Hydrogenation properties of Li_xSr_1−xAlSi studied by quantum-chemical methods (0≤x≤1) and in-situ neutron powder diffraction (x=1)

In-situ neutron powder diffraction studies of the Half-Heusler phase LiAlSi under high deuterium pressures and first principle calculations of solid solutions of Li_xSr_1−xAlSi and their hydrides Li_xSr_1−xAlSiH were carried out. In contrast to an earlier study, there is no experimental evidence for hydrogen (deuterium) uptake up to gas pressures of 15 MPa and temperatures of 550 °C. Instead a slow decomposition reaction according to LiAlSi+1/2H₂=LiH+Al+Si was found by in-situ neutron powder diffraction. Theoretical calculations by DFT methods on hypothetical solid solutions of Li_xSr_1−xAlSi show the LiAlSi type to be the energetically most stable structure for 0.7xSr_1−xAlSiH favor the SrAlSiH type for all values of x instead of the structure proposed earlier with hydrogen occupying tetrahedral voids in a LiAlSi structure. As an alternative for a cubic structure for LiAlSiH, we suggest the existence of LiAlSiH in the trigonal SrAlSiH type structure and it might be a candidate worthwhile to be considered for preparative work. - Graphical abstract: In-situ neutron powder diffraction of LiAlSi under high D₂ pressure. - Highlights: • In-situ neutron powder diffraction of LiAlSi under high D₂ pressure was carried out. • LiAlSi decomposes according to LiAlSi + ½ H₂ = LiH + Al + Si. • Mixed crystals Li_xSr_1-xAlSi and LixSr_1-xAlSiH were studied theoretically