Lattice softening in thermoelectric materials

Lattice softening refers to reducing the lattice stiffness of materials by weakening the binding force between atoms, thereby changing the electron and phonon transport characteristics. The advantage of lattice softening compared to other strategies for optimizing the properties of thermoelectric materials is that it can significantly reduce the lattice thermal conductivity by reducing the sound velocity without significantly affecting the electrical properties. Moreover, lattice softening shows a wide range of application potential in other material fields, such as magnetostrictive materials and intermetallic alloys. However, systematic reviews on the causes, effects, and specific applications of lattice softening in thermoelectric materials are still limited. This review introduces the recent progress of lattice softening in thermoelectric materials, focusing on how to achieve it and its mechanism in optimizing thermoelectric performance. Through mechanical strain engineering, chemical doping, and phase transition strategies to achieve lattice softening, one could lower the phonon speed, reduce the lattice thermal conductivity, and optimize the Seebeck coefficient and conductivity. In the outlook section, the potential applications of lattice softening in sustainable energy technologies are explored.