STUDY OF THE VALENCY OF RARE-EARTH ATOMS IN THE MISFIT-LAYER COMPOUNDS (RS)1+DELTA-NBS2 (R = LA, CE, SM) USING RESONANT PHOTOEMISSION AND X-RAY-ABSORPTION SPECTRA

The photoelectron spectrum of (CeS)1.16NbS2 shows a strong resonance enhancement at a photon energy of 120 eV for states with a binding energy of 2.4 eV. The resonance is due to Ce 4d(10)4f1-->4d(9)4f2 transitions, and is evidence that the Ce atoms in this compound have the valency Ce3+ (4f1). The 3d x-ray-absorption spectrum of (LaS)1.14NbS2, (CeS)1.16NbS2, and (SmS)1.19NbS2 exhibit a multiplet structure which is characteristic for La3+ (4f0), Ce3+ (4f1), and Sm3+ (4f5). We conclude that in the misfit-layer compounds (RS)1+deltaNbS2 (R = La,Ce,Sm) the rare-earth atoms are trivalent.