Electromigration of hydrogen in alloys: Evidence of unscreened proton behavior

In an attempt to resolve the long lasting controversy about the magnitude of the direct-force valence of impurities in the theory of electromigration, the effective valence, ${\mathrm{Z}}^{\mathrm{*}}$, for interstitial hydrogen has been determined in concentrated disordered ${\mathrm{Nb}}_{1\mathrm{-}\mathrm{y}}$ ${\mathrm{V}}_{\mathrm{y}}$ alloys. ${\mathrm{Z}}^{\mathrm{*}}$ is found to be almost equal to unity independent of temperature and alloy composition. The important implication of these results is that for hydrogen in ${\mathrm{Nb}}_{1\mathrm{-}\mathrm{y}}$ ${\mathrm{V}}_{\mathrm{y}}$ alloys the direct-force valence ${\mathrm{Z}}_{\mathrm{d}}$=+1, equal to the charge of the unscreened proton, in agreement with the recent theory of Lodder.