The effect of the electronic and structural environment on the valence of cerium

Abstract

By means of a semiempirical analysis the electrostatic energy E^ of a charge immersed in the screened Coulomb potential of the total charge distribution of the metal was selected as the most appropriate parameter for correlating different cerium environments. The choice was made by determining the smallest dispersion in plots of various physicochemical parameters versus the rate of depression a of the superconducting transition temperature Tc of thorium-based alloys containing cerium impurities. The magnetic moment o f cerium, which depends on the environment, was found to have the greatest effect on the depression of Tc. E^ was found to be proportional to qT1/2. The analysis was extended to some AB¡ compounds (A = elements of groups II - V including cerium and thorium; B; = N, Sn3, Tl3, Rh3, Co2, Ir2, B6 and Be13). An empirical relationship between E^ and the volume contraction AV/V due to the formation of the compound was found. The cerium valence for any CeB; compound is deduced from the E^(Ce) value compatible with the curve of AV/V versus E^(A), taking into account the fact that the valence and atomic radius of cerium are related.