RE Ni 9 In 2 ( RE = Rare‐Earth Metal): Crystal Chemistry, Hydrogen Absorption, and Magnetic Properties

A series of RE Ni 9 In 2 compounds ( RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) and their hydrides, RE Ni 9 In 2 H x ( 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 YNi 9 In 2 structure type [space group (SG) P 4/ 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 RE Ni 9 In 2 H x with slightly expanded unit cells within the YNi 9 In 2 structure type. Possible hydrogen positions in EuNi 9 In 2 H 3.4 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. EuNi 9 In 2 reveals ferromagnetism below approximately 40 K, which might be due to a secondary phase. Its hydride is Pauli paramagnetic, thus indicating the Eu 3+ state. YNi 9 In 2 and LaNi 9 In 2 are Pauli paramagnets. The studied phases are typical metallic conductors.