The influence of the crystal field on the anisotropic thermal expansion in ErCu₂ and NdCu₂

The anisotropic thermal expansion parameters a(T), b(T) and c(T) of some RECu₂, intermetallics (RE=Y, Er, Nd) has been measured in the temperature range from 400 K down to 4.2 K using X-ray powder diffraction. The influence of the crystal field on the thermal expansion in ErCu₂ and NdCu₂ has been determined by comparing the thermal expansion of the nonmagnetic isostructural YCu₂ with the Er and Nd compounds. The data thus obtained are described theoretically using a set of crystal-field parameters deduced from the analysis of inelastic neutron diffraction data.