Neutron powder diffraction and inelastic scattering study of the structures of Zr2Pd, Zr2PdD1.70 and Zr2PdD1.96

The compounds Zr2Pd, Zr2PdD1.70 and Zr2PdD1.96 have been studied using neutron powder diffraction and the Rietveld method of profile analysis. All three materials crystallize with the symmetry of space group I4/mmm, Z=2. The lattice parameters are a=3.3085(9) A and c=10.8907(6) A for Zr2Pd, a=3.3207(2) A and c=11.6058(9) A for Zr2PdD1.70, and a=3.3715(3) A and c=11.438(2) A for Zr2PdD1.96. The deuterium atoms are located at the centres of slightly distorted tetrahedra of zirconium atoms with a Zr-D distance of 2.071(1) A in Zr2PdD1.70 and 2.092(2) in Zr2PdD1.96 and with Zr-D-Zr angles ranging from 106.60 to 110.90. The location of hydrogen in the structure has been confirmed by neutron inelastic scattering measurements. These show a broad hydrogen vibration peak at 135 meV analogous to that observed for hydrogen bound in relatively undistorted tetrahedral sites in other hydrides. As a consequence of the insertion of deuterium in the structure of the intermetallic compound, the Zr-Zr distances in the deuterides are considerably different from the corresponding ones in Zr2Pd. However, the Zr-Pd separation remains practically identical in the three materials. (orig.)