STRUCTURAL PHASE-TRANSITIONS OF FETI-DEUTERIDES

Absorption and desorption isotherms of FeTiDx (0≤x≤1.9) were measured at room temperature. They indicate isotope effects. The dependence of the crystal structure of FeTiDx on D2-pressure (≤153 bar) was investigated at room temperature by means of neutron diffraction on powder samples both in absorption and desorption. The results show that the distribution of the deuterium atoms in the orthorhombic β-phase change from 0.88 0.12 for the DI/DII sites at x=1.0 (1) to 0.92 0.45 at x=1.4. This can be interpreted as a transition from a β1-phase of composition FeTiD to a β2-phase of approximate composition (FeTi)3D4. For the last composition Lebsanft (2) has reported a 0.70 0.70 distribution over the two D-sites. In agreement with (3) the structure of γ-FeTiD (x>1.9) is found to be monoclinic (space group P2 m). Associated with considerable lattice expansions deuterium atoms occupy both in β- and γ-phases octahedral sites. © 1979.