High-pressure synthesis of Na1−xLixMgH3 perovskite hydrides

► New synthesis method for the ternary metal hydride perovskite system Na1−xLixMgH3. ► Direct reaction of simple hydrides under high-pressure and high-temperature conditions. ► X-ray and Neutron Powder Diffraction analysis were used to identify the purity of the samples. ► Perovskite hydride structure; more distorted and unstable as Li is introduced (smaller ionic size of Li+vs Na+). ► Hydrogen desorption temperature much reduced respect to MgH2; useful as hydrogen storage materials. Magnesium base alloys are very attractive for hydrogen storage due to their large hydrogen capacity, small weight and low-cost. We have designed a new synthesis method for the ternary metal hydride perovskite system Na1−xLixMgH3, based on the direct reaction of simple hydrides under high-pressure and moderate-temperature conditions. Well-crystallized samples were obtained in a piston-cylinder hydrostatic press at moderate pressures of 2GPa and temperatures around 750°C from mixtures of MgH2, NaH and LiH enclosed in gold capsules. X-ray and neutron powder diffraction analysis were used to identify the purity of the samples and provide an accurate description of the crystal structure features (GdFeO3 type). Na1−xLixMgH3 hydrides series (0≤x≤0.18) show an orthorhombic symmetry with space group Pnma (No. 62). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) have been carried out to determine the hydrogen desorption temperatures.