Recent Development of New Materials for Thermoelectric Applications

The increases in the ZT values are produced especially by the decrease in the thermal conductivity of crystal lattices, and the recent advances in the development of new TE materials are based on the search for mechanisms that make it possible to minimize the thermal conductivity in the crystal structures of TE materials. Advances in TE materials provide measurable improvements in ZT values through the use of nanotechnology-based techniques. Nanophonon metamaterials provide special local resonance states in semiconductor materials for suppression of thermal conductivity. According to Ouyang et al. [60], nascent theories are being forged in the field of TE materials. Among the most promising are the coherent phonon theories (https://www.nature.com/articles/nmat3826, aacessed on 23 August 2021), the nanophonon metamaterial [61], the rattling effect [62], the topological phonon [63,64] and the topological electron [65]. Likewise, the synthesis of low-dimensional materials would allow the separation of related thermoelectric parameters to optimize

thermoelectric performance. Among the advances in this field, the 1D Nanowires stand out [66,67], as well as the 2D Materials [68,69] and the Nanomesh Structures [70,71]. Finally, it should be noted that given the recent advances in computing, artificial intelligence and machine learning in combination with atomic simulation techniques, the development of new tools to predict new structures and characteristics of novel materials is envisioned, and these will provide accurate forecasts of the inherent properties of TE materials.

**Figure 5.** Research in thermoelectric materials in recent years.
