Enhanced thermoelectric performance and atomic-resolution interfacial structures in BiSbTe thermo-electro-magnetic nanocomposites incorporating magnetocaloric LaFeSi nanoparticles

Incorporating magnetic nanoparticles in thermoelectric (TE) materials introduce magnetic interfaces with additional electron and phonon scattering mechanism for high TE performance. However, the influence of heterogeneous interfaces between magnetic nanoparticles and TE matrix on electronic and thermal transport remains elusive in the thermo-electric-magnetic nanocomposites. Here, using p-type TE material Bi_0·3Sb_1·7Te₃ (BST) as matrix and magnetocaloric (MC) material La(Fe_0·92Co_0.08)_11.9Si_1.1 (LFS) nanoparticles as a second phase, TE/MC nanocomposites xLFS/BST (x = 0.1%, 0.2%, 0.3% and 0.4%) were synthesized using spark plasma sintering method. The atomic-resolution interfacial structures demonstrate that Te vacancies originating from LFS-BST interfacial reaction decreases the hole concentration of the LFS/BST nanocomposites and enhances the Seebeck coefficient. The LFS/BST nanocomposites exhibit lower thermal conductivity due to enhanced phonon scattering by interfaces and defects. All the nanocomposites have higher ZT than BST matrix, with 0.2%LFS/BST nanocomposite achieving highest ZT = 1.11 at 380 K. At working current 1.4 A, the device fabricated using 0.2%LFS/BST nanocomposite achieves maximal cooling temperature 4.9 K, which is 58% higher than the matrix. Moreover, the MC properties are retained in all the nanocomposites, which make them a promising candidate to achieve high TE performance and dual TE/MC properties for future applications.