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 Ge0.94Bi0.05Te 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. The thermoelectric performance of rhombohedral GeTe-based material is boosted by the TiB2 nanoparticle-induced interfacial constraint effect that results in reduced equivalent deformation potential and substantial interfacial thermal resistance.