High-performance thermoelectric minerals: Colusites Cu26V2M6S32 (M = Ge, Sn)

Abstract

We report thermoelectric (TE) properties of dense samples of colusites Cu26V2M6S32 (M = Ge, Sn), most of which are composed of earth-abundant elements; Cu and S. The combination of p-type metallic conduction and large thermopowers greater than 200 μV/K leads to high TE power factors of 0.61 and 0.48 mW/K2 m at 663 K for M = Ge and Sn samples, respectively. Furthermore, the lattice thermal conductivity is smaller than 0.6 W/Km over the temperature range from 350 K to 663 K due to the structural complexity. As a consequence, the values of dimensionless TE figure of merit ZT for M = Ge and Sn reach 0.73 and 0.56 at 663 K, respectively. Thus, the colusites are promising candidates for environmental friendly TE materials usable in the range of 500–700 K.

Research Update: Cu–S based synthetic minerals as efficient thermoelectric materials at medium temperatures

“…In fact, the CP samples with M = Ge and Sn exhibited similar p-type metallic character, ρ ∼ 4 µΩm and S ∼ 30 µV/K at 300 K. The values of ρ and S were increased by one order of magnitude by the hot-press (HP) sintering process. Probably, a portion of the sulfur evaporated, leading to the decrease in the hole carrier density p. 78 As a result, the PF's of HP-sintered samples with M = Ge and Sn reached 0.61 and 0.48 mW/K 2 m at 663 K, respectively. The first principles electronic structure calculations of colusites gave suggestions that good electronic properties originate from the VB composed mainly of Cu-3d and S-3p hybridized orbitals (Fig.…”

“…2, ZT for M = Ge and Sn reached 0.73 and 0.56 at 663 K, respectively. 78 It is noteworthy that the values of κ of the colusites are as low as the tetrahedrites and the chalcosite. The value of κ was obtained using the relation κ = αC p d, where α is the thermal diffusivity, C p is the specific heat at constant pressure, and d is the sample density.…”

“…The estimated κ L for the colusite was 0.4-0.55 W/Km at 350 K. The value was much lower than κ L ∼ 5 W/Km for the sulvanite Cu 3 VS 4 with a 1/8-sized unit cell. 78 Thus, the reduced κ L was attributed to the structural complexity: 47,80 large unit cell, large number of atoms per unit cell (N), and mass difference between Cu, V, and M. The former character is expected to lower the fraction of vibrational modes that carry heat efficiently (the acoustic modes) to 1/N.…”

“…4(b)). 78 The heavy hole effective mass, which was estimated from Hall-effect measurement, was assumed to result in the large PF. 79 The value of κ for the HP-sintered samples decreased from 0.65 to 0.55 W/Km on heating from 350 K to 673 K. As shown in Fig.…”

Copper chalcogenide thermoelectric materials

“…3a, Cu 2 Se possesses two sublattices: the rigid FCC framework of Se atoms and the disordered and flowing sublattice of Cu. At high temperatures, Cu ions migrate from one site (interstitial one formed by Se) to another, exhibiting a flowing character that is Figure 1 Timeline of zT for selected Cu-based superionic conductors [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] (red), tetragonal [28][29][30][31][32][33][34][35][36][37] (blue) and distorted [38][39][40][41][42][43][44][45][46][47][48][49] (green) diamond-like materials and BiCuSeO oxyselenides (purple) [50][51][52][53][54][55][56][57][58][59]…”