Negative enthalpy delivers thermodynamically stable and high-performance GeTe thermoelectrics

Thermodynamic decomposition of thermoelectric (TE) materials is the core problem in TE power generation applications, which is the spontaneous result of lowering the system’s Gibbs free energy. Here, the negative-enthalpy strategy was proposed to improve both the thermodynamic stability and TE performance of GeTe-based materials. Multielement doping of negative mixing enthalpy elements at cation sites induces the local chemical ordering of atoms and vacancies, resulting in a stabilized lattice and an increased energy barrier for atomic diffusion. Meanwhile, the multiscale composition fluctuations dominated by the enthalpy-entropy competition provide the scattering for full-spectrum phonons, resulting in the ultralow lattice thermal conductivity and an exceptional zT of 2.7 at 800 K for the Ge 0.79 Mg 0.06 Cu 0.04 Sb 0.04 Pb 0.09 Te sample. Due to the improved thermodynamic stability and TE performance, a record-high experimental efficiency of 16% was achieved for the fabricated modules. This work provides valuable insights into the negative-enthalpy strategy for achieving thermodynamically stable and high-performance TE materials.