Interdiffusion
and solid–solid phase reaction
at the interface
between thermoelectric (TE) materials and the electrode critically
influence interfacial transport properties and the overall energy
conversion efficiency during service. Here, the microstructural evolution
and diffusion mechanisms at the interfaces between the most widely
used Bi2Te3-based TE materials, n-type Bi2Te2.7Se0.3 (BTS) and p-type Bi0.5Sb1.5Te3 (BST), and Ni electrodes were investigated
at atomic resolution using spherical aberration-corrected scanning
transmission electron microscopy (STEM). The BTS(0001)/Ni and BST(0001)/Ni
interfaces were constructed by depositing Ni nanoparticles on mechanically
exfoliated BTS and BST bulk materials and subsequent annealing. The
interfacial reaction is initially dominated by Ni diffusion into the
TE matrix to form NiAs-type NiM intermetallics, while Ni trans-quintuple-layer
diffusion only occurs in Sb-rich BST. The Bi-rich BTS is more influenced
by the Ni–Te preferential reaction, resulting in NiM abnormal
grain growth and the formation of tilted and rotated interfaces. Bi
diffusion into the BTS matrix forms a Bi double layer at the interface
or Bi2[Bi2(Te,Se)3] as the annealing
temperature increases, while Bi diffusion into the Ni thin film greatly
accelerates the interfacial reaction rate, as elucidated by in situ
heating STEM. The results provide essential structural details to
understand and prevent the degradation of TE device performance.