Record Enhancement of Curie Temperature in an Efficient Luminescent Hybrid Metal Halide Ferroelastic

ABSTRACT Ferroelastic materials with intrinsically switchable spontaneous strain hold great promise for actuators, shape‐memory systems, and energy‐harvesting technologies. However, enhancing the Curie temperature ( T c ) and multifunctionality remain long‐standing challenges in hybrid ferroelastics, as the former critically governs the operational temperature window while the latter paves the way for novel functionalities. Here, we present an organic–inorganic hybrid ferroelastic (4‐FPD) 2 KInCl 6 :Sb (4‐FPD = 4‐fluoropiperidinium), which showcases remarkable multifunctionality combining a high T c of 417 K with efficient red‐light emission. By implementing a fluorination strategy on the parent (piperidinium) 2 KInCl 6 ( T c = 263 K), we achieved a record enhancement of 154 K in T c for hybrid metal halide ferroelastics, far exceeding the reported enhancements induced by the isotope effect and other techniques. Moreover, strikingly, isovalent Sb 3+ doping into the inorganic framework introduces highly efficient radiative recombination centers within the lattice, which boosts the photoluminescence quantum yield of (4‐FPD) 2 KInCl 6 from 2.09% to 85.63% without compromising the intrinsic ferroelastic properties. This study offers an effective route for performance optimization and multifunctional design of hybrid ferroelastics.