Does Low‐Level Substitution Aid in Improving Thermoelectric Properties? A Case Study of M_0.1Ni_0.9Cr₂S₄ (M = Mn, In)

Abstract

Recent interest in renewable, sustainable concepts for energy production led to an increasing spotlight on thermoelectric materials, being an environmentally friendly means of continuous power generation from waste heat. Established and wellresearched materials with high efficiencies such as Sb 2 Te 3 , [1][2][3][4] Bi 2 Te 3 , [1][2][3][4] or PbTe [5][6][7] generally suffer from low abundance of the included elements, cost-inefficiency and environmental issues, which ultimately inhibit their large-scale applicability. An alternative exists in chromium sulfides, [8][9][10] whose thermoelectric properties have already been reported in the 1960s: [8] the high abundance of Cr and S as well as a reasonable environmental footprint make them promising candidates, even though their initial efficiency appears lower than in established materials. [11] In turn, their compositional flexibility and variability of the crystal structures allow for a plethora of possibilities to improve and tune their thermoelectric properties. 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. Furthermore, it has been reported that layered chromium sulfides generally retain their pristine structure while being doped or

About the Impact of Defect Phases on the Thermoelectric Properties of Cr3S4–xSex

“…[ 26 ] In contrast, additional phases or atom impurities may prove beneficial for the thermal conductivity, which is lowered by introducing additional scattering centers for phonons. This has been applied to the structurally similar system NiCr 2 S 4 in previous studies [ 27 ] with substitutions in the cation sublattice. Pisharody et al proved that substitutions in the anion sublattice (i.e., S replaced by Se) could also positively impact the thermoelectric performance by reducing the thermal conductivity.…”