The Charge Distribution, Seebeck Coefficient, and Carrier Concentration of CuCr0.99Ln0.01S2 (Ln = Dy–Lu)

Abstract

The atom oxidation states were determined using the binding energies of the core S2p-, Cu2p-, Cr2p-, and Ln3d-levels in CuCr0.99Ln0.01S2 (Ln = Dy–Lu) solid solutions. The charge distribution on the matrix elements (Cu, Cr, and S) remained unaffected after cationic substitution. The sulfur atoms were found to be in the S2− oxidation state, the copper–Cu+, and the chromium–Cr3+. The cationic substitution of the initial CuCrS2-matrix occurred via the isovalent mechanism. The obtained results were compared with the electrophysical properties for CuCr0.99Ln0.01S2. The measured carrier concentration was from 1017 to 1018 cm−3. The largest Seebeck coefficient value of 157 µV/K was measured for CuCr0.99Yb0.01S2 at 500 K. The cationic substitution with lanthanides allowed one to enhance the Seebeck coefficient of the initial CuCrS2-matrix.

Thermoelectric Properties of Layered CuCr0.99Ln0.01S2 (Ln = La…Lu) Disulfides: Effects of Lanthanide Doping

“…. .Lu) compounds were synthesized using high-purity commercial metal oxides via the previously reported sulfidation route [34]. The samples were found to be single-phase and isostructural to the initial CuCrS 2 -matrix [41].…”

“…The XRD data evidencing the cationic substitution of the chromium atoms with lanthanides and the study of the doping mechanism were reported previously [35,36,[39][40][41]. The ceramic samples were prepared by compressing the synthesized powder samples under uniaxial pressure in a vacuum [34]. The measurements of the Seebeck coefficient of the CuCr 0.99 Ln 0.01 S 2 compounds were carried out using the original experimental setup described in detail in [32,34,36].…”

“…The ceramic samples were prepared by compressing the synthesized powder samples under uniaxial pressure in a vacuum [34]. The measurements of the Seebeck coefficient of the CuCr 0.99 Ln 0.01 S 2 compounds were carried out using the original experimental setup described in detail in [32,34,36].…”

“…The combination of the aforementioned properties allows CuCrS 2 -based compounds to be considered promising materials for the fabrication of high-performance thermoelectric generators (TEGs). The cationic substitution of the CuCrS 2 -matrix is significantly affected by the thermoelectric properties of the initial matrix [32][33][34][35][36]. It was previously reported that the cationic substitution of the CuCrS 2 -matrix with a low concentration of doping atoms could enhance the thermoelectric properties of the initial matrix.…”

“…Thus, according to previous studies, a concentration of x = 0.01 is considered to be optimal. Note that the cationic substitution of chromium in the CuCrS 2 -matrix with lanthanide atoms, from lanthanum to lutecium, in CuCr 1−x Ln x S 2 has been reported to occur via the isovalent principle with Cr 3+ to Ln 3+ [34,35,39,41]. A study of compounds doped with promethium was excluded from this study due to its radioactivity and rarity.…”