Electron Transport Properties of Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1): Initiation of Transition Eu2+ ↔ Eu2.41+ in the Intermediate Valence State

The article presents the results of studies of the chemical composition, crystal structure, lattice parameters, microstructure, the valence state of the europium ion (at 300 K), electrical resistivity, and differential thermopower (6–400 K) of samples in the Eu(Cu_1 − xAg_x)₂Si₂ (0 ≤ x ≤ 1) substitutional solid solutions. A transition of the europium ion from the valence-stable state of Eu²⁺ in EuAg₂Si₂ to the state of intermediate (homogeneous) valence (IV) of the europium ion in EuCu₂Si₂ with an effective valence ϑ_eff = 2.41 (300 K) has been initiated by a successive replacement of silver atoms by copper atoms. With appropriate sample compositions, the transition passes through a Kondo-type state. The research subject is the patterns of transformations (when the composition of the sample changes), the electronic state, and, accordingly, the electronic transport properties. The simultaneous coexistence of europium ions in different electronic states is assumed. The substitutional solid solution Eu(Cu_1 − xAg_x)₂Si₂ (0 ≤ x ≤ 1) exhibits properties related to the competition between the state of the Kondo system, intermediate valence (IV), and magnetic ordering.