Ren-Gen Xiong

Domino‐like phase transitions offer a powerful route to propagate structural changes through local stimuli, yet their coupling with ferroelectricity in molecular materials has remained elusive. Here we show that water enables a domino‐like phase transition in the hybrid copper halide Gua ₃ Cu ₂ I ₅ (Gua ⁺ = CN ₃ H ₆ ⁺ ), providing non‐thermal access to a polar molecular ferroelectric. We find that the polar α phase cannot be reached through conventional thermal pathways but instead emerges through a hierarchical transition mechanism. In this mechanism, water first induces a surface solid–liquid–solid conversion via localized dissolution and reprecipitation, which subsequently triggers an interface‐propagated domino‐like transformation from the non‐polar β phase into the ferroelectric α phase in the bulk. This process can be directly visualized through real‐time luminescence contrast and is accompanied by robust, switchable ferroelectric polarization at room temperature. By identifying water as an active mediator rather than a passive environment, our results establish a new pathway for accessing polar phases beyond thermal equilibrium and provide a conceptual framework for coupling domino‐like phase transitions with ferroelectric functionality in molecular materials.

ABX₃-type perovskites and metal-organic frameworks (MOFs) have attracted sustained scientific interest due to their rich functionalities. However, the convergence of these two families, where MOFs adopt the perovskite architecture incorporating neutral X-sites, remains largely unexplored. Moreover, self-healing is notable for its ability to recover from damage, while achieving self-healing in molecular crystals remains a significant challenge. Herein, for the first time, we report a self-healing neutral X-site perovskite ferroelastic crystal (SbF₆)Ag(pyrazine)₃, in which the neutral pyrazine acts as the X-site, in contrast to the anion X-site in conventional perovskites. It undergoes reconstructive mm2Fm-type ferroelastic phase transition at 163 K and order-disorder 4̅3mFmm2-type ferroelastic phase transition at 322 K. Intriguingly, the reconstructive transition involves reversible breaking of Ag⁺-N coordination bonds and the formation of weak Ag⁺···π interactions, which unlocks the self-healing property, distinct from previous reported self-healing mechanisms in molecular crystals. The low-temperature reconstructive transition generates a spontaneous strain nearly ten times larger than that of the high-temperature transition, leading to crystal microcracks that are subsequently healed upon reversible phase recovery. Our discovery opens up a novel strategy to realize self-healing in molecular crystals and demonstrates the neutral X-site ABX₃-type perovskites as a fertile ground for multifunctional materials.

ABX ₃ ‐type perovskite materials have garnered significant and sustained attention over the years owing to their diverse functional properties and chemical versatility. This class encompasses inorganic oxides, organic–inorganic hybrids, and emerging metal‐free variants. However, it is noteworthy that nearly all perovskite materials developed thus far are constituted exclusively of ionic components occupying the A‐, B‐, and X‐sites. Here, we introduce a new class of three‐dimensional ABX ₃ perovskites with a neutral molecule as the X‐site, exemplified by (PF ₆ )Na(1,4‐dioxane) ₃ and (ClO ₄ )Ag(1,4‐dioxane) ₃ . Neutral 1,4‐dioxane molecules coordinate with monovalent B‐site metal cations to form corner‐sharing B(1,4‐dioxane) ₆ octahedra, generating positively charged three‐dimensional frameworks that encapsulate spherical A‐site counter‐anions. Specifically, (PF ₆ )Na(1,4‐dioxane) ₃ undergoes a 4/ mmm F2/ m ferroelastic transition at 290 K. Meanwhile, (ClO ₄ )Ag(1,4‐dioxane) ₃ exhibits successive m m F4/ mmm and 4/ mmm F2/ m ferroelastic transitions at 302 and 292 K, accompanied by clearly observable stripe‐like ferroelastic domains and switchable birefringence. Notably, constructing ABX ₃ perovskites with a neutral X‐site enables stable 3D frameworks within the Goldschmidt tolerance criteria and greatly expands chemical flexibility, allowing precise modulating of structural and functional properties. The introduction of this fundamentally new perovskite subclass opens up vast possibilities for achieving exotic properties and functionalities, further enriching this highly promising material platform.

