Enhanced Thermoelectric Performance of Nanostructured Bi2Te3 through Significant Phonon Scattering

Minority Carrier Blocking to Enhance the Thermoelectric Performance of Solution-Processed BixSb2-xTe3 Nanocomposites via a Liquid-Phase Sintering Process

Minority carrier blocking through heterointerface barriers has been theoretically proposed to enhance the thermoelectric figure of merit (ZT) of bismuth telluride based nanocomposites at elevated temperatures recently (Phys. Rev. B 2016, 93, 165209). Here, to experimentally realize the minority carrier blocking, a liquid-phase sintering process enabled by excess Te is applied to the solution-processed Bi_xSb_2-xTe₃ nanocomposites to introduce interfacial energy barriers. The controlling parameters in the liquid-phase sintering process such as the amount of excess Te, sintering temperature and holding time, and the Bi composition (x) are systemically tuned and investigated to fully understand the minority carrier blocking mechanism. These interface-engineering parameters are optimized for introducing maximum lattice imperfections and band-bending interfaces that are responsible for blocking the minority carrier and wide-range scattering of the phonons toward enhanced thermoelectric performance. High ZT > 1.4 at 375 K is realized in the Bi_0.5Sb_1.5Te₃ sample, which is much higher than those of the state-of-the-art commercial ingots (ZT ∼ 1) and other solution-processed nanocomposites. The enhanced ZT at elevated temperatures is mostly due to the suppression of bipolar thermal conductivity by minority carrier blocking as well as the reduction of lattice thermal conductivity. Adapting this solution synthesis process to design favorable heterointerfaces for minority carrier blocking in the liquid-phase sintering process holds promise to further enhance the ZT values.

Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe₂ substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10⁻²⁰–10⁻²³(m²/s), which is 10⁶~10⁷ and 10¹²~10¹³ times smaller than those of Ni [10⁻¹⁴–10⁻¹⁷(m²/s)] and Cu [10⁻⁸–10⁻¹¹(m²/s)] in Bi₂Te₃, respectively.

Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

Layered (Bi_1-xIn_x)₂Te₃-In₂Te₃ (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In₂Te₃ from a (Bi_1-xIn_x)₂Te₃ (x > 0.075) matrix. Employing solid state phase transformation, the Bi₂Te₃/In₂Te₃ interface density was tuned by modifying the driving force for In₂Te₃ precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi₂Te₃/In₂Te₃ interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi₂Te₃/In₂Te₃ interfaces and the interplay of bipolar transport in Bi₂Te₃. Significantly improved thermoelectric properties of Bi₂Te₃-In₂Te₃ composites as compared to the single phase (Bi_1-xIn_x)₂Te₃ solid solution are obtained.

A synergistic effect of metal iodide doping on the thermoelectric properties of Bi2Te3

The role of metal iodides on the thermoelectric properties of Bi₂Te₃ is investigated by conducting comparative studies of CuI, CsI and KI-doped Bi₂Te₃ analogs. The CuI dopant is superior to CsI and KI dopants in showing a larger power factor and lower lattice thermal conductivity.