Relationships between the electrical resistivity and the metal hydride phases

Electrical resistivity of the unstable metal hydrides LaNi5Hx and LaCo5Hx has been measured in situ by a newly developed method where the samples are under the influence of mechanical stress. An activated sample does not give the bulk resistivity of the hydride, but the resistivity change with hydrogen pressure or temperature is correlated with the transformation of hydride phases. The resistivity of the bulk hydride is tolerably obtained in the first absorption of hydrogen for a virgin sample. The resistivity at 323 K is 1.3, 15.3 and 8.5 mu Omega m for the metal phase (x = 0), the alpha phase (x similar or equal to 0.6) and the beta phase (x = 6.7) of LaNi5Hx, and 1.5, 11.5 and 18.8 mu Omega m for the metal phase (x = 0), the beta phase (x = 3.4) and the gamma phase (x = 4.3) of LaCo5Hx, respectively. These resistivity changes with hydrogen composition are interpreted in relation to disordered-ordered arrangement of hydrogen.