Thermoelectric Properties of Compressed Titanium and Zirconium Trichalcogenides

We experimentally investigate the thermoelectric power (Seebeck effect) of quasi-two-dimensional single crystals of titanium and zirconium trichalcogenides (TiS3, ZrS3, ZrSe3, and ZrTe3) under applied high pressure up to 10 GPa. Both sulfides were characterized by n-type semiconducting conduction in the whole pressure range investigated and, generally, showed moderate pressure responses of their electronic properties. Metallic ZrTe3 conserved its p-type conduction under pressure, and its Seebeck coefficient curve displayed a distinct crossover near 2 GPa. Semiconducting ZrSe3 demonstrated more remarkable responses to applied pressure, which included a multiorder gradual drop in its electrical resistance value up to 9 GPa and an n–p inversion of the dominant conduction type around 6 GPa. Furthermore, we found that a thermoelectric power factor of ZrSe3 may be greatly improved under high applied pressure, achieving a value of an order of 3.5 mW/(K2 m) at 9.5 GPa. Thus, an appropriately strained p-type ZrSe3 with a dramatically reduced band gap value turns to be a promising thermoelectrics. One can anticipate that ZrSe3–ZrTe3 solid solutions, in which the addition of ZrTe3 should decrease the band gap value of ZrSe3 in a controlled manner, could also demonstrate high thermoelectric performance parameters. Reversibility and reproducibility of the pressure-driven changes in the electronic properties of ZrSe3 suggest that it has a potential for other industrial applications linked to cyclic stress loads, for example, in n–p switches or control of p–n–p transistor elements.