Orthorhombic NdNiSnD with filled TiNiSi-type structure

NdNiSnD deuteride (a=7.21707(9); b=8.39695(11); c=4.35618(6) Angstrom) has been synthesised from the NdNiSn equiatomic intermetallic compound and characterised by powder neutron and synchrotron X-ray diffraction and thermal desorption spectroscopy. A completely ordered deuterium insertion into half of the available Nd3Ni tetrahedral sites gives a significant deformation of the orthorhombic TiNiSi-type metal matrix. The transformation is accompanied by a decrease in lattice symmetry from space group Pnma to its related subgroup Pna2(1) with a small volume expansion of 1.9% proceeding exclusively along the [010] direction (9.1%). The Nd3Ni tetrahedra occupied by deuterium atoms share common vertexes and edges formed by neodymium atoms and build isolated columns aligned along [001]. The shortest interatomic distances are: Nd-D=2.253(12) Angstrom; Ni-D=1.568(10) Angstrom; Sn-D=3.31(2) Angstrom; D-D=2.67(2) Angstrom. A reversible formation of NdNiSn from the deuteride takes place in vacuum at 750 K, with a peak of D evolution at 660-700 K. (C) 2002 Elsevier Science B.V. All rights reserved.