Effect of Sn Substitution on the Thermoelectric Properties of Synthetic Tetrahedrite

Abstract

The present study reports the effect of Sn substitution on the structural and thermoelectric properties of synthetic tetrahedrite (Cu 12 Sb 4 S 13) system. The samples were prepared with the intended compositions of Cu 12 Sb 4−x Sn x S 13 (x = 0.25, 0.35, 0.5, 1) and sintered using spark plasma sintering. A detailed structural characterization of the samples revealed tetrahedrite phase as the main phase with Sn substituting at both Cu and Sb sites instead of only Sb site. The theoretical calculations using density functional theory revealed that Sn at Cu(1) 12d or Cu(2) 12e site moves the Fermi level (E F) toward the band gap, whereas Sn at Sb 8c site introduces hybridized hole states near E F. Consequently, a relatively high optimum power factor of 1.3 mW/mK 2 was achieved by the x = 0.35 sample. The Sn-substituted samples exhibited a significant decrease in the total thermal conductivity (κ T) compared to the pristine composition (Cu 12 Sb 4 S 13), primarily because of reduced electronic thermal conductivity. Due to an optimum power factor (1.3 mW/mK 2) and reduced thermal conductivity (0.9 W/mK), a maximum zT of 0.96 at 673 K was achieved for x = 0.35 sample, which is nearly 40% increment compared to that of the pristine (Cu 12 Sb 4 S 13) sample.

Simultaneous optimization of power factor and thermal conductivity via Te and Se double substitution in Cu12Sb4S13 tetrahedrite

“…It should be noted that Hall measurements were attempted to evaluate the charge carrier concentration as well as to confirm the charge carrier compensation and charge carrier mobility analysis. But we could not obtain coherent and conclusive results due to low and arbitrary Hall coefficients, which was also observed in many of the previous reports [4,5,10,14].…”

Charge Transport and Thermoelectric Properties of Sn-Doped Tetrahedrites Cu12Sb4-ySnyS13

“…4+ substituted at the Sb 3+ site provided excess electrons, which reduced the carrier (hole) concentration due to charge compensation. Considering the ionic radii claimed by Tippireddy et al[20] when Sn is doped in the tetrahedrite, either Sn 4+ should be substituted at the Cu + or Cu 2+ site or Sn 2+ at the Sb 3+ site to increase the lattice constant, as shown in this study. However, if the entirety of the doped Sn is substituted at the Sb 3+ site into a Sn 2+ state, we should observe a reduction in carrier (hole) concentration.…”

“…increased with increasing temperature but decreased with increasing Sn content, resulting in a minimum electronic thermal conductivity of 0.002-0. [20].…”

“…Thus, the highest Seebeck coefficient of 192-264 μVK -1 was obtained at 300-700 K for Cu 12 Sb 2.25 Te 1.75 S 13 . Tippireddy et al[20] reported that the Seebeck coefficient decreased with increasing Sn content for Cu 12 Sb 4-x Sn x S 13 (x = 0.25-1), reaching a maximum value of 183 μVK -1 at 673 K for Cu 12 Sb 3.65 Sn 0.35 S 13 .Figure 6 presents the PF of Cu 12 Sb 4-y Sn y S 13 . Based on the temperature dependences of the electrical conductivity and Seebeck coefficient shown in Figs.…”

“…In our previous study[7], the lattice constant of undoped tetrahedrite Cu 12 Sb 4 S 13 was 1.0327 nm.Thus, the lattice constant was significantly increased by Sn substitution at the Sb site. Tippireddy et al[20] reported the ionic radii of Cu + (60 pm), Cu 2+ (57 pm), Sb 3+ (76 pm), Sn 4+ (69 pm), and Sn 2+ (118 pm). Hansen et al[21] suggested that Sn 4+ can be doped into the Cu sites when no other divalent transition elements are present in the tetrahedrite system, suggesting that Sn 2+ can be substituted at the Sb 3+ site, and Sn 4+ can be substituted for Cu + and/or Cu 2+ .…”