NEUTRON-DIFFRACTION INVESTIGATION OF THE DHCP AND HCP IRON HYDRIDES AND DEUTERIDES

Iron hydride and deuteride with thr dhcp metal lattice and iron deuter ide with the hcp lattice were prepared under high hydrogen or deuteriu m pressures and studied by neutron diffraction in a metastable state a t ambient pressure and 90 K. The crystal structures of the obtained ph ases wire refined using the Reitveld method. The composition of the dh cp phase is close to FeH1.0 or to FeD1.0 and its metal lattice contain s many stacking faults in agreement with the previous data, Hydrogen o r deuterium atoms in this phase occupy all available octahedral inters titial sites in the metal lattice. The composition of the hcp phase is FeD0.42 +/- 0.04, deuterium atoms randomly occupying approximately 0. 42 octahedral site of the one available per formula unit (L'3 type str ucture). The hcp phase is identified with the non-magnetic phase obser ved earlier in the Mossbauer spectra of Fe-H and Fe-D samples ar 4.2 K . (C) 1998 Elsevier Science S.A.