High-pressure synthesis of Mg2FeH6 complex hydride

We have designed a new synthesis method for the ternary metal hydride Mg2FeH6 based on the direct reaction of simple hydrides under high-pressure conditions. Well-crystallized samples were prepared in a piston-cylinder hydrostatic press at 2 GPa and temperatures around 750 °C from mixtures of MgH2 and Fe enclosed in gold or platinum capsules. Seven different samples have been prepared under different conditions. X-ray powder diffraction analysis was used to identify and assess the purity of the samples, through Rietveld analyses of the crystal structure (K2PtCl6-type). Mg2FeH6 shows a cubic symmetry with space group Fm-3m. SEM images show an average particle size of 1–2 μm for Mg2FeH6; the microcrystals present well-grown faces and display a high homogeneity of shapes and sizes. Thermogravimetric analysis has been carried out to determine not only the hydrogen desorption temperature but also the hydrogen contents.