Ln-4f/ligand-2p covalence in BaLnO₃ and Cs₃LnF₇ (Ln=Ce, Pr, Tb)

Detailed information on Ln-4f/ligand-2p covalence and on differences in covalence between tetravalent Ln compounds with oxygen and fluorine was derived from Ln-M_4,5 XANES and Ln-3d XPS spectra of BaLnO₃ and Cs₃LnF₇ (Ln=Ce, Pr, Tb). We show that the fine structures of the multi-peaked spectra can be well reproduced by calculations based on the single-impurity Anderson model supplemented by intra-atomic multiplet interaction. In this way, discrepancies between experiment and theory in previous studies of LnO₂ compounds could be resolved, like the question of covalence, which we find to be weaker for Tb(IV) as compared to Ce(IV) and Pr(IV) compounds.