Selective Dissolution-Derived Nanoporous Design of Impurity-Free Bi2 Te3 Alloys with High Thermoelectric Performance.

Thermoelectric technology, which has been receiving attention as a sustainable energy source, has limited applications because of its relatively low conversion efficiency. To broaden their application scope, thermoelectric materials require a high dimensionless figure of merit (ZT). Porous structuring of a thermoelectric material is a promising approach to enhance ZT by reducing its thermal conductivity. However, nanopores do not form in thermoelectric materials in a straightforward manner; impurities are also likely to be present in thermoelectric materials. Here, a simple but effective way to synthesize impurity-free nanoporous Bi0.4 Sb1.6 Te3 via the use of nanoporous raw powder, which is scalably formed by the selective dissolution of KCl after collision between Bi0.4 Sb1.6 Te3 and KCl powders, is proposed. This approach creates abundant nanopores, which effectively scatter phonons, thereby reducing the lattice thermal conductivity by 33% from 0.55 to 0.37 W m-1 K-1 . Benefitting from the optimized porous structure, porous Bi0.4 Sb1.6 Te3 achieves a high ZT of 1.41 in the temperature range of 333-373 K, and an excellent average ZT of 1.34 over a wide temperature range of 298-473 K. This study provides a facile and scalable method for developing high thermoelectric performance Bi2 Te3 -based alloys that can be further applied to other thermoelectric materials.

Atomic Layer Growth of Rutile TiO2 Films with Ultrahigh Dielectric Constants via Crystal Orientation Engineering.

In general, the electronic and optical properties of oxide films can significantly benefit from highly textured crystallinity. However, oxide films grown by atomic layer deposition (ALD), a powerful technique for the synthesis of high-quality, nanoscale thin films, usually exhibit amorphous or randomly oriented polycrystalline phases. Here, we demonstrate the growth of highly textured rutile phase ALD TiO2 films through rational substrate design. Both a- and c-axis preferentially oriented TiO2 films are obtained by varying the lattice parameters of the initial ALD growth surface. Under optimized conditions, we find that it is possible to deposit high-quality, c-axis preferentially aligned TiO2 films with a bulk dielectric constant approaching 185, rivaling the single crystal limit. These films display a remarkably high dielectric constant of 117 despite thin thickness of 5.2 nm. Moreover, the addition of a single doping sequence of Al2O3 successfully suppresses leakage currents to levels compatible with modern dynamic random access memory cells, all the while maintaining the high bulk dielectric constant of 137. These results clearly highlight the prospect of utilizing crystal orientation engineering in ALD thin films for emerging semiconductor devices.

Unlocking the Potential of Porous Bi2Te3-Based Thermoelectrics Using Precise Interface Engineering through Atomic Layer Deposition.

Porous thermoelectric materials offer exciting prospects for improving the thermoelectric performance by significantly reducing the thermal conductivity. Nevertheless, porous structures are affected by issues, including restricted enhancements in performance attributed to decreased electronic conductivity and degraded mechanical strength. This study introduces an innovative strategy for overcoming these challenges using porous Bi0.4Sb1.6Te3 (BST) by combining porous structuring and interface engineering via atomic layer deposition (ALD). Porous BST powder was produced by selectively dissolving KCl in a milled mixture of BST and KCl; the interfaces were engineered by coating ZnO films through ALD. This novel architecture remarkably reduced the thermal conductivity owing to the presence of several nanopores and ZnO/BST heterointerfaces, promoting efficient phonon scattering. Additionally, the ZnO coating mitigated the high resistivity associated with the porous structure, resulting in an improved power factor. Consequently, the ZnO-coated porous BST demonstrated a remarkable enhancement in thermoelectric efficiency, with a maximum zT of approximately 1.53 in the temperature range of 333-353 K, and a zT of 1.44 at 298 K. Furthermore, this approach plays a significant role in enhancing the mechanical strength, effectively mitigating a critical limitation of porous structures. These findings open new avenues for the development of advanced porous thermoelectric materials and highlight their potential for precise interface engineering through the ALD.