The electric field gradient at Gd nuclei in intermetallic compounds with CaCu5 related structures

¹⁵⁵Gd Mössbauer spectroscopy was used to measure the electric field gradient (EFG) at the Gd nucleus in GdT₅ compounds (T=Co, Ni, Cu and Rh) and GdT₃B₂ compounds (T=Rh, Ru and Co). The crystal structure of these compounds is of the CaCu₅ type. Using the results of self-consistent band structure calculations of the valence electron contributions to the EFG, it is shown that the main contribution, comes from the asphericity of the Gd 6p valence electron charge density.