Experimental Results on Hydrogen Jump Diffusion Mechanisms

Experimental Results on Hydrogen Jump Diffusion Mechanisms 

Detailed atomistic information of the elementary process of jump diffusion can be obtained from QENS at Q values comparable with the inverse jump distances, i.e. at large Q [14,28,29]. Hydrogen in the a-phases of the cubic f.c.c. and b.c.c. metals Pd, Nb, Ta and V was investigated very early, and the quite detailed results which are now available will be outlined first in Section 26.4.1. One of the rare cases where a hydride single crystal was available is y9-V2H, and the corresponding QENS study will be presented in some more detail in the second part of Section 26.4.1. 

The theoretical basis of all these QENS studies is the Chudley-Elliott model [59], which in its basic form involves the following postulates. 

All sites involved in the diffusion process are crystallographi-cally and thus also energetically equivalent (Bravais sublattice). 

All jumps (to nearest neighbor sites only) have the same jump length f and are characterized by jump vectors S , i = 1, 

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Experimental Results on Hydrogen Jump Diffusion Mechanisms 801... 

These features may give rise to a coexistence of several types of H motion with different characteristic jump rates. Here we shall discuss the experimental results on hydrogen jump diffusion mechanisms in a number of representative interme-tallic compounds. A comprehensive review of the experimental studies in this field before 1992 can be found in Ref [11]. 

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