ELECTRICAL-RESISTANCE MEASUREMENTS AS A FUNCTION OF COMPOSITION OF PALLADIUM-HYDROGEN(DEUTERIUM) SYSTEMS BY A GAS-PHASE METHOD

The simultaneous measurement of both the relative electrical resistanc e and the equilibrium hydrogen and deuterium pressure as a function of composition of Pd-H and Pd-D systems have been carried out at tempera tures between 273 and 323 K at H-2(D-2) pressures up to about 3.3 MPa. The relative resistance, R/R(o), in the (alpha+beta) two-phase region for the absorption processes shows a very small and almost linear inc rease with increasing H(D) content, especially for the Pd-H system, co mpared to the larger changes previously observed by the electrolysis m ethod. The resistance behaviour is quite similar to the shape of p-c i sotherm relationships. The relative resistance increments per unit cha nge of H(D)/Pd content at 298 K, Delta(R/R(o))/Delta r, in the (alphabeta) two-phase region are about 1.5 and 2.1 times larger for the Pd-H and Pd-D systems, respectively, compared to the changes in the relati ve lattice parameters with H(D)/Pd content, Delta(a/a(o))/Delta r, wit hin the two-phase region, where a(o) is the lattice parameter of H(D)- free Pd and r is the atom ratio. On the other hand, the resistance inc rement in the alpha single solid solution phase and beta single phase, except for the higher-H(D)-content legion, is significantly larger co mpared to the changes of the lattice expansion due to dissolved hydrog en and deuterium. Thus, the variation in resistance with hydrogen and deuterium content in the (alpha+beta) two-phase region may be mainly a ssociated with an incoherent formation of beta hydride within the alph a phase. The relative resistance for the subsequent desorption process es from the absorption up to about 3.3 MPa at 298 K in both Pd-H and P d-D systems exhibits almost the same maximum as that of the absorption processes, i.e. (R/R(o))(H,max) similar or equal to 1.87 at about H/P d = 0.76 and (R/R(o))(D,max) similar or equal to 2.07 at about D/Pd = 0.75, and then the R/R(o) values decrease gradually with decreasing H( D) content up to the beta(min) phase boundary composition; on entering the (alpha+beta) two-phase region, the R/R(o) values remain almost co nstant, i.e. (R/R(o))((alpha+beta)) similar or equal to 1.76 for the P d-H system and (R/R(o))((alpha+beta)) similar or equal to 1.89 for the Pd-D system. This large hysteresis of resistance can be attributed to the creation of 'lattice strain deformations' accompanied by dislocat ion formation from beta hydride (deuteride) formation and by further h ighly dissolved hydrogen and deuterium in the beta phase region.