Hydrogenation studies on NdScSi and NdScGe

•Crystal structures of NdScSi and NdScGe were refined from single crystal XRD data.•The hydrogenation of NdScSi leads to the formation of the NdScSiH1.5 hydride.•NdScSiD1.5 adopts the La2Fe2Se2O3-type structure.•Hydrogenation strongly reduces the ordering temperature of both intermetallics.

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 NdScSiH1.48(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 NdScSiD1.5 for the deuteride adopting then the La2Fe2Se2O3-type structure.From magnetization measurements, we evidence that hydrogenation strongly reduces the Curie temperature of NdScSi (TC=175 K) and NdScGe (TC=194 K) since NdScSiH1.5 and NdScGeHx undergo a magnetic transition at 4 K and around 2 K, respectively.

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