Improving Thermoelectric Performance of n-Type Mg₃Bi₂-Based Materials by Introducing a Spatially Confined Magnetic Ordered Structure

Magnetism, which relates to the spin and orbital degrees of freedom, is recently considered as the fountain of some potentially paradigm-changing mechanisms to decouple the adversely interdependent thermal and electrical transport parameters of thermoelectric materials. Herein, we construct a thermo-electro-magnetic coupling thermoelectric system by introducing a spatially confined ferromagnetic CrTe secondary phase into the Mg 3.4 Bi 1.5 Sb 0.5 (MBA) matrix. It is found that the spatially confined magnetic ordered structure, CrTe, can act as electron injection units to substantially promote the carrier concentration of the MBA matrix without deteriorating the carrier mobility, which usually occurs in the uniform magnetic-element doping systems. An increase in the Seebeck coefficient of the CrTe-incorporated system due to the magnetic phase transition was also acknowledged, which further confirms the advantage of introducing spin and orbital degrees of freedom into the thermoelectric materials. Combined with the enhanced phonon scattering by the second phase, a maximum zT value ∼1.1 was achieved in the 0.35 wt % CrTe/Mg 3.4 Bi 1.5 Sb 0.5 composite at 587 K.