VALENCE-ELECTRON CONTRIBUTIONS TO THE ELECTRIC-FIELD GRADIENT IN HCP METALS AND AT GD NUCLEI IN INTERMETALLIC COMPOUNDS WITH THE THCR2SI2 STRUCTURE

Self-consistent band-structure calculations have been used to calculate valence-electron contributions to the electric-field gradient (EFG) in all elemental hcp metals, except those with nonspherical 4f shells, and at Gd nuclei in numerous intermetallic compounds of the type GdT2Si2 (T=Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, and Ag) and GdNi2X2 (X=Ge and Sn). Experimental determinations of the EFG in the latter two compounds were performed by a study of the Gd155 Mössbauer effect. The calculated EFG of hcp metals agrees well with the experimental values. The variation of the EFG with the T component across a given RT2Si2 series (R=rare earth, T=3d, 4d, 5d) is shown to be mainly due to a change of the asphericity of the Gd 6p charge distribution. The trends in this asphericity have also been explained qualitatively from a more simple treatment of the electronic structure, based on Miedema s macroscopic-atom model for cohesion in metals. It is shown that as a consequence of the large valence-electron contribution to the EFG, the commonly used proportionality relation between the EFG and the second-order crystal-field parameter A20 lacks a true physical basis, and may be invalid. © 1990 The American Physical Society.