Synthesis and crystal chemistry of the NaMSO4F family (M = Mg, Fe, Co, Cu, Zn)

Our work in metal fluorosulphate chemistry, which was triggered by the discovery of the tavorite-phase of LiFeSO₄F, has unveiled many novel Li- and Na-based phases with desirable electrochemical and/or transport properties. Further exploring this rich crystal chemistry, we have synthesized the Na-based magnesium, copper and zinc fluorosulphates, which crystallise in the maxwellite (tavorite-like framework) structure just as their Fe and Co counterparts, which were previously reported. These phases show ionic conductivities in the range of ∼10⁻⁷ S cm⁻¹ or ∼10⁻¹¹ S cm⁻¹ depending upon their synthesis process and no reversible electrochemical activity versus Na.     

Enabling the Li-ion conductivity of Li-metal fluorosulphates by ionic liquid grafting

Recently unveiled ‘alkali metal fluorosulphate (AMSO₄F)’ class of compounds offers promising electrochemical and transport properties. Registering conductivity value as high as 10⁻⁷ S cm⁻¹ in NaMSO₄F phases, we explored the fluorosulphate group to design novel compounds with high Li-ion conductivity suitable for solid electrolyte applications. In the process, we produced sillimanite-structured LiZnSO₄F by low temperature synthesis (T ≤ 300 °C). Examining this phase, we accidentally discovered the possibility of improving the ionic conductivity of poor conductors by forming a monolayer of ionic liquid at their particle surface. This phenomenon was studied by solid-state NMR, XPS and AC impedance spectroscopy techniques. Further, similar trends were noticed in other fluorosulphate materials like tavorite LiCoSO₄F and triplite LiMnSO₄F. With this study, we propose ‘ionic liquid grafting’ as an interfacial route to enable good Li-ion conductivity in otherwise poor conducting ceramics.     

Magnetisation reversal in cylindrical nickel nanobars involving magnetic vortex structure: A micromagnetic study

A three-dimensional, Fast-Fourier-Transformed (3D-FFT) micromagnetic simulation was employed to study the magnetization reversal mechanisms in cylindrical nickel nanobars possessing magnetic vortices. Individual Ni nanobars of height 150–250 nm with aspect ratio varying from 2.1 to 2.5 were considered, all of them supporting magnetic vortices domains. Magnetization reversal in these nanobars involves the vortex-creation–annihilation (VCA) mechanism with an inversion symmetry feature observed mid-way during reversal process. The effect of incidence angle of externally applied field on overall magnetization reversal process is examined in detail. The corresponding variations in coercivity, squareness, exchange energy and vortex parameters are described by the micromagnetic study that can shed insights for building practical Ni nanobars magnetic nanostructures/devices.