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Ferroelectric domain walls are attracting broad attention as atomic-scale switches, diodes, and mobile wires for next-generation nanoelectronics. Charged domain walls in improper ferroelectrics are particularly interesting as they offer multifunctional properties and an inherent stability not found in proper ferroelectrics. Here we study the energetics and structure of charged walls in improper ferroelectric YMnO3,InMnO3, and YGaO3 by first-principles calculations and phenomenological modeling. Positively and negatively charged walls are asymmetric in terms of local structure and width. The wall width scales with the amplitude of the primary structural order parameter and the coupling strength to the polarization, reflecting that polarization is not the driving force for domain formation. We introduce general rules for how to engineer n- and p-type domain wall conductivity based on the domain size, polarization, and electronic band gap. This opens the possibility of fine tuning the local transport properties and designing p-n-junctions for domain wall-based nanocircuitry.

The hydrothermal synthesis of hexagonal YMnO3 and YbMnO3 are reported using high KOH mineraliser concentrations (>10 M) and low temperatures (<240 °C). The relation between reaction parameters and resulting phase purity were mapped by ex situ and in situ X-ray diffraction. Excess Y2O3 resulted in two-phase product with hexagonal YMnO3 with different lattice parameters. An unusual microstructure was observed in which particles have a hexagonal shape with a highly crystalline edge and either a hollow or polycrystalline interior. An Ostwald ripening mechanism was proposed to explain this phenomenon. Solid-state reactions and density functional theory calculations were performed to determine plausible defect chemistry which can lead to the observed phases with different lattice parameters. [ABSTRACT FROM AUTHOR]

A thorough study of the Y1−xZrxMnO3+δ series is presented with the objective to use these materials as SOFC cathodes. These pure and Zr-doped yttrium manganites exhibit a layered hexagonal structure similar to a peculiar 5-fold bipyramidal coordination of manganese that makes them intrinsically different from the traditional cube-like perovskite with [MnO6] octahedra, creating the conditions conducive for oxygen uptake at a low temperature in the case of the layered manganite. Zr for Y doping enables the maintenance of oxygen excess such as interstitial oxygen atoms (Oi) located in the equatorial plane of the bi-pyramids. These over-stoichiometric interstitial oxygen sites are clearly evidenced by the maximum entropy method (MEM) applied to neutron diffraction data, and density functional theory (DFT) calculations are used to model the structural accommodation of Zr and excess oxygen. Mn reduction to Mn2+ is found to be energetically unfavourable, as proved both experimentally and by DFT calculations. Hence, zirconium is found to both stabilize the excess oxygen compared to pure YMnO3 and possibly provide an oxygen ion migration path with a lower energy barrier. The main consequence is a possible MIEC behaviour in Zr-doped YMnO3, as suggested by both the conductivity measurements and theoretical calculations. The initial EIS measurements are very promising and raise the series and its original structure to the rank of materials of interest for application as SOFC electrodes. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) batteries are known as a next-generation energy storage technology due to their high theoretical energy density and low cost. However, the shuttling of soluble lithium polysulfides (LPS) between electrodes hinders the practical realization of Li-S batteries, resulting in short cycle life. To address this issue, this work discloses a highly efficient separator with Fe/Zr binary metal-organic framework (MOF) coated on a polypropylene (PP) separator. Fe3+ metal ions were integrated into the UiO-66(Zr)-NH 2 framework through a simple one-step hydrothermal method. The adsorption test confirmed the superior LPS adsorption capability of the UiO-66(Fe/Zr)-NH 2 than monometallic UiO-66(Zr)-NH 2 , which provides not only uniform-sized nanochannels for effective LPS sorption and even Li+ ions transport but also Fe active sites for electrocatalytic conversion of the LPS. UiO-66(Fe/Zr)-NH 2 -based Li symmetrical cells demonstrated a uniform stripping and plating of Li at exceptionally higher current densities (1–10 mA cm−2). CR2023 coin cell Li-S battery using a S-CNT/GO composite cathode and UiO-66(Fe/Zr)-NH 2 /PP separator delivered an initial discharge capacity of 900 mAh/g at 0.3C and a long cycle life (820 cycles) with minimal capacity decay of merely 0.067 % per cycle. The significantly improved performance demonstrates the potential of binary MOF-based materials for metal-sulfur batteries. [Display omitted] • Fe/Zr binary UiO-66(Fe/Zr)-NH 2 was synthesized to modify Li-S battery separator. • Fe/Zr binary MOF provides nanochannels for LPS sorption and even Li+ ion transport. • Fe sites in MOF promote electrocatalytic conversion to reactivate adsorbed LPS. • An initial discharge capacity of 900 mAh/g at 0.3C in Li-S batteries was achieved. • Long cycle life of 820 cycles and capacity decay 0.067 % per cycle were documented. [ABSTRACT FROM AUTHOR]

The hydrothermal synthesis of hexagonal YMnO3 and YbMnO3 are reported using high KOH mineraliser concentrations (>10 M) and low temperatures (<240 °C). The relation between reaction parameters and resulting phase purity were mapped by ex situ and in situ X-ray diffraction. Excess Y2O3 resulted in two-phase product with hexagonal YMnO3 with different lattice parameters. An unusual microstructure was observed in which particles have a hexagonal shape with a highly crystalline edge and either a hollow or polycrystalline interior. An Ostwald ripening mechanism was proposed to explain this phenomenon. Solid-state reactions and density functional theory calculations were performed to determine plausible defect chemistry which can lead to the observed phases with different lattice parameters.