Thermoelectric (TE) materials have attracted widespread attention in the past few decades not only because of their excellent waste heat generation capability, but also in the solid-state refrigeration [1-4]. The SnT single crystal has a ZT value of 2.6, which is undoubtedly the best TE performance in current materials. As another member of the IV-VI semiconductor, SnTe is not only a lead-free material, but also has a crystal and band structure similar to PbTe crystal, and is considered to be one of the most promising thermoelectric materials. However, recent studies have shown that the ZT values of SNTE crystals are still very low because they themselves have a high thermal conductivity (typically greater than 2.5 Wm).
In this study, the researchers designed a simple, ultra-fast, green, high-yield microwave hydrothermal synthesis of nanoparticles (NPs). The directional adhesion growth mechanism and morphology control techniques are systematically discussed. In order to further verify and understand the nano-size effect, a SNTE reference sample was prepared by ball milling combined with spark plasma sintering (SPS).
Compared with the thermoelectric properties of pure SNTE bulk materials, the ultra-low thermal conductivity (1.5 W m). 1 K1 to 0.60 sm 1 K1, 323-800 K, relatively high Seebeck coefficient (58-90 μV K) found in NPs sintered samples with an average diameter of 165 nm, ZT value is higher (about 0.49 at 803K) This is related to enhanced phonon scattering and enhanced energy filtering effects.
Figure 1: (a) Microwave hydrothermal synthesis system: (b) Temperature profile as a function of reaction time, (c) XRD pattern of SNTE nanoparticles, (d) and (e) are SEM images at different magnifications, (f ) is an octahedral structure simulating SNTE nanoparticles; (g), (h), and (i) are global TEM, SEAD, and HRTEM images.
Figure 2: (a), (b) and (c) are SEM images of SnTe NPs synthesized with 0g, 1.0g, 1.25g NaOH; (d) are XRD patterns of samples (a) and (c); And (h), (f) and (i), (g) and (j) are SEM images of SNTE particles synthesized with 1.50 g, 2.50 g, 5.50 g NaOH.
Figure 3: (a) The overall morphology of the sample after SPS, the inlays are rectangular and square wafers, respectively, for testing thermoelectric properties and Hall measurements: (b) XRD patterns for undoped SNTE reference samples; c), (d), (e) and (f) are densified tests of sintering from mechanically alloyed powders (c) or particles of different diameters (165 nm (d), 550 nm (e) and 8.2 mm (f) Detailed SEM image on the sample.
Figure 4: Performance curves of dense samples sintered from 165 nm, 550 nm nanoparticles (NPs), 8.2 mm microparticles (MPS), and mechanical alloyed (MA) powders are: (a) Total thermal conductivity, (b ) lattice thermal conductivity, (c) electrical conductivity, (d) and (e) electrical transport mechanism, (f) hole mobility, carrier concentration and mmx*/0* ratio as a reduction in crystallites The function of size, (g) Seebeck coefficient, (h) power factor and (i) ZT value.