimulation (TMS). In this 2 × 2 factorial design (time × group), healthy subjects exercised standardized motor skills with their right hand on four consecutive days.

Association of activity changes in the primary sensory cortex with successful motor rehabilitation of the hand following stroke.

Background: Previous studies demonstrated a posterior shift of activation toward the primary sensory cortex (S1) following stroke; however, any relationship between this posterior shift and clinical outcome measures for the affected hand function were unclear.

Objective: The authors investigated the possible role of S1 in motor recovery.

Methods: Assuming that previous studies examined inhomogeneous groups of patients, the authors selected participants with chronic stroke who had moderate hand paresis, normal sensory examination and somatosensory-evoked potentials, and no lesion within the S1, thalamus, or brain stem.

Long-term mortality and risk of stroke after transient ischemic attack: a hospital-based cohort study.

Background: Stroke and mortality rates in patients with transient ischemic attack (TIA) differ widely between community-based studies and research cohorts. Our aim therefore was to provide a reliable estimate for TIA patients treated in German neurology departments with an acute stroke unit.

Methods: A total of 1951 consecutively admitted TIA patients were prospectively documented in 13 centers and 1480 (75.

[Rate of restenosis after coronary stent implantation depending on regional left ventricular function].

At present the rate of restenosis after PTCA and stent implantation is approximately 30% in clinical routine practice. The aim of the present study was to investigate the influence of regional disturbances of left ventricular contractility, e.g.