Competitive Halogen Bond in the Molecular Ferroelectric with Large Piezoelectric Response

Molecular piezoelectrics are attracting tremendous interest because of their easy processing, light weight, low acoustical impedance, and mechanical flexibility. However, reports of molecular piezoelectrics with a piezoelectric coefficient <i>d</i>₃₃ comparable to piezoceramics such as barium titanate (BTO, 90–190 pC/N) have been scarce. Here, we present a uniaxial molecular ferroelectric, trimethylchloromethylammonium tribromocadmium­(II) (TMCM-CdBr₃), in which the halogen bonding might be a possible critical point for the stabilization of one-dimensional (1D) {CdBr₃}⁻ chain and further reservation of its ferroelectricity in such organic–inorganic hybrid crystalline systems. It has a large <i>d</i>₃₃ of 139 pC/N, 1 order of magnitude higher than those of most classically uniaxial ferroelectrics such as LiNbO₃ (6–16 pC/N) and Rochelle salt (∼7 pC/N), and comparable with those of multiaxial ferroelectrics such as BTO and trimethylbromomethylammonium tribromomanganese­(II) (112 pC/N). Moreover, the simple single-crystal growth and easy-to-find polar axis enable it to hold a great potential for applying in the single-crystal form. In light of the strong, specific, and directional halogen-bonding interactions, this work provides possibilities to explore new classes of molecular piezoelectrics and contribute to further developments

Competitive Halogen Bond in the Molecular Ferroelectric with Large Piezoelectric Response

Molecular piezoelectrics are attracting tremendous interest because of their easy processing, light weight, low acoustical impedance, and mechanical flexibility. However, reports of molecular piezoelectrics with a piezoelectric coefficient <i>d</i>₃₃ comparable to piezoceramics such as barium titanate (BTO, 90–190 pC/N) have been scarce. Here, we present a uniaxial molecular ferroelectric, trimethylchloromethylammonium tribromocadmium­(II) (TMCM-CdBr₃), in which the halogen bonding might be a possible critical point for the stabilization of one-dimensional (1D) {CdBr₃}⁻ chain and further reservation of its ferroelectricity in such organic–inorganic hybrid crystalline systems. It has a large <i>d</i>₃₃ of 139 pC/N, 1 order of magnitude higher than those of most classically uniaxial ferroelectrics such as LiNbO₃ (6–16 pC/N) and Rochelle salt (∼7 pC/N), and comparable with those of multiaxial ferroelectrics such as BTO and trimethylbromomethylammonium tribromomanganese­(II) (112 pC/N). Moreover, the simple single-crystal growth and easy-to-find polar axis enable it to hold a great potential for applying in the single-crystal form. In light of the strong, specific, and directional halogen-bonding interactions, this work provides possibilities to explore new classes of molecular piezoelectrics and contribute to further developments

Competitive Halogen Bond in the Molecular Ferroelectric with Large Piezoelectric Response

Molecular piezoelectrics are attracting tremendous interest because of their easy processing, light weight, low acoustical impedance, and mechanical flexibility. However, reports of molecular piezoelectrics with a piezoelectric coefficient <i>d</i>₃₃ comparable to piezoceramics such as barium titanate (BTO, 90–190 pC/N) have been scarce. Here, we present a uniaxial molecular ferroelectric, trimethylchloromethylammonium tribromocadmium­(II) (TMCM-CdBr₃), in which the halogen bonding might be a possible critical point for the stabilization of one-dimensional (1D) {CdBr₃}⁻ chain and further reservation of its ferroelectricity in such organic–inorganic hybrid crystalline systems. It has a large <i>d</i>₃₃ of 139 pC/N, 1 order of magnitude higher than those of most classically uniaxial ferroelectrics such as LiNbO₃ (6–16 pC/N) and Rochelle salt (∼7 pC/N), and comparable with those of multiaxial ferroelectrics such as BTO and trimethylbromomethylammonium tribromomanganese­(II) (112 pC/N). Moreover, the simple single-crystal growth and easy-to-find polar axis enable it to hold a great potential for applying in the single-crystal form. In light of the strong, specific, and directional halogen-bonding interactions, this work provides possibilities to explore new classes of molecular piezoelectrics and contribute to further developments

