Relaxor Ferroelectricity Enables Enhanced Thermoelectric Performance in In₂Se₃-Alloyed GeTe

The intuitive challenge in combining ferroelectric and thermoelectric materials lies in their diametrically opposed electrical conductivity requirements. As a narrow-band-gap semiconductor with spontaneous ferroelectric distortion, GeTe serves as an ideal paradigm for investigating the interplay between ferroelectricity and thermoelectricity, yielding novel strategies for synergistically optimizing the electrical and thermal transport properties of thermoelectric materials. In this work, a non-equimolar (2:3) In³⁺/Se^2- alloying strategy was implemented to deliberately introduce Ge vacancies in GeTe under an electrical neutrality condition. As a stronger perturbation to both lattice periodicity and local charge neutrality, Ge vacancies can effectively induce relaxor ferroelectricity in GeTe and thus broaden the temperature window of its minimum thermal conductivity. Combining the unique role of Ge vacancies in stabilizing the cubic phase of GeTe, a broadened temperature range of optimized electrical transport performance was simultaneously realized. Ultimately, a trade-off between electrical and thermal transport properties in an extended temperature range was achieved in (GeTe)_{1-2 x}(In₂Se₃)_x (x = 0.02-0.04) samples, yielding an optimized average zT value exceeding 1.0 within 330-625 K.