Valence band structure and charge distribution in the layered lanthanide-doped CuCr0.99Ln0.01S2 (Ln\u2009=\u2009La, Ce) solid solutions

E V Korotaev,I Yu Filatova,A V Sotnikov,A V Kalinkin,M M Syrokvashin

doi:10.1038/s41598-021-98350-9

E V Korotaev, I Yu Filatova + Show 3 more

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https://doi.org/10.1038/s41598-021-98350-9

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Abstract

The comprehensive study of the electronic density distribution of CuCr0.99Ln0.01S2 (Ln = La, Ce) solid solutions was carried out using both X-ray photoelectron and emission spectroscopy. It was found that cationic substitution of chromium with lanthanum or cerium atoms does not significantly affect the atomic charges of the matrix elements (Cu, Cr, S) in the lanthanide-doped solid solutions. The copper atoms in the composition of CuCrS2-matrix and the lanthanide-doped solid solutions were found to be in the monovalent state. The chromium and lanthanide atoms were found to be in the trivalent state. This fact indicates the isovalent cationic substitution character. The sulfur atoms were found to be in the divalent state. The near-surface layers contain the additional oxidation forms of sulfur (S0, S4+, S6+) and copper (Cu2+) atoms. The detailed analysis of the valence band structure using DFT calculations has shown that partial DOS distribution character of the matrix elements is preserved after the cationic substitution. The experimental valence band spectra structure of CuCrS2-matrix and CuCr0.99Ln0.01S2 is determined by the occupied copper d-states contribution. The contribution of the lanthanide states in the valence band structure is lower in comparison with those for the matrix elements. The major contribution of the lanthanide states was found to be mainly localized near the conduction band bottom.

Highlights

The comprehensive study of the electronic density distribution of CuCr0.99Ln0.01S2 (Ln = La, Ce) solid solutions was carried out using both X-ray photoelectron and emission spectroscopy
The electronic density and the atom oxidation state comprehensive study was carried out using experimental (XPS and X-ray emission spectroscopy (XES)) techniques and density functional theory (DFT) calculations
It was shown that cationic substitution does not significantly affect the atomic charges and the partial density of states (DOS) distribution character on the matrix elements (Cu, Cr, S)

Summary

Introduction

The Seebeck coefficient of CuCrS2-based solid solutions is significantly changed due to the reconfiguration of the electronic structure across the MIT This fact allows one to conclude that the partial density of states (pDOS) localization character and, thereby, the integral charge distribution are the key aspects of the interpretation and prediction of the thermoelectric properties. The X-ray photoelectron (XPS) and X-ray emission spectroscopy (XES) are the most effective experimental techniques to study the electronic structure[12,13] The combination of these techniques allows one to investigate the atom oxidation state in the near-surface layers (XPS) and in the bulk (XES) of CuCr0.99Ln0.01S2 (Ln = La, Ce). The partial contributions in the electronic structure features in the valence band (VB) could be studied using the density functional theory (DFT) simulation of the experimental XPS VB spectra structure

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