Peculiarities of the intermediate valence state of Ce in CeM2Si2 (M = Fe, Co, Ni) compounds

The results of thermoelectric power and the electrical resistivity measurements connected with the intermediate valence (IV) of Ce are presented for the compounds CeM2Si2 (M = Fe, Co, Ni) in the temperature range of 4–800 K. It is shown that CeM2Si2 are Kondo-lattices with the coherence scale Tcoh ∼ 60–80 K and the so-called single-site Kondo temperature TK ∼ 103 K. On the example of CeNi2Si2 we have studied the changes in the structure of density of f states (f-DOS) near the Fermi energy caused by atomic substitutions. The results of structural, transport, magnetic, and Ce LIII X-ray absorption spectra measurements in the series Ce1−xLaxNi2Si2 (0 ≤ x ≤ 0.6), Ce(Ni1−yCuy)2Si2 (0 ≤ y ≤ 0.6) and CeNi2(Si1−zGez)2 (0 ≤ z ≤ 0.5) are presented. We found that the IV state of Ce in the CeM2Si2 is an evidence of possible opening a wide pseudogap Δ ∼ kTK within the f-DOS structure slightly above the Fermi energy.