Capture of <i>B</i> 31‐Type MnSe _0.5 Te _0.5 Phase With Structure‐Borne Superconductivity Initiated by Pressure‐Induced Jahn–Teller Distortions

ABSTRACT Superconductivity in manganese‐based compounds is strongly dependent on their high‐pressure phases. Consequently, capturing high‐pressure superconducting phases, particularly those that cannot be crystallized in their bulk form at ambient condition yet retain superconductivity, is of significant interest. Here, we report the capture of a superconducting high‐pressure B 31‐type MnSe 0.5 Te 0.5 phase (space group Pnma ) at ambient pressure, achieved via chemical substitution‐induced irreversible phase transitions ( Fm m ⇀ P 6 3 / mmc ⇀ Pnma ) and reversible spin‐crossover under a hydrostatic compression‐decompression cycle up to ≈40 GPa. Upon decompression, the B 31 phase exhibits structure‐borne superconductivity that persists down to ≈4 GPa, with a maximum T c of ≈7.5 K at ≈8 GPa. DFT calculations reveal that the accumulated pressure‐induced charge transfer (ligand‐to‐Mn 2+ ) causes an abrupt Jahn–Teller distortion (JTD) in MnX 6 octahedra by lifting the t 2g orbital degeneracy in low‐spin Mn 2+ ( d 5 ). The JTD triggers Peierls‐like metallic Mn–Mn dimerization, facilitating electron‐pairing by driving local electron redistribution, thereby initiating superconductivity in the orthorhombic phase. These findings demonstrate an approach to retain a superconducting phase through chemical substitution‐induced irreversible phase transition under high‐pressure.