Influence of a Nano Phase Segregation on the Thermoelectric Properties of the p-Type Doped Stannite Compound Cu_2+xZn_1–xGeSe₄

Abstract

Engineering nanostructure in bulk thermoelectric materials has recently been established as an effective approach to scatter phonons, reducing the phonon mean free path, without simultaneously decreasing the electron mean free path for an improvement of the performance of thermoelectric materials. Herein the synthesis, phase stability, and thermoelectric properties of the solid solutions Cu(2+x)Zn(1-x)GeSe(4) (x = 0-0.1) are reported. The substitution of Zn(2+) with Cu(+) introduces holes as charge carriers in the system and results in an enhancement of the thermoelectric efficiency. Nano-sized impurities formed via phase segregation at higher dopant contents have been identified and are located at the grain boundaries of the material. The impurities lead to enhanced phonon scattering, a significant reduction in lattice thermal conductivity, and therefore an increase in the thermoelectric figure of merit in these materials. This study also reveals the existence of an insulator-to-metal transition at 450 K.

Enhanced thermoelectric performance through grain boundary engineering in quaternary chalcogenide Cu2ZnSnSe4

“…For a wide band gap semiconductor, the bipolar contribution to the total thermal conductivity can be omitted. 11,23 Therefore, the total thermal conductivity of CZTSe is combination of lattice and electronic contributions (κ=κ L + κ el ). By using the Wiedeman-Franz relation (κ el =LσT), the electronic contribution to the thermal conductivity can be estimated.…”

“…5,6 On the other hand, structural manipulations have been adopted to suppress the thermal conductivity, such as introducing nanoscale structures to reduce the phonon mean free path, point defect scattering through alloying with other elements, and lone pair electron to develop soft phonon modes. [7][8][9][10][11] As the thermoelectric transport characteristics depend on interrelated material properties, 4 simultaneous enhancement of the power factor and decrease of the thermal conductivity are challenging. 15 Besides, CZTSe nanocrystals with relatively low thermal conductivity showed that the maximum zT is 0.44 at 723K for CZTSe 16 and 0.7 at 723K for Cu 2.1 Zn 0.9 SnSe 4 .…”

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.…”

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

“…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 .…”