Coherent potential approximation treatment of intermediate valence in rare-earth compounds induced by alloying

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Abstract
The coherent potential approximation (CPA) is applied to the description of intermediate valence induced by alloying as observed in the solid solutions Sm1−xRxS where R denotes a rare‐earth element which is trivalent in the monosulfide. The description is based on the Falicov‐Kimball model for metal‐insulator transitions generalized to take into account the disorder associated with the R substitution. This disorder is treated within the CPA while the intra‐atomic correlation on the Sm sites is also treated by the CPA in analogy with an alloy of divalent and trivalent Sm ions. The transition to an intermediate valence for Sm as a function of alloy composition is discussed in terms of the results of this treatment.