Piezoelectric Multicomponent crystal Discs of R-(-)-Mandelic Acid with High Force Sensitivity

Over the years, there has been an ever-growing interest in organic piezoelectric materials as alternatives to traditional inorganic piezoelectrics due to environmental concerns, complicated synthetic protocols, and limited structure-property control. While quite prevalent among organic materials, owing to the existence of diverse families of non-centrosymmetric organic materials, multicomponent crystals (MCCs) offer the possibility of creating novel libraries of materials with controlled structure and properties. Herein, we report three new MCCs, namely, R-Mand•L-Lys•H2O (1), R-Mand•L-Hist (2), R-Mand•Bz•H2O (3), by cocrystallisation of R-(─)-Mandelic acid (R-Mand) with L-Lysine (L-Lys), L-Histidine (L-Hist) and benzimidazole (Bz), respectively. Considerable piezoelectric responses are calculated for all three MCCs using Density Functional Theory (DFT), with a maximum predicted value of 9.41 pC/N. Particularly, MCC 1 and 2, both fabricated into standalone polycrystalline discs with improved handleability, exhibit average macroscopic piezoresponse of 2.04 pC/N and 0.40 pC/N, respectively, exceeding their corresponding DFT-predicted d33 responses. The comparable single crystal longitudinal piezoresponses for 1 and 2 are found to be within the range of 0.24 ─ 3.42 and 0.14 ─ 1.45 pm/V. Polycrystalline discs of both MCCs were electroded with flexible Cu tape, yielding maximum output voltages of 102.6 and 75.7 mV, respectively, upon low level mechanical stimulation.