Electric quadrupole interaction in Cu-Ni and Cu-vacancy

By using the screening charge model of Alfred and Van Ostenburg (1969) for the valence effect and the continuum model of lattice strain for the size effect, electric field gradients (EFG) in Cu-Ni and Cu-vacancy are calculated at the first four nearest-neighbour host sites. The strain-field gradient coupling parameter lambda has been fixed by fitting the calculated EFG at the fourth nearest neighbour with experiment. The results show that except for the discrepancy in the principal Z direction of the EFG tensor at the first nearest neighbour in Cu-Ni and in the magnitudes of the EFG at the second nearest neighbours, there is good agreement between theory and experiment in both the systems. Possible reasons for the existing discrepancy are discussed.