Electromigration of hydrogen in vanadium, niobium and tantalum

Abstract

The electromigration of hydrogen in VHx, NbHx and TaHx (with x approximately=0.01) has been studied between 275 and 525K using a new experimental technique. In this method the evolution of the hydrogen concentration profile during the migration process is detected by measuring capacitatively the local dilatation of the sample. From the temperature dependence of the effective valence Z* of hydrogen is is concluded that the valence associated with the direct force in electromigration is essentially different from the bare valence of a proton for Nb and Ta, whereas for V a value close to +1 is found. The 'wind-force' contribution to Z* is for all metals under consideration of the same order of magnitude as the direct force. In V and Nb the wind force has the same sign as the direct force, whereas an opposite sign is found in Ta. The results are discussed within the framework of existing theories of electromigration.