NEUTRON-DIFFRACTION STUDIES OF THE ZR3P-D SYSTEM

Products obtained by absorption of different amounts of deuterium in Zr3P have been investigated by X-ray and neutron diffraction methods. Crystal structure analyses were performed using the Rietveld profile refinement technique on the neutron data. In one sample, an interstitial solid solution of deuterium in Zr3P was identified. Its composition corresponded to the formula Zr3PD0.15, with the Zr3P sublattice essentially being unchanged as compared to that of the pure phosphide (Ti3P-type, space group P4(2)/n). A second more deuterium-rich sample was found to contain two phases in nearly equal amounts. One of them was a solid solution of deuterium in Zr3P of the approximate composition Zr3PD0.78, while the other phase was found to be isostructural with the Zr3PD3-x phase (sublattice of the beta-V3S-type, space group P4(2)/nbc, x almost-equal-to 0.1) reported in a previous study, its composition according to the structure refinement being close to Zr3PD2.60. In both cases, all deuterium atoms are surrounded by four near-neighbour zirconium atoms in more or less distorted tetrahedral arrangements. Assuming the action of local deuterium ordering, no D-Zr, D-P and D-D distances shorter than 1.9, 2.7 and 2.3 angstrom were observed.