Molecular Ferroelectric Materials and Phase Transition Phenomena

Molecular ferroelectric materials comprise organic, organic–inorganic and framework systems that exhibit switchable spontaneous polarisation accompanied by reversible phase transitions. Distinguished by structural flexibility and chemical diversity, these materials enable precise control of polar order through molecular design, hydrogen bonding, proton transfer or orientational ordering of organic cations. Phase transition phenomena in such systems often involve symmetry‐breaking transformations between paraelectric and ferroelectric states, driven by temperature, electric field, pressure or light. The manifest coupling between molecular degrees of freedom and lattice distortions underpins their rich dielectric and electromechanical responses. Unique attributes such as low coercive fields, high piezoelectric coefficients and tunable optical activity make molecular ferroelectrics attractive for applications in memory devices, sensors, energy harvesting and nonlinear optics. Progress in crystal engineering has expanded the palette of polar phases, from one‐dimensional perovskite chains to two‐dimensional layered frameworks and metal–organic hosts, establishing a versatile platform for exploring multiaxial polarisation, improper coupling schemes and environmental compatibility.

Research from Nature Portfolio

Recent work on a quasi‐one‐dimensional organic–inorganic hybrid perovskite has achieved a spontaneous polarisation rivalling that of conventional inorganic ferroelectrics at room temperature, alongside a remarkably low coercive field and strong second harmonic generation response. First‐principles analysis revealed that the combined effects of a stereochemically active lone pair and ordered organic cations drive the enhanced polarisation, setting a new benchmark for molecular perovskites.

A group‐theoretical study of molecular perovskites has uncovered a wealth of improper ferroelectric coupling schemes arising from the inclusion of molecular units. This rational design paradigm demonstrates that hybrid substitutions vastly increase the number of pathways to acentric structures, offering direct synthetic handles for targeted polar functionality.

Investigations into proton tautomerism in solely organic ferroelectric crystals have shown record‐breaking spontaneous polarisation through cooperative proton transfer and π‐bond switching. By optimising domain wall mobility via thermal annealing and repetitive electrical pulsing, these systems achieve strong polarisation switching at low coercive fields, highlighting proton dynamics as a potent mechanism for high‐performance molecular ferroelectrics.

Molecular Ferroelectric Materials and Phase Transition Phenomena publication trend

The graph below shows the total number of articles in molecular ferroelectric materials and phase transition phenomena across all publications each year (not limited to Nature Index journals).

Technical terms

Ferroelectricity: The property of certain materials to exhibit a spontaneous electric polarisation that can be reversed by an external electric field.

Spontaneous polarisation: The net electric dipole moment per unit volume present in a ferroelectric material without the application of an external field.

Coercive field: The magnitude of the external electric field required to reverse the spontaneous polarisation in a ferroelectric material.

Improper ferroelectricity: A polar order arising indirectly through coupling to a non-polar primary structural distortion rather than as a fundamental lattice instability.

Piezoelectricity: The ability of a material to generate electric charge in response to applied mechanical stress and vice versa.

Curie temperature: The critical temperature above which a ferroelectric material transitions to a paraelectric phase and loses its polar order.

Phase transition: A transformation between different structural or polar states of a material, often involving symmetry changes driven by external stimuli.

References

1. Superior ferroelectricity and nonlinear optical response in a hybrid germanium iodide hexagonal perovskite. Nature Communications (2023).
2. The First Ring Enlargement Induced Large Piezoelectric Response in a Polycrystalline Molecular Ferroelectric. Advanced Science (2023).
3. Proton tautomerism for strong polarization switching. Nature Communications (2017).
4. Recipes for improper ferroelectricity in molecular perovskites. Nature Communications (2018).
5. Ferroelectric hybrid organic–inorganic perovskites and their structural and functional diversity. National Science Review (2022).