ABX ₃ ‐type perovskite materials have garnered significant and sustained attention over the years owing to their diverse functional properties and chemical versatility. This class encompasses inorganic oxides, organic–inorganic hybrids, and emerging metal‐free variants. However, it is noteworthy that nearly all perovskite materials developed thus far are constituted exclusively of ionic components occupying the A‐, B‐, and X‐sites. Here, we introduce a new class of three‐dimensional ABX ₃ perovskites with a neutral molecule as the X‐site, exemplified by (PF ₆ )Na(1,4‐dioxane) ₃ and (ClO ₄ )Ag(1,4‐dioxane) ₃ . Neutral 1,4‐dioxane molecules coordinate with monovalent B‐site metal cations to form corner‐sharing B(1,4‐dioxane) ₆ octahedra, generating positively charged three‐dimensional frameworks that encapsulate spherical A‐site counter‐anions. Specifically, (PF ₆ )Na(1,4‐dioxane) ₃ undergoes a 4/ mmm F2/ m ferroelastic transition at 290 K. Meanwhile, (ClO ₄ )Ag(1,4‐dioxane) ₃ exhibits successive m m F4/ mmm and 4/ mmm F2/ m ferroelastic transitions at 302 and 292 K, accompanied by clearly observable stripe‐like ferroelastic domains and switchable birefringence. Notably, constructing ABX ₃ perovskites with a neutral X‐site enables stable 3D frameworks within the Goldschmidt tolerance criteria and greatly expands chemical flexibility, allowing precise modulating of structural and functional properties. The introduction of this fundamentally new perovskite subclass opens up vast possibilities for achieving exotic properties and functionalities, further enriching this highly promising material platform.

Ferroelectrics and clusters have independently attracted significant attention as two important classes of functional materials. Bridging these two fields by introducing ferroelectricity into clusters offers a compelling strategy to overcome the intrinsic limitations of conventional small-molecule materials. However, cluster-based ferroelectrics remain exceedingly rare and challenging to realize. In this study, we report the construction of an organosilicon molecular cluster ferroelectric, aminopropyl isobutyl Si8O12 cluster (1), achieved by introducing distorted tetrahedral units with a polar –NH2 group. Crystal 1 undergoes a 3F1-type ferroelectric-ferroelastic phase transition at 328 K, accompanied by a distinct on/off switching behavior of optical birefringence. Comprehensive structural and physical characterizations confirm the coexistence of ferroelectricity and ferroelasticity. Remarkably, this multiferroic crystal demonstrates excellent thermal stability, high chemical robustness, a large number of polar axes, pronounced entropy change, and a low elastic modulus compared with previously reported organosilicon ferroelectric crystals. To the best of our knowledge, Crystal 1 is the first organosilicon cluster ferroelectric, establishing a new design paradigm for organosilicon and molecular ferroelectrics.

The realization of pure out‐of‐plane polarization in ferroelectric thin films is crucial for next‐generation high‐performance microelectronics and miniaturized devices. Molecular ferroelectrics, which allow facile and large‐area thin‐film fabrication via solution processing, have gained tremendous attention in recent years. However, to date, molecular ferroelectric thin films with pure out‐of‐plane polarization have never been reported due to the inconsistency of their random orientation with the polarization direction. Herein, 3D chiral alkali metal halide ferroelectrics R / S ‐AQCsI ₃ (AQ = 3‐aminoquinolinium) are designed, of which thin films exhibit a highly preferred (00 l ) orientation. Notably, R / S ‐AQCsI ₃ can undergo an unprecedented reconstructive phase transition from hybrid 3D perovskitoid to perovskite structure while maintaining the thin films with the (00 l ) preferential orientation. More importantly, such a topological rearrangement of the 3D inorganic [CsI ₃ ] _n ²⁻ framework triggers chiral AQ ²⁺ cation reorientation in the lattice, which changes the polarization direction from b ‐axis in the polar perovskitoid phase to c ‐axis in the perovskite phase, enabling the variation from pure in‐plane to pure out‐of‐plane polarization in the thin‐film. To the knowledge, this is the first report of molecular ferroelectric thin films with pure out‐of‐plane polarization. This work opens up an avenue for achieving pure out‐of‐plane polarization in molecular ferroelectric thin films.

