The First Ring Enlargement Induced Large Piezoelectric Response in a Polycrystalline Molecular Ferroelectric

Abstract Inorganic ferroelectrics have long dominated research and applications, taking advantage of high piezoelectric performance in bulk polycrystalline ceramic forms. Molecular ferroelectrics have attracted growing interest because of their environmental friendliness, easy processing, lightweight, and good biocompatibility, while realizing the considerable piezoelectricity in their bulk polycrystalline forms remains a great challenge. Herein, for the first time, through ring enlargement, a molecular ferroelectric 1‐azabicyclo[3.2.1]octonium perrhenate ([3.2.1‐abco]ReO4) with a large piezoelectric coefficient d 33 up to 118 pC/N in the polycrystalline pellet form is designed, which is higher than that of the parent 1‐azabicyclo[2.2.1]heptanium perrhenate ([2.2.1–abch]ReO4, 90 pC/N) and those of most molecular ferroelectrics in polycrystalline or even single crystal forms. The ring enlargement reduces the molecular strain for easier molecular deformation, which contributes to the higher piezoelectric response in [3.2.1‐abco]ReO4. This work opens up a new avenue for exploring high piezoelectric polycrystalline molecular ferroelectrics with great potential in piezoelectric applications.


The First Ring Enlargement Induced Large Piezoelectric Response in a Polycrystalline Molecular Ferroelectric
Yong Ai, Peng-Fei Li, Xiao-Gang Chen, Hui-Peng Lv, Yan-Ran Weng, Yu Shi, Feng Zhou, Ren-Gen Xiong* and Wei-Qiang Liao*        Compound 3. To an anhydrous toluene solution was dissolved Compound 2 (10.0 g, 41.1 mmol) and added t-BuOK (6.9 g, 61.7 mmol).The mixture was refluxed at 115°C for 4h.The mixture solution was cooled to room temperature, extracted with concentrated HCl (100 ml × 3).The aqueous phase was collected and refluxed at 110°C overnight.Then the saturated NaOH solution was added under ice bath until the pH > 8.The residue was extracted with ethyl acetate (100 mL × 5).The organic layer was collected, dried over with Na2SO4, filtered, and concentrated.The crude product of compound 3 was obtained as a light brown solid.GC-MS m/z (M + ): 125.10.1-Azabicyclo[3.2.1]octane.Compound 3 (10.0g, 80mmol) was dissolved in 30 ml hydrazine hydrate (98%) and refluxed at 120 ℃ for 8h.Then KOH (9.0 g, 160 mmol) and ethylene glycol (40 ml) was added.The mixture was refluxed at 160 ℃ overnight.The ethylene glycol was removed by reduced-pressure distillation.The residue was dissolved in 200 ml water and extracted with ethyl acetate (100 mL × 5).The organic layer was collected, dried over with Na2SO4, filtered, and concentrated.GC-MS shows the m/z (M + ) of 1-Azabicyclo[3.2.1]octane was 111.15.

Figure S1 .
Figure S1.The experimental PXRD patterns of [3.2.1-abco]ReO4 at room temperature, match well with the simulated PXRD patterns.

Figure S3 .
Figure S3.Packing view of crystal structure of [3.2.1-abco]ReO4 at 300 K, in which all the [3.2.1-abco] + cations are aligned in a head-to-tail manner along the longer body diagonal direction of the crystal cell.

Figure S5 .
Figure S5.A linear fit to the Curie−Weiss law using ε′ values at 1 MHz.

Figure S6 .
Figure S6.The SHG intensity of [3.2.1-abco]ReO4 compared to that of KDP at 300 K.