EFFECT OF 2ND NEIGHBORS ON THE CRYSTAL-FIELD IN RARE-EARTH COMPOUNDS

In order to improve the covalo-electrostatic model for the calculation of crystal field parameters (CFPs): B(q)k (k = 2, 4, 6), the interaction of the rare earth ligands with second neighbours is taken into account, in addition to the central ion <-> ligands interaction. Simple empirical rules are utilized: the total CFP is the sum of an electrostatic and a covalent contribution. Furthermore, second neighbours are allowed to interfere in the covalent process if their distance to the central ion is lower than 3.5 angstrom. The resulting ratios of experimental over calculated CFP strengths for k = 2, 4 and 6 are improved. The special behaviour of compounds with second neighbours belonging to column IIIA of the periodic table is stressed. The ultimate aim is to make the prediction method reliable, whatever the rare earth and whatever the compound.