Giant ZT enhancement in rhombohedral GeTe-based thermoelectric materials

The peak figure of merit (ZT) of GeTe-based thermoelectric (TE) materials is typically attained in the high-temperature cubic phase, where the inevitable phase transition raises concerns over interfacial instability during operation. Therefore, developing high-performance rhombohedral GeTe below the phase transition temperature represents a more viable path toward practical applications. Herein, we propose a facile nanocomposite strategy to enhance the TE performance of rhombohedral GeTe by incorporating high-modulus TiB₂ nanoparticles into Ge_0.94Bi_0.05Te matrix. We demonstrate that the nanoparticle-induced interfacial constraint effect contributes to increasing longitudinal elastic modulus and decreasing equivalent deformation potential, accounting for improved carrier mobility. Additionally, these TiB₂ inclusions form heterogeneous interfaces that promote charge depletion and generate substantial thermal resistance, concurrently suppressing the heat transfer by carriers and phonons. Consequently, an extraordinary ZT of 2.66 at 613 K and a superior average ZT of 1.29 (300 ~ 613 K) are obtained in the rhombohedral GeTe-based composite. This work shows a paradigm for synergistically optimizing the electrical and thermal transports of emerging TE systems with nanoinclusions.