Influence of S and Te substitutions on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11

Abstract

We report on a detailed study of the influence of S and Te substitutions for Se on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11. Two series of polycrystalline samples Ag3.8Mo9Se11-ySy (0  y  0.5) and Ag3.8Mo9Se11-zTez (0  z  0.5) were synthesized by a combination of conventional powder metallurgy technique followed by spark plasma sintering. Powder X-ray diffraction and wavelength dispersive spectroscopy indicate that both S and Te successfully substitute for Se and exhibit a low solubility limit of y ≈ z ≈ 0.5. 2Measurements of the thermoelectric properties between 2 and 800 K show that S and Te substitutions tend to lead to a more pronounced heavily-doped character with respect to Ag3.8Mo9Se11. The very low lattice thermal conductivity of these compounds ( ≈ 0.5 W m-1 K-1) can be attributed to the large thermal displacement parameters of the Ag atoms. Despite the heavily-doped nature of the samples, the charge carriers conduct less heat than expected by the Wiedemann-Franz law resulting in significantly lower Lorenz numbers than predicted by the degenerate limit above 300 K. The combination of favourable electronic properties and low thermal conductivity leads to interesting dimensionless thermoelectric figures of merit ZT of 0.7 near 800 K.

Unravelling the Beneficial Influence of Ag insertion on the Thermoelectric Properties of the Cluster Compound K2Mo15Se19

“…Indeed, as documented for several other Mo-based cluster compounds, the Hall signal is often composed of electron-like and hole-like contributions which tend to cancel out. [14][15][16][17][18][19][20][21][22][23] The total thermal conductivity , shown in Figure 9c, exhibits a similar linear temperature dependence in both compounds, varying upon warming from 1.0 and 1.2 W m -1 K -1 at 300 K to 1.6 and 2.0 W m -1 K -1 at 800 K in the Ag3K2Mo15Se19 and K2Mo15Se19 compounds, respectively. The electronic thermal conductivity has been estimated using the Wiedemann-Franz law = / where is the Lorenz number (Figure S10 in Supporting Information).…”

“…[3][4][5][11][12][13] However, the thermoelectric properties of some of these ternary and quaternary molybdenum chalcogenides have only been assessed recently. [14][15][16][17][18][19][20][21][22][23] Their inherent structural complexity, arising from a high number of atoms per unit cell and the presence of cations in the inter-cluster voids, is the key ingredient leading to very low lattice thermal conductivity ℎ .…”

“…Combined with electrical properties that can gradually evolve from metallic to semiconductinglike by inserting additional cations, this property can potentially yield high dimensionless thermoelectric figures of merit = 2 / ( + ℎ ) which determine the efficiency of a thermoelectric material at an absolute temperature . [14][15][16][17][18][19][20][21][22][23] The main challenge then lies in achieving concomitantly high thermopower , low electrical resistivity , and low electronic thermal conductivity .…”

Chevrel Phases: Genesis and Developments

“…The filling of all bonding orbitals leads to an optimal VEC of (13n-2) for even n (refer to the value of 24 for CP, with n=2) and (13n-3) for odd n. Also, a large HOMO-LUMO gap is maintained in all these compounds [116,117] Then, depending on the filling of the MO, i.e. the counter-cation stoichiometry, semi-metallic behavior [112] and semiconductivity [107] of these condensed cluster compounds exhibit superconductivity with Tc in the range 1.7-4 K [110]. In the example of Tl 2 Mo 6 Se 6 (Tc = 2.2 K) a very high anisotropy of the critical field was reported [119], as expected from its strongly anisotropic structure.…”

Tl0.6Mo3S5, an original large tunnel-like molybdenum sulfide with Mo zigzag chains and disordered Tl cations

“…Despite the random distribution of Tl atoms in the tunnels of the crystal structure and their extended electronic density, Tl 0.6 Mo 3 S 5 shows larger values (3.8 W m -1 K -1 at 300 K) than those usually observed in Mo-based cluster compounds (between 0.5 and 1.0 W m -1 K -1 at 300 K). [10][11][12][13][14][15][16][17][18][19][20][21][22][23] The inherent disorder caused by the Tl atoms in the tunnels nevertheless likely explains the absence of low-temperature Umklapp peak in .…”