Ordered-Defect Sulfides as Thermoelectric Materials

Abstract

The thermoelectric behaviour of the transition-metal disulphides n-type NiCr 2 S 4 and p-type CuCrS 2 is investigated. Materials prepared by high-temperature reaction were consolidated using cold-pressing and sintering, hot-pressing (HP) in graphite dies or spark-plasma sintering (SPS) in tungsten carbide dies. The consolidation conditions have a marked influence on the electrical transport properties. In addition to the effect on sample density, altering the consolidation conditions results in changes to the sample composition, including the formation of impurity phases. Maximum room-temperature power factors are 0.18 mW m-1 K-2 and 0.09 mW m-1 K-2 for NiCr 2 S 4 and CuCrS 2 , respectively. Thermal conductivities of ca. 1.4 and 1.2 W m-1 K-1 lead to figures of merit of 0.024 and 0.023 for NiCr 2 S 4 and CuCrS 2 , respectively.

Effect of the Order-Disorder Transition on the Electronic Structure and Physical Properties of Layered CuCrS2

“…The positive sign of S indicates the p -type conductivity. This fact is in good agreement with previously reported data [ 11 , 12 , 13 , 14 , 15 , 16 ]. Note that the treatment procedure does not affect the conductivity type.…”

“…The thermoelectric properties of copper-chromium disulfide and CuCrS 2 based solid solutions are significantly influenced by the synthesis conditions and the sample preparation procedure [ 11 , 12 , 13 , 14 , 15 , 16 ]. Thus, it is particularly interesting to analyze the dependence of the Seebeck coefficient on the sample treatment procedure.…”

“…Copper-chromium disulfide CuCrS 2 is considered to be a promising functional material for electronic devices. Undoped copper-chromium disulfide and CuCrS 2 based solid solutions exhibit a wide range of physical properties such as thermoelectricity [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], ionic conductivity [ 17 , 18 , 19 , 20 , 21 ] and various magnetic properties [ 22 , 23 , 24 ]. Thanks to the combination of ionic conductivity and thermoelectric properties (the Seebeck coefficient, electric and thermal conductivities, ZT) demonstrated by CuCrS 2 and similar layered transition metal dichalcogenides MCrX 2 (M = Cu, Ag; X = S, Se), these compounds can be considered phonon glasses.…”

Does Low‐Level Substitution Aid in Improving Thermoelectric Properties? A Case Study of M0.1Ni0.9Cr2S4 (M = Mn, In)

“…Exemplary performances have, for example, been achieved with CuCrS2, which appeared highly suitable for thermoelectric applications and exhibited performances very similar to the established tellurides. [12][13][14][15] Structurally similar, but less investigated is NiCr 2 S 4 , which appears as a so-called ordered defect phase. [16,17] The thermoelectric properties of this material depend highly on the order and occupation of cations in their defect layers, which can subsequently be manipulated to affect conduction properties as well as the material's phase.…”

“…[17,21] Pure NiCr 2 S 4 compacted via field-assisted sintering technique (FAST) shows n-type semiconducting behavior [15,21,[24][25][26] and a thermoelectric power factor of 0.18 mW K À2 m, [15] with a slight increase at elevated temperatures (0.27 mW K À2 m at 267 C). [15] In earlier studies, we observed an electrical conductivity of 2080 S cm À1 at room temperature, [21] which already displays a character more in the range of a metal than a semiconductor and therefore inclines further improvements toward minimizing the thermal conductivity. As electrical conductivity and the electric contribution to the thermal conductivity are directly linked according to the Wiedemann-Franz law, the focus should be set on reducing the lattice contribution of the thermal conductivity.…”