  The proximity effect at a highly transparent interface of an s-wave
superconductor (S) and a topological insulator (TI) provides a promising
platform to create Majorana zero modes in artificially designed
heterostructures. However, structural and chemical issues pertinent to such
interfaces are poorly explored so far. Here, we report the discovery of Pd
diffusion induced polarization at interfaces between superconductive
Pd$_{1+x}$(Bi$_{0.4}$Te$_{0.6}$)$_2$ (xPBT, $0\le x \le 1$) and Pd-intercalated
Bi$_2$Te$_3$ by using atomic-resolution scanning transmission electron
microscopy. Our quantitative image analysis reveals that nanoscale lattice
strain and QL polarity synergistically suppress and promote the Pd diffusion at
the normal and parallel interfaces, formed between Te-Pd-Bi triple layers (TLs)
and Te-Bi-Te-Bi-Te quintuple layers (QLs), respectively. Further, our
first-principles calculations unveil that the superconductivity of xPBT phase
and topological nature of Pd-intercalated Bi$_2$Te$_3$ phase are robust against
the broken inversion symmetry. These findings point out the necessity of
considering coexistence of electric polarization with superconductivity and
topology in such S-TI systems.
