Stereochemical Rearrangement of Functional Units in Pressurized Sn₄As₃ Superconductor

Understanding how matter changes under high pressure provides valuable insights into predicting the evolution of crystal structures and their associated physical properties. In layered SnAs-based compounds under pressure, such as Li0.6Sn2As2 and NaSnAs, a two-dimensional (2D) topotactic transition from trigonal SnAs3 to square SnAs4 has been proposed and verified, which leads to the better alignment of p-orbitals and enhanced superconductivity. In this study, we report a novel three-dimensional (3D) topotactic transition occurring in layered Sn4As3, in which a steric hindrance As layer is located between two adjacent SnAs3 layers. This structural transition from 2D to 3D can be understood as a stereochemical rearrangement of the transformed SnAs3–SnAs4 blocks. Due to the perfectly aligned p-orbitals in the orthogonal bonds of the Pm3̅m phase that facilitate electron hopping, the superconducting transition temperature (Tc) exceeds that of Li0.6Sn2As2 and sets a record among all reported SnAs-based compounds.