Phonon Scattering through a Local Anisotropic Structural Disorder in the Thermoelectric Solid Solution Cu₂Zn_1–xFe_xGeSe₄

Abstract

Inspired by the promising thermoelectric properties of chalcopyrite-like quaternary chalcogenides, here we describe the synthesis and characterization of the solid solution Cu 2 Zn 1−x Fe x GeSe 4 . Upon substitution of Zn with the isoelectronic Fe, no charge carriers are introduced in these intrinsic semiconductors. However, a change in lattice parameters, expressed in an elongation of the c/a lattice parameter ratio with minimal change in unit cell volume, reveals the existence of a three-stage cation restructuring process of Cu, Zn, and Fe. The resulting local anisotropic structural disorder leads to phonon scattering not normally observed, resulting in an effective approach to reduce the lattice thermal conductivity in this class of materials.

Band convergence in the non-cubic chalcopyrite compounds Cu2MGeSe4

“…[21][22][23][24][25][26] Furthermore Zeier et al have shown that a restructuring process in the series of solid solutions Cu 2 Zn 1Àx Fe x GeSe 4 changes the c/2a axis ratio, which leads to enhanced point defect scattering and a reduction in the thermal conductivity due to the high local anisotropic structural disorder. 27 The changing bond angles and bond lengths in these materials strongly inuence the thermal transport properties in these materials.…”

“…In the kesterite type Cu 2 FeGeSe 4 , band convergence should be obtained at a critical value of c/2a above unity. The combination of increasing power factor, due a valence band convergence, and the lower lattice thermal conductivity, due to point defect scattering, 27 leads to an increase of the gure of merit with increasing c/2a (see Fig. 5b).…”

Bond strength dependent superionic phase transformation in the solid solution series Cu2ZnGeSe4−xSx

“…8 The structure of the stannite-type solid solution series Cu 2 ZnGeSe 4Àx S x (space group I 42m) is shown in Fig. 1.…”

“…While the mobile copper cations result in a "phonon-liquid electron crystal" type behavior in this class of superionic materials resulting in low heat capacities, 1,2 the inherent structural disorder leads to low thermal conductivities in compounds such as Cu 2 Zn(Sn/Ge)Se 4 (ref. [3][4][5][6][7][8] and CuGaSe(Te) 2 .…”

Enhanced Thermoelectric Properties of Cu3SbSe4 Compounds via Gallium Doping

“…Recently, copper-based chalcogenide semiconductors have attracted much attention because of their relatively high carrier mobility (µ H ) and low κ, such as CuGa(In)Te 2 , Cu 2 CdSnX 4 (X = Se, S), Cu 2 SnSe 3 , and Cu 3 SbSe 4 [11][12][13][14]. Among these compounds, ternary Cu 3 SbSe 4 semiconductor has emerged as a promising thermoelectric material because of its narrow band gap and large carrier effective mass.…”