A Molecular Polycrystalline Ferroelectric with Record-High Phase Transition Temperature

An outstanding advantage of inorganic ceramic ferroelectrics is their usability in the polycrystalline ceramic or thin film forms, which has dominated applications in the ferroelectric, dielectric, and piezoelectric fields. Although the history of ferroelectrics began with the molecular ferroelectric Rochelle salt in 1921, so far there have been very few molecular ferroelectrics, with lightweight, flexible, low-cost, and biocompatible superior properties compared to inorganic ceramic ferroelectrics, that can be applied in the polycrystalline form. Here, a multiaxial molecular ferroelectric, guanidinium perchlorate ([C(NH₂)₃]ClO₄), with a record-high phase transition temperature of 454 K is presented. It is the rectangular polarization–electric field (P–E) hysteresis loops recorded on the powder and thin film samples (with respective large P_r of 5.1 and 8.1 µC cm⁻²) that confirm the ferroelectricity of [C(NH₂)₃]ClO₄ in the polycrystalline states. Intriguingly, after poling, the piezoelectric coefficient (d₃₃) of the powder sample shows a significant increase from 0 to 10 pC N⁻¹, comparable to that of LiNbO₃ single crystal (8 pC N⁻¹). This is the first time that such a phenomenon has been observed in molecular ferroelectrics, indicating the great potential of molecular ferroelectrics being used in the polycrystalline form like inorganic ferroelectrics, as well as being viable alternatives or supplements to conventional ceramic ferroelectrics.

Guanidinium perchlorate is found to show multiaxial ferroelectricity with extremly low coercive field. Its polycrystalline samples show properties similar to those in ceramic ferroelectrics, such as switchable polarization and piezoelectric coefficient for the powder-pressed plates.

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