Neutron diffraction investigation of the dhcp and hcp iron hydrides and deuterides

Iron hydride and deuteride with thr dhcp metal lattice and iron deuteride with the hcp lattice were prepared under high hydrogen or deuterium pressures and studied by neutron diffraction in a metastable state at ambient pressure and 90 K. The crystal structures of the obtained phases wire refined using the Reitveld method. The composition of the dhcp phase is close to FeH1.0 or to FeD1.0 and its metal lattice contains many stacking faults in agreement with the previous data, Hydrogen or deuterium atoms in this phase occupy all available octahedral interstitial 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 structure). The hcp phase is identified with the non-magnetic phase observed earlier in the Mossbauer spectra of Fe-H and Fe-D samples ar 4.2 K. (C) 1998 Elsevier Science S.A.