Crown ether compounds have garnered significant research interest for decades due to their unique host-guest supramolecular structure and various properties, such as ferroelectricity. However, although many crown ether derivatives have been developed, only the classical crown ether represented by 18-crown-6 was used as the host for crown ether host-guest-type ferroelectrics, and the heterocrown ether-based ferroelectrics have never been reported. Here, for the first time, we propose the strategy of asymmetric coordination through heterocrown ether as a host molecule to unlock ferroelectricity in metal-crown host-guest assemblies. Compared to the symmetrical coordination of the parent M(NO₃)₂(18-crown-6) (M = Pb²⁺ or Cd²⁺), an asymmetric coordination environment for the M²⁺ ion was created in M(NO₃)₂(1-aza-18-crown-6), enabling precise symmetry breaking and inducing ferroelectricity. Remarkably, Pb(NO₃)₂(1-aza-18-crown-6) exhibits an ultrahigh T_c of 470 K, which represents the maximum value reported to date for crown ether-based ferroelectrics. Such high T_c originates from the synergistic effect of disordered rotation commonly observed in the host-guest compounds and the unique out-of-plane flipping motion of the -NH- group in aza-crown ether. To the best of our knowledge, M(NO₃)₂(1-aza-18-crown-6) represents the birth of the first heterocrown ether ferroelectric family. Our findings provide a new way to design crown ether host-guest ferroelectrics with high performance and greatly stimulate the further exploration of heterocrown ether ferroelectrics.

Ferroelectric crystals possess essential properties for a wide array of applications, while their inherent brittleness presents significant challenges in smart scenarios that demand high flexibility and customizable shapes. Herein, an aminoborane adduct ferroelectric molecular crystal, trimethylamine chloroborane (TMACB), is synthesized, showing room‐temperature metal‐like malleability and ductility. TMACB crystallizes in rhombohedral R 3 m space group at room temperature and undergoes structural phase transition to monoclinic Cc space group at 256 K. The compressive strain of TMACB single crystal can reach ≈94% before fracture, more than 16 times that of traditional inorganic ferroelectrics (less than 6% in general), and large ultimate tensile strain of 15.6% can also be achieved. Both polarization‐electric field hysteresis loop and piezoresponse force microscopy characterizations have demonstrated ferroelectricity of TMACB, which is further firmly supported by density functional theory calculation. Moreover, compressed thin sheet of TMACB crystal maintains promising ferroelectric performance with a large polarization value of 23.9 microcoulomb per square centimeter, close to that of inorganic ferroelectric BaTiO ₃ . The discovery breaks through the research paradigm of brittle ferroelectric materials and offers new insights into the exploration of highly deformable ferroelectric crystals for flexible wearable devices and adaptable sensor arrays in the future.

Molecule intercalation has shown distinct advantages in modulating the superconducting properties of 2D materials. Chiral molecule intercalation provides a strategy for tuning electronic properties, while this approach has been limited to a few 2D materials such as TaS₂ and TiS₂. Although extensive research on 2D SnSe₂ exists, chiral molecule intercalation in SnSe₂ remains unexplored. Herein, we report the first successful electrochemical intercalation of chiral CTA cations (CTA = 3-chloro-2-hydroxypropyltrimethylammonium) into SnSe₂ by using piezoelectric R/S-CTA-Cl with a large piezoelectric coefficient of approximately 24 pm/V as the precursors, leading to the formation of superconductors R/S-CTA–SnSe₂. Characterization techniques, including powder X-ray diffraction, Raman spectroscopy, and circular dichroism spectroscopy, confirm a significant lattice expansion in SnSe₂ and the successful intercalation of chiral CTA cations, while polar R/S-CTA-Cl does not endow R/S-CTA–SnSe₂ with piezoelectric/ferroelectric properties. Magnetic susceptibility and electrical transport measurements reveal that the intercalated R/S-CTA–SnSe₂ materials exhibit a superconducting transition at around 5 K. Notably, the distinct out-of-plane and in-plane upper critical magnetic fields demonstrate the 2D nature of the intercalated compounds. This work highlights an approach for designing and tailoring superconducting materials through chiral cation intercalation and opens avenues for further exploration of chiral effects in superconductors.