Hydrogenation studies on NdScSi and NdScGe

NdScSi and NdScGe were synthesized from the elements via arc-melting and subsequent annealing. Their ordered La₂Sb type structures, with space group I4/mmm, were refined from single crystal X-ray diffractometer data: a=428.94(6) and b=1570.5(3) pm, wR2=0.0395, 309 F² values for NdScSi and a=431.2(1) and c=1581.3(5) pm, wR2=0.1220, 227 F² values for NdScGe, with 11 variables per refinement. Hydrogen insertion was performed on both Nd-based intermetallics by solid/gas reaction. Hydrogen uptake keeps the pristine compound space group but yields an anisotropic expansion of the unit cell with a large increase of c (≈+7%) and a slight decrease of a (≈−1.7%) parameters. Hydrogen absorption at 350 °C and under 5 bar of H₂ pressure shows that the hydride NdScSiH_1.48(5) is formed. An in-situ neutron diffraction study during the deuteration of NdScSi reveals for the first time in a CeScSi-type compound, the possibility to fill two interstitial sites with deuterium atoms, leading to the composition NdScSiD_1.5 for the deuteride adopting then the La₂Fe₂Se₂O₃-type structure. From magnetization measurements, we evidence that hydrogenation strongly reduces the Curie temperature of NdScSi (T_C=175 K) and NdScGe (T_C=194 K) since NdScSiH_1.5 and NdScGeH_x undergo a magnetic transition at 4 K and around 2 K, respectively. - Highlights: • Crystal structures of NdScSi and NdScGe were refined from single crystal XRD data. • The hydrogenation of NdScSi leads to the formation of the NdScSiH_1.5 hydride. • NdScSiD_1.5 adopts the La₂Fe₂Se₂O₃-type structure. • Hydrogenation strongly reduces the ordering temperature of both intermetallics.