Properties of an extended periodic Anderson model with the f-c Coulomb interaction is studied as a model for and related compounds which is cosidered to exhibit a sharp valence change under pressure. The problem is treated by extending the { slave-boson} and large-N expansion method to treat the present system. It is shown that, as the f-level εf is increased relative to the Fermi level, the sharp valence change is caused by the effect of with moderate strength of the order of the bandwith of conduction electrons. The superconducting transition temperature T_ due to the valence-fluctuation exchange is estimated on the slave-boson fluctuation approximation. In the model with spherical Fermi surface, T_ exhibits sharp peak as a function of εf, simulating the effect of pressure, for the d-wave pairing channel.
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Onishi et al. (2000) studied this question.