RENi9In2 (RE = Rare-Earth Metal): Crystal Chemistry, Hydrogen Absorption, and Magnetic Properties

A series of RENi9In2 compounds (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) and their hydrides, RENi9In2Hx (RE = La, Ce, Pr, Nd and Eu), have been synthesized and characterized using X-ray powder diffraction and magnetization measurements. All studied compounds adopt the YNi9In2 structure type [space group (SG) P4/mbm]. The lattice parameters decrease from La to Er in accordance with the lanthanide contraction. Their structure can be visualized as a packing of rare-earth 20-vertices polyhedra and Ni-centred icosahedra in an AuCu-like arrangement. The hydrogenation results in the formation of RENi9In2Hx with slightly expanded unit cells within the YNi9In2 structure type. Possible hydrogen positions in EuNi9In2H3.4 are proposed. Most of the compounds and their hydrides (with Pr and Nd) exhibit Curie-Weiss behaviour. No magnetic ordering could be detected down to T = 2 K. EuNi9In2 reveals ferromagnetism below approximately 40 K, which might be due to a secondary phase. Its hydride is Pauli paramagnetic, thus indicating the Eu3+ state. YNi9In2 and LaNi9In2 are Pauli paramagnets. The studied phases are typical metallic conductors.