Competitive Halogen Bond in the Molecular Ferroelectric with Large Piezoelectric Response

Molecular piezoelectrics are attracting tremendous interest because of their easy processing, light weight, low acoustical impedance, and mechanical flexibility. However, reports of molecular piezoelectrics with a piezoelectric coefficient <i>d</i>₃₃ comparable to piezoceramics such as barium titanate (BTO, 90–190 pC/N) have been scarce. Here, we present a uniaxial molecular ferroelectric, trimethylchloromethylammonium tribromocadmium­(II) (TMCM-CdBr₃), in which the halogen bonding might be a possible critical point for the stabilization of one-dimensional (1D) {CdBr₃}⁻ chain and further reservation of its ferroelectricity in such organic–inorganic hybrid crystalline systems. It has a large <i>d</i>₃₃ of 139 pC/N, 1 order of magnitude higher than those of most classically uniaxial ferroelectrics such as LiNbO₃ (6–16 pC/N) and Rochelle salt (∼7 pC/N), and comparable with those of multiaxial ferroelectrics such as BTO and trimethylbromomethylammonium tribromomanganese­(II) (112 pC/N). Moreover, the simple single-crystal growth and easy-to-find polar axis enable it to hold a great potential for applying in the single-crystal form. In light of the strong, specific, and directional halogen-bonding interactions, this work provides possibilities to explore new classes of molecular piezoelectrics and contribute to further developments

Large Piezoelectric Effect in a Lead-Free Molecular Ferroelectric Thin Film

Piezoelectric materials have been widely used in various applications, such as high-voltage sources, actuators, sensors, motors, frequency standard, vibration reducer, and so on. In the past decades, lead zirconate titanate (PZT) binary ferroelectric ceramics have dominated the commercial piezoelectric market due to their excellent properties near the morphotropic phase boundary (MPB), although they contain more than 60% toxic lead element. Here, we report a lead-free and one-composition molecular ferroelectric trimethylbromomethylammonium tribromomanganese­(II) (TMBM-MnBr₃) with a large piezoelectric coefficient <i>d</i>₃₃ of 112 pC/N along polar axis, comparable with those of typically one-composition piezoceramics such as BaTiO₃ along polar axis [001] (∼90 pC/N) and much greater than those of most known molecular ferroelectrics (almost below 40 pC/N). More significantly, the effective local piezoelectric coefficient of TMBM-MnBr₃ films is comparable to that of its bulk crystals. In terms of ferroelectric performance, it is the low coercive voltages, combined with the multiaxial characteristic, that ensure the feasibility of piezo film applications. Based on these, along with the common superiorities of molecular ferroelectrics like light weight, flexibility, low acoustical impedance, easy and environmentally friendly processing, it will open a new avenue for the exploration of next-generation piezoelectric devices in industrial and medical applications

Chiral Molecular Ferroelectrics with Polarized Optical Effect and Electroresistive Switching

Multifunctional properties of chiral molecules arise from the coexistence of mirror-symmetry-induced stereoisomers and optical rotation characteristics in one material. One of these complex phenomena in these molecules is chiral ferroelectricity, providing the coupling between polarized light and the spatial asymmetry induced dipole moment. Herein we describe the chiral polarization and electroresistance in molecular ferroelectric (<i>R</i>)-(−)-3-hydroxyquinuclidinium chloride thin films with a Curie temperature of 340 K. The high transmittance of chiral ferroelectrics is coupled with polarized light for a linear electro-optic effect, which exhibits angle-dependent optical behaviors. The polarization-controlled conductance imposes a large on/off ratio (∼26.6) of electroresistive switching in molecular ferroelectrics with superior antifatigue endurance

De Novo Discovery of [Hdabco]BF₄ Molecular Ferroelectric Thin Film for Nonvolatile Low-Voltage Memories

To date, the field of ferroelectric random access memories (FeRAMs) is mainly dominated by inorganic ferroelectric thin films like Pb­(Zr,Ti)­O₃, which suffer from the issues of environmental harmfulness, high processing temperatures, and high fabrication costs. In these respects, molecular ferroelectric thin films are particularly advantageous and thus become promising alternatives to