ATOMIC POSITION AND ELECTRONIC FIELD GRADIENT OF FE DOPANT IN Y-124 SUPERCONDUCTOR

We attempt to provide a model calculation of the electric field gradie nt. With reference to the observed Fe-57 Mossbauer hyperfine interacti on parameters, the effective valence and electric field gradient on di fferent Fe lattice sites have been computed for the Fe-doped Y-124 sup erconductor by means of the point-charge-effective-valence model. Acco rding to the present calculations, the sign of electric-field gradient for the pyramid Fe(B') site and the quasioctahedral Fe(B) is estimate d to be positive and negative, respectively, and furthermore Fe is fou nd to be displaced relative to the CuO plane in Y-124 superconductors.