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[en] Highlights: • Bulk Cu2ZnSnSe4 materials are directly produced by combustion synthesis under gas pressure or high gravity. • Simultaneous densification is finished during synthesis to realize one-step preparation of dense samples. • By In-doping the Cu2ZnSn0.9In0.1Se4 sample shows an enhanced ZT of 0.59 at 773 K. Thermoelectric materials are attractive for solar thermal energy conversion and waste heat recovery. The preparation of bulk thermoelectric materials usually involves multi-step processes with considerable time and energy consumption. Here we report an alternative way called combustion synthesis to realize one-step and fast fabrication of bulk Cu2ZnSnSe4 thermoelectric materials. The combustion synthesis was carried out in 2 MPa Ar gas atmosphere or in a high-gravity field in order to reduce the porosity in samples and complete simultaneous densification during synthesis. Nearly full-dense Cu2ZnSnSe4 samples with a porosity of 2ZnSnSe4 materials prepared by other methods. The ZT of the Cu2ZnSnSe4 samples was clearly improved by partial substitution of Sn with In, and reached 0.59 at 773 K for the composition of Cu2ZnSn0.9In0.1Se4. Compared with the conventional melt growth and powder sintering methods, combustion synthesis offers a fast, one-step, and furnace-free way for directly producing bulk Cu2ZnSnSe4 samples, which may open up new possibilities for synthesis and applications of Cu2ZnSnSe4-based thermoelectric materials.
[en] Some group III elements such as Indium are known to produce the resonant impurity states in IV-VI compounds. The discovery of these impurity states has opened up new ways for engineering the thermoelectric properties of IV-VI compounds. In this work, resonant states in SnTe were studied by co-doping with both resonant (In) and extrinsic (Ag, I) dopants. A characteristic nonlinear relationship was observed between the Hall carrier concentration (n_H) and extrinsic dopant concentration (N_I, N_A_g) in the stabilization region, where a linear increase of dopant concentration does not lead to linear response in the measured n_H. Upon substituting extrinsic dopants beyond a certain amount, the n_H changed proportionally with additional dopants (Ag, I) (the doping region). The Seebeck coefficients are enhanced as the resonant impurity is introduced, whereas the use of extrinsic doping only induces minor changes. Modest zT enhancements are observed at lower temperatures, which lead to an increase in the average zT values over a broad range of temperatures (300–773 K). The improved average zT obtained through co-doping indicates the promise of fine carrier density control in maximizing the favorable effect of resonant levels for thermoelectric materials.
[en] Bulk In-doped Cu_2SnSe_3 samples were prepared by a fast and one-step method of high-gravity combustion synthesis. All the synthesized samples were dense with relative densities of >98%. The influence of Indium-doping on the phase composition of the samples was investigated. SEM and EDS measurements confirm the existence of SnSe and Cu_2Se as secondary phase in the Cu_2Sn_1_−_xIn_xSe_3 samples. In addition, the experimental results show that there is a solubility limit of indium in the Cu_2SnSe_3 matrix. The thermoelectric properties of the samples were measured in a temperature range from 323 K to 773 K, and the Cu_2Sn_0_._8In_0_._2Se_3 sample achieved a maximum ZT of 0.65 at 773 K, which was comparable with the best-reported result for Cu_2SnSe_3 materials prepared by conventional sintering approaches. With much reduced time and energy consumption, high-gravity combustion synthesis may offer a more efficient and economical way for producing thermoelectric materials. - Highlights: • Dense bulk Cu_2SnSe_3 materials are prepared by one-step combustion synthesis. • The solubility limit of Indium into the Cu_2SnSe_3 matrix has been discussed. • A maximum ZT of 0.65 is obtained for the Cu_2Sn_1_−_xIn_xSe_3 (x = 0.2) at 773 K.
[en] Highlights: • Thermoelectric performance of Nb-doped lead selenide was investigated. • Higher Seebeck coefficient was obtained in Nb-doped lead selenide. • The grain sizes are about 100-300 nm according to SEM. • There is little lattice thermal conductivity decrease. - Abstract: In present work, niobium is used as donor impurity in lead selenide to increase carrier concentration. Thermoelectric transport properties of n-type Pb1.04−xNbxSe are investigated from room temperature to 673 K. Higher Seebeck coefficient is reached by Nb-doping in lead selenide compared to other dopants. The Seebeck coefficient enhancement comes from band modification by Nb-doping, which results in the density of states effective mass increase. With the Seebeck coefficient enhancement, the dimensionless figure of merit ZT reaches ∼1.1 at 673 K
[en] A new type of quaternary selenide Ag_1_._7_5InSb_5_._7_5Se_1_1 has been synthesized. It crystallizes in the non-centrosymmetric space group Cm of monoclinic system, with a=13.419 (1) Å, b=4.084 (1) Å, and c=19.165 (2) Å, Z=2. The compound has a new three-dimensional layer structure which consists of infinite "2_∞[AgSb_2Se_4] layers and "2_∞[Ag1(Sb6)Ag3InSb_3Se_8] layers. The band gap of Ag_1_._7_5InSb_5_._7_5Se_1_1 is 0.94(2) eV, which agrees with its dark gray color. Moreover, the compound exhibits congruent-melting behavior. - Graphical abstract: Ag_1_._7_5InSb_5_._7_5Se_1_1 has a new three-dimensional layer structure which consists of infinite "2_∞[AgSb_2Se_4] layers and "2_∞[Ag1(Sb6)Ag3InSb_3Se_8] layers. - Highlights: • The new quaternary selenide Ag_1_._7_5InSb_5_._7_5Se_1_1 has been synthesized. • It crystallizes in non-centrosymmetric space group Cm and has a new layer structure. • The structure consists of "2_∞[AgSb_2Se_4] layers and "2_∞[Ag1(Sb6)Ag3InSb_3Se_8] layers. • The band gap of Ag_1_._7_5InSb_5_._7_5Se_1_1 is 0.94(2) eV. • The compound exhibits congruent-melting behavior