Weakening electron-phonon coupling of GeTe by coexistence of cubic/rhombohedral phase via rationally rapid synthesis strategy

Abstract

Thermoelectric materials, which enable direct conversion of heat into electricity, have been widely investigated. Among these materials, GeTe-based compounds show great promise for thermoelectric applications. However, conventional synthesis methods struggle to preserve the high-performance cubic phase (C-GeTe) at room temperature and involve multiple time-consuming and energy-intensive steps such as long-time heating and annealing process. To address this problem, we developed a rapid synthesis strategy combining self-propagating high-temperature synthesis in vacuum-sealed tubes (SHS-V) and spark plasma sintering (SPS). Based on the non-equilibrium reaction process, we successfully realized the coexistence of the high-temperature cubic phase (C-GeTe) and the rhombohedral phase (R-GeTe) at room temperature for the first time, which weakened electron-phonon coupling in R-GeTe. The highly symmetric C-GeTe optimized carrier concentration while enhancing the density-of-states effective mass, significantly improving electrical transport properties. Simultaneously, the phase interfaces and fine grains formed during the rapid preparation process enhanced phonon scattering, reducing the lattice thermal conductivity. Ultimately, a comparable ZT value of 1.24 was achieved at 773 K. Such a rapid synthesis strategy can also be extended to other thermoelectric systems.