Giant Negative Compressibility in 2D Hybrid Perovskites via Configuration Transition and Rotation of Carbon Chains

Abstract Applying compressive force typically causes materials to shrink (or expand under tension). Materials that exhibit anomalous volume expansion upon compression (VEUC) present significant challenges and are the subject of extensively research. Here, it is discovered that (C ₈ H ₁₇ NH ₃ ) ₂ PbBr ₄ ( C8PbBr4 ), a 2D perovskite constructed by inorganic ‐[PbBr ₆ ]‐ connected by C chains , displays an abnormal volume expansion ratio of 12.9% under external compression. The giant VEUC results from the configurational change of C chains from initial parallel arrays to herringbone‐like arrays, accompanying with the rotation of C chains and the formation of tail‐to‐tail interaction in the herringbone‐like arrays due to a charge reinjection from chains to ‐[PbBr ₆ ]‐ , which subsequently expand the crystal lattice. These comparative experiments reveal that the VEUC in CnPbBr4 is chain length‐dependent, which is not obvious in those with C4‐ and C12‐chains. These findings on VEUC driven by configurational change of carbon chains open up a new avenue to explore synthetic materials with anomalous piezo‐mechanical properties for potential applications, such as smart body armors and artificial muscles.