Raju Chetty

Selection of suitable electrical contact is crucial for achieving low specific contact resistivity ( ρ _c ) at the electrode/thermoelectric (TE) material interface. Sustaining low ρ _c is far more critical than merely attaining a low value. Moreover, the conversion efficiency ( η ) and durability are often limited by unstable contact interfaces at various junctions of the TE device and the thermal stability issues of commonly used metal contacts. To address these issues, two novel Cu‐based alloys, Brass (Cu–Zn) and Manganin (Cu–Ni–Mn), were developed in this work for high‐performance n‐type Mg ₃ (Sb, Bi) ₂ materials. These alloys were found to exhibit very low ρ _c < 5μΩ.cm ² , with limited diffusion to Mg ₃ (Sb, Bi) ₂ materials after optimizing the process parameters. Even though the ρ _c achieved after the conventional one‐step sintering was low, diffusion, inhomogeneity and thermal stability were shown to be bottlenecks. To solve this, a distinct two‐step contacting method was employed, and a process optimization was carried out to overcome the persisting issues and to stabilize the ρ _c and η . As a result of these strategies, a high maximum conversion efficiency of η _max ≈ 8.2% was achieved for Brass/Mg ₃ (Sb, Bi) ₂ /Brass contacts at Δ T ≈ 380 K, and showing no degradation after 15 days of thermal aging.

Mg ₃ Sb ₂ –Mg ₃ Bi ₂ solid‐solutions exhibit excellent thermoelectric (TE) performance in power generation and cooling. However, reports on fully Mg ₃ (Sb,Bi) ₂ ‐based TE devices remain limited, due to performance imbalance between p‐type and n‐type counterparts. In such cases, geometric design optimization is essential for achieving either a maximum power density (ω _max ) or maximum conversion efficiency (η _max ). Simultaneous improvement is often difficult due to compromises in the device fill factor. In this study, simultaneous enhancement of ω _max and η _max is demonstrated in a fully Mg ₃ Sb _1.5 Bi _0.5 device through optimized design. Two‐pair devices are fabricated using p‐ and n‐type doped Mg ₃ Sb _1.5 Bi _0.5 materials with Cu/Fe multilayer electrical contacts.The optimum cross‐sectional area ratio ( A _n / A _p ) is calculated using the constant properties model. Accordingly, a revised device architecture is designed to accommodate the optimum A _n / A _p = 1:2 without compromising the fill factor. Finite element simulations predict a combined improvement in ω _max and η _max compared to a non‐optimized 1:1 design. Simulations are experimentally validated with A _n / A _p = 1:1 and 1:2 devices, showing a“double‐high” improvement more than 10 % in ω _max and η _max at Δ T ≈465 K. The proposed optimization strategy provides a general approach to enhance both power output and conversion efficiency in various p‐n thermoelectric material combinations.

This study demonstrates the reduction of contact resistivity through the optimization of sintering temperatures, leading to a maximum conversion efficiency (η_max) of 9.3% at ΔT = 380 K for the SS_f/Mg₃Sb_1.5Bi_0.5/SS_f TE single leg with good stability.

By the fine manipulation of the exceptional long-range germanium-telluride (Ge─Te) bonding through charge transfer engineering, we have achieved exceptional thermoelectric (TE) and mechanical properties in lead-free GeTe. This chemical bonding mechanism along with a semiordered zigzag nanostructure generates a notable increase of the average zT to a record value of ~1.73 in the temperature range of 323 to 773 K with ultrahigh maximum zT ~ 2.7. In addition, we significantly enhanced the Vickers microhardness numbers ( H _v ) to an extraordinarily high value of 247 H _v and effectively eliminated the thermal expansion fluctuation at the phase transition, which was problematic for application, by the present charge transfer engineering process and concomitant formation of microstructures. We further fabricated a single-leg TE generator and obtained a conversion efficiency of ~13.4% at the temperature difference of 463 K on a commercial instrument, which is located at the pinnacle of TE conversion.

A facile route to fabricating a crack-free Mg_0.99Cu_0.01Ag_0.97Sb_0.99/graphene/PEDOT:PSS thermoelectric film on a flexible substrate.

Thermoelectric power generation from the prototype π-shaped module composed of p-type colusite (Cu₂₆Cr₂Ge₆S₃₂) and n-type nanostructured PbTe (Pb_0.98Ga_0.02Te-3% GeTe) was demonstrated in this study. The thermoelectric figure of merit zT of Cu₂₆Cr₂Ge₆S₃₂ and Pb_0.98Ga_0.02Te-3% GeTe was ∼0.8 and ∼1.2 at 665 K, respectively. In PbTe, transmission electron microscopic images and energy-dispersive x-ray elemental maps reveal the insertion of nanoscale precipitates induced by the GeTe alloying. Contact layers based on Au and Co-Fe were used for p- and n-type thermoelectric legs, respectively, which allow the low electrical specific contact resistances of ≤10 × 10⁻¹⁰ Ω m² at room temperature. Maximum thermoelectric conversion efficiency η_max of ∼5.5% was obtained for the Cu₂₆Cr₂Ge₆S₃₂ and Pb_0.98Ga_0.02Te-3% GeTe-based two-pair module when the hot-side T_h and cold-side T_c temperatures were maintained at 673 and 283 K, respectively. A three-dimensional finite-element simulation predicts the η_max of ∼7.1% for the module at T_h and T_c of 673 and 283 K, respectively.

Copper-based sulfides are promising materials for thermoelectric applications, which can convert waste heat into electricity. This study reports the enhanced thermoelectric performance of Cu₂₆V₂Ge₆S₃₂ colusite via substitution of antimony (Sb) for germanium (Ge) and introduction of copper (Cu) as an interstitial atom. The crystal structure of the solid solutions and Cu-rich compounds were analyzed by powder X-ray diffraction and scanning transmission electron microscopy. Both chemical approaches decrease the hole carrier concentration, which leads to a reduction in the electronic thermal conductivity while keeping the thermoelectric power factor at a high value. Furthermore, the interstitial Cu atoms act as phonon scatterers, thereby decreasing the lattice thermal conductivity. The combined effects increase the dimensionless thermoelectric figure of merit ZT from 0.3 (Cu₂₆V₂Ge₆S₃₂) to 0.8 (Cu₂₉V₂Ge₅SbS₃₂) at 673 K.