High zT and Its Origin in Sb-doped GeTe Single Crystals.

A record high zT of 2.2 at 740 K is reported in Ge0.92Sb0.08Te single crystals, with an optimal hole carrier concentration ≈4 × 1020 cm-3 that simultaneously maximizes the power factor (PF) ≈56 µW cm-1 K-2 and minimizes the thermal conductivity ≈1.9 Wm-1 K-1. In addition to the presence of herringbone domains and stacking faults, the Ge0.92Sb0.08Te exhibits significant modification to phonon dispersion with an extra phonon excitation around ≈5-6 meV at Γ point of the Brillouin zone as confirmed through inelastic neutron scattering (INS) measurements. Density functional theory (DFT) confirmed this phonon excitation, and predicted another higher energy phonon excitation ≈12-13 meV at W point. These phonon excitations collectively increase the number of phonon decay channels leading to softening of phonon frequencies such that a three-phonon process is dominant in Ge0.92Sb0.08Te, in contrast to a dominant four-phonon process in pristine GeTe, highlighting the importance of phonon engineering approaches to improving thermoelectric (TE) performance.

Interfacial Stability in Bi2Te3 Thermoelectric Joints.

Bismuth telluride (Bi2Te3)-based thermoelectric materials are well-known for their high figure-of-merit (zT value) in the low-temperature region. Stable joints in the module are essential for creating a reliable device for long-term applications. This study used electroless Co-P to prevent a severe interfacial reaction between the joints of solder and Bi2Te3. A thick and brittle SnTe intermetallic compound layer was successfully inhibited. The strength of the joints improved, and the fracture mode became more ductile; furthermore, there was no significant degradation of thermoelectric properties after depositing the Co-P layer after long-term aging. The result suggests that electroless Co-P could enhance the interfacial stability of the joints and be an effective diffusion barrier for Bi2Te3 thermoelectric modules.

Engineering Nanostructural Routes for Enhancing Thermoelectric Performance: Bulk to Nanoscale.

Thermoelectricity is a very important phenomenon, especially its significance in heat-electricity conversion. If thermoelectric devices can be effectively applied to the recovery of the renewable energies, such as waste heat and solar energy, the energy shortage, and global warming issues may be greatly relieved. This review focusses recent developments on the thermoelectric performance of a low-dimensional material, bulk nanostructured materials, conventional bulk materials etc. Particular emphasis is given on, how the nanostructure in nanostructured composites, confinement effects in one-dimensional nanowires and doping effects in conventional bulk composites plays an important role in ZT enhancement.