Hysteresis behaviour of electrical resistance of the Pd - H system measured by a gas-phase method

Abstract

The hysteresis behaviour of electrical resistance during the absorption - desorption processes in the -, - and -phase regions of the Pd - H system, respectively, have been investigated at 323 K by a gas-phase method. A small extent of hysteresis in relative electrical resistance over the cyclic absorption - desorption processes in the single-phase region has been observed, showing slightly larger -values for desorption processes than for absorption processes, where is the initial resistance of a hydrogen-free sample. In cyclic desorption - absorption scans commencing from the absorption branch of p - c isotherms in the two-phase plateau region, similar hysteresis loops to those of p - c isotherms have been observed for plots of versus [H]/[Pd]. On the other hand, for cyclic desorption - absorption scans starting from absorption pressures, corresponding to hydrogen concentrations near the -phase boundary composition, -values do not return to those of desorption plateau in the two-phase region. Values of relative resistance over subsequent desorptions from absorption pressures with MPa decrease gradually with decreasing H content down to -phase boundary compositions and exhibit almost the same values as those observed for the absorption processes and, on entering the two-phase region, the -values remain almost constant with decreasing [H]/[Pd], i.e. at at 323 K. The large hysteresis of resistance relationships can be attributed to creations of lattice strains accompanied by dislocation formation arising from -phase hydride transitions and by further highly dissolved hydrogen in the -phase region.