Simultaneous enhancement of power factor and suppression of thermal conductivity in bulk TlFe 1.6 Se 2 via embedded atomically thin FeSe layers
Year: 2026
Type: article
Abstract: FeSe in the monolayer limit exhibits extremely large thermoelectric power factors (PF). Extending the high-PF concept from two-dimensional FeSe to bulk materials, together with lattice thermal conductivity suppression, enables higher-performance thermoelectrics. Here, layered TlFe1.6Se2 is identified as a model system consisting of atomically thin two-dimensional FeSe layers separated by Tl atoms; i.e., FeSe monolayers are naturally confined within a bulk crystal. This compound uniquely exhibits a transition from Fe-vacancy (VFe)-ordered to -disordered states around 200 °C. Although VFe-disordered phase exhibits high electrical conductivity, carrier compensation suppresses Seebeck coefficient and limits PF. In contrast, VFe-ordered phase shows an enhanced Seebeck coefficient associated with Mott gap formation, resulting in improved PF much higher than that of bulk FeSe. The lattice thermal conductivity of VFe-ordered phase is lower than those of representative thermoelectric chalcogenides, and that of VFe-disordered phase further decreases to ~0.2 W/(m·K) at 500 °C due to VFe-induced bond heterogeneity. Consequently, the dimensionless figure of merit (ZT) of TlFe1.6Se2 reaches ~0.2 at 50 °C in VFe-ordered phase, which is two orders of magnitude higher than bulk FeSe. These results demonstrate that confining FeSe monolayers within a bulk crystal, alongside vacancy order–disorder control, is an effective design strategy for next-generation thermoelectrics.
DOI: 10.48505/nims.6393
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7168414624