Charge Distribution in Layered Lanthanide-Doped CuCr_0.99Ln_0.01S₂ (Ln = Pr-Tb) Thermoelectric Materials

The charge distribution study of metal atoms in CuCr_0.99Ln_0.01S₂ (Ln = Pr-Tb) solid solutions was carried out using X-ray photoelectron spectroscopy (XPS). The analysis of the binding energy of S2p, Cu2p, Cr2p, Ln3d and Ln4d levels allows one to determine the oxidation state of atoms. Copper atoms were found to be monovalent. Chromium and lanthanide atoms were found to be in the trivalent state. Sulfur atoms were found to be in the divalent state. Cationic substitution was found to occur via an isovalent mechanism of Cr³⁺ to Ln³⁺. The obtained results were used for the interpretation of the Seebeck coefficient increase for CuCr_0.99Ln_0.01S₂ solid solutions in contrast to the initial CuCrS₂ matrix. The largest Seebeck coefficient values of 142 and 148 µV/K were observed at 500 K for CuCr_0.99Sm_0.01S₂ and CuCr_0.99Pr_0.01S₂, respectively. The obtained values are 1.4 times greater in comparison with those for the initial matrix (105 µV/K).