Suppressing lone-pair expression endows room-temperature cubic structure and high thermoelectric performance in GeTe-based materials

Abstract

The stereochemical expression of ns2 lone-pair electrons in specific Ⅳ-Ⅵ group semiconductors is pivotal to lattice instability, which induces ferroelectric phase transition. In the thermoelectric device working temperature range, the distinct change of thermal expansion coefficient, however, is introduced by phase transition and then severely restrains material's critical applications. Herein, taking the example of thermoelectric GeTe, the hidden role of manipulating lone pair expression to control the crystal structure is theoretically unraveled. Moreover, it is experimentally demonstrated that LiBiTe2-alloyed GeTe possess a room-temperature cubic structure and competitive thermoelectric performance. Density functional theory calculations reveal that reducing the charge orientation caused by the stereochemical activity of cation lone-pair electrons in GeTe is an effective strategy to achieve room-temperature cubic structure. LiBiTe2 is found to be a novel alloying agent to realize crystal structure manipulating, carrier concentration optimization, multi-band convergence, and lattice softening. Benefiting from the optimized electrical and thermal transport properties, an ultrahigh ZTave of 1.22 within 300–773 K in cubic (GeTe)0.80(LiBiTe2)0.20 is achieved. This work provides a new insight into manipulating lone pair expression to control crystal structure, and promotes the development and application of cubic GeTe-based materials.