An empirical rule concerning the asymmetry of the electric field gradient at a copper nucleus which is nearest neighbour to an impurity in dilute copper alloys

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Abstract
The electric field gradients (EFGs) at the nearest neighbours to impurities in dilute copper alloys have been determined experimentally for a large number of impurities. The principal directions of these EFGs are fixed by symmetry, being parallel and perpendicular to the direction towards the impurity. It is proposed that the most interesting EFG quantity might be the difference Delta between the two perpendicular components. Furthermore it is pointed out that Delta experimentally turns out to be almost proportional to the effective impurity charge Zeff with Delta /Zeff=0.22 AA-3/electron charge. This is in contrast to the other EFG parameters, which vary quite unsystematically with the impurity type.