Evidence of low dimensional ion transport in mechanosynthesized nanocrystalline BaMgF4

Abstract

Mechanochemical milling provides a versatile method for the preparation of nano-sized, defect rich, polycrystalline materials. If ionic materials are considered, the transport parameters of the mobile ions may greatly differ from those of the microcrystalline counterparts prepared by conventional synthesis routes. Little is known about ionic conduction in nanocrystalline materials having crystal structures that offer spatially confined transport pathways. Here, we focused on mechanosynthesized BaMgF₄ that combines both nanocrystallinity and anisotropic F⁻ transport. The preparation of nanocrystalline BaMgF₄ is presented as a facile and rapid one-pot procedure. The reaction was followed by X-ray diffraction and high-resolution ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. NMR helped prove the formation of X-ray amorphous compounds as well as the transformation of the starting materials into the final product BaMgF₄. Most importantly, besides enhanced conduction properties compared to a single crystal, our broadband impedance spectra reveal characteristics pointing to anisotropic (low dimensional) ion transport processes even in the nanocrystalline form of BaMgF₄.