Stabilizing spinel structures with Zn preferring a tetrahedral environment significantly improves the reversibility of the spinel–rocksalt transition with Mg insertion/extraction.

Li x La (1−x)/3 NbO 3 is an A-site-deficient perovskite material that exhibits structure-dependent ionic conductivity. La 1/3 NbO 3 has a larger unit cell volume, lower concentration of La 3+ ions, and higher concentration of intrinsic vacancies than La 2/3 TiO 3 . As such, it should exhibit higher Li ion conductivity and, therefore, be a good candidate for all ceramic Li secondary batteries or fast Li ion transport solid-state electrolyte batteries. However, experimental observations show otherwise. Information on the local atomic arrangements would facilitate the analysis of the gap between the theoretical and experimental results. Ab initio density functional theory calculations are useful for calculating the atomic arrangements and energies. However, because of cell size limitations, long-range ordering in La/Li/vacancy arrangements cannot be observed using ab initio calculations. In this study, cluster expansion and Monte Carlo simulations were utilized to bridge this gap. The computational results reproduce the stacking of alternate La-rich and La-poor layers along the c-axis, consistent with the experimental data. In addition, two possible modulated structures for the La-rich layers were discovered. These should help explain the lower-than-expected ionic conductivity and the possible Li ion migration pathways in the material. Based on the presented Monte Carlo simulations, we conclude that the two types of low-energy structures, the closed and striped arrangements, may coexist in the real system. The modulated structures in experimental studies are likely to be numberless nanodomains composed of these two arrangements. If the majority of the structure shows a closed arrangement at room temperature, most of the Li ions will be trapped at the center of the periodic units in the closed arrangement. This could explain the lower-than-expected Li ion conductivity in Li x La (1−x)/3 NbO 3 .

Barium titanate is the dielectric material of choice in most multilayer ceramic capacitors (MLCCs) and thus in the production of ≈3 trillion devices every year, with an estimated global market of ≈$8330 million per year. Rare earth dopants are regularly used to reduce leakage currents and improve the MLCC lifetime. Simulations are used to investigate the ability of yttrium, dysprosium, and gadolinium to reduce leakage currents by trapping mobile oxygen defects. All the rare earths investigated trap oxygen vacancies, however, dopant pairs are more effective traps than isolated dopants. The number of trapping sites increases with the ion size of the dopant, suggesting that gadolinium should be more effective than dysprosium, which contradicts experimental data. Additional simulations on diffusion of rare earths through the lattice during sintering show that dysprosium diffuses significantly faster than the other rare earths considered. As a consequence, its greater ability to reduce oxygen migration is a combination of thermodynamics (a strong ability to trap oxygen vacancies) and kinetics (sufficient distribution of the rare earth in the lattice to intercept the migrating defects).the high activation barriers make events too infrequent for reliable statistics in molecular dynamics. Methods exist which compel the simulation to investigate the high-energy configurations involved in such processes. Metadynamics [1] is a powerful example of this approach that has enabled studies of crystallization, [2] phase transformations, [3] protein interactions, [4] and molecular docking processes [5,6] and recently diffusion processes, [7] providing new insight at the atomic level into complex physics and chemistry. We use it here to investigate how rare earth (RE) dopants in barium titanate (BaTiO 3 ) trap mobile oxygen defects to prevent capacitor breakdown and improve the lifetime of multilayer ceramic capacitors (MLCCs).BaTiO 3 is a ferroelectric perovskite used in many electronic devices. It has a high relative permittivity at room temperature so that high capacitances can be achieved with thin layers in capacitor applications. [8] It is the dielectric used in MLCCs and thus in the production of ≈3 trillion devices every year with an estimated global market of ≈$8.4 B in 2016. [9] The failure of these capacitors [10] is usually ascribed to the diffusion of oxygen ions, which produces a leakage current. As a consequence, BaTiO 3 is frequently doped with RE 3+ ions to trap the mobile oxygen defects and so improve its electrical properties for MLCC applications. [11] The incorporation of these ions affects the microstructure of the ceramic, producing core-shell grain structures that improve the temperature dependence of capacitance for MLCCs [12] as well as their electrical stability. Doping with mid-size (0.9-0.94 Å [13] ) RE 3+ ions (particularly Dy 3+ ) [11,[14][15][16] leads to improved lifetimes for MLCCs.Undoped bulk ceramic BaTiO 3 contains a low concentration of intrinsic oxygen vacancies from the Schottky mechanism [1...

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A new computational analysis of tilt behaviour in perovskites is presented. This includes the development of a computational program – PALAMEDES – to extract tilt angles and the tilt phase from molecular dynamics simulations. The results are used to generate simulated selected-area electron and neutron diffraction patterns which are compared with experimental patterns for CaTiO3. The simulations not only reproduced all symmetrically allowed superlattice reflections associated with tilt but also showed local correlations that give rise to symmetrically forbidden reflections and the kinematic origin of diffuse scattering.