Role of Cation Vacancies in Cu₂SnSe₃ Thermoelectrics

Abstract

In this study, a series of Cu2–x SnSe3 (x = 0.075–0.175) and Cu2Sn1–y Se3 (y = 0.06–0.1) compounds were synthesized by self-propagating high-temperature synthesis combined with plasma-activated sintering. The effects of different cation vacancies (Cu vacancies and Sn vacancies) on the thermoelectric properties are systematically studied. Both Cu vacancies and Sn vacancies enhance the carrier densities and move the Fermi level deeply into the valence band, promoting the multiband from Γ and S points involved in the electrical transport and increasing the effective mass, which is further corroborated by the theoretical calculation. Due to the stronger carrier scattering caused by Cu vacancies, the mobilities of samples with Cu deficiencies reduce leading to decreased power factors. The power factors of samples with Sn deficiencies increase owing to the increased carrier concentration and attaining a maximum power factor of 10.17 μW cm–1 K–2 at 800 K. Besides, the deficiencies of both Cu and Sn strengthen the phonon scattering, and samples with Cu deficiencies obtain lower thermal conductivity than samples with Sn deficiencies due to the lower electronic thermal conductivity. All the samples with cation deficiencies have improved thermoelectric properties. For Cu1.875SnSe3, ZT reaches 0.95 at 800 K, which is 83% higher than those of undoped samples, while for Cu2Sn0.93Se3, ZT reaches 0.87 at 800 K, which is a 67% improvement.

Energy Conversion Processes with Perovskite-type Materials

“…The model samples produced by intentionally 8 depositing an oxyhydroxide phase on different supports suggests that perovskite-type oxides, which are ultimately able to build-up an active oxyhydroxide layer, are not barely a precursor of the active phase (the oxyhydroxide) but play also an essential role in boosting and sustaining the OER activity. [13] The same study also highlights the importance of the Fe presence in the self-assembled oxyhydroxide layer, being Co-or FeO(OH) catalysts much less active than the Co/FeO(OH) one. [13] Therefore, we have also carried out a systematic study to understand the functional role of Fe in perovskite OER catalysts with respect to activity and stability under operating conditions.…”

“…[13] The same study also highlights the importance of the Fe presence in the self-assembled oxyhydroxide layer, being Co-or FeO(OH) catalysts much less active than the Co/FeO(OH) one. [13] Therefore, we have also carried out a systematic study to understand the functional role of Fe in perovskite OER catalysts with respect to activity and stability under operating conditions. [11c] In perovskite-type oxides as BSCF or LSCF, despite the fact that Fe constitutes only ⁓5 wt% of the mixed oxide, it greatly boosts both OER activity and stability performance.…”

“…In a recent study [13] we have deliberately produced Co/Fe oxyhydroxide layers on the surface of different supports, such as amorphous carbon and perovskite-type oxides. The study shows that an interplay between the oxyhydroxide and the support occurs, and particularly only perovskite supports with large oxygen vacancy content, e.g.…”

Defects Engineering with Multiple Dimensions in Thermoelectric Materials

“…In accordance with the downshift Fermi level, the increased carrier concentration is observed and multiband around the downshift Fermi level can be involved in the electrical transportation. In Cu 2 Sn 0.93 Se 3 , ZT value of 0.87 is achieved at 800 K which is 67% higher than the pristine sample [63]. Except for moving the position of the Fermi level, the point defects may induce impurity levels contributing to an optimization of electrical [46].…”

Existence of Partially Degenerate Electrical Transport in Intermetallic Cu2SnSe3 Thermoelectric System Sintered at Different Temperatures

“…Previous studies on the band structure calculations have revealed that they have narrow band gap in the range 0.1-1.7 eV [4][5][6]. Various attempts have been done to enhance the TE performance via modifying electron and phonon transports through doping, non-stoichiometry and composites [1,[7][8][9]. Different methods like conventional solid-state reaction [8], fast combustion synthesis [10], liquid phase reactive sintering [6], spark plasma sintering [11], direct fusion of precursors [12], melt quenching [4] have been tried for synthesis of good quality bulk Cu 2 SnSe 3 polycrystalline materials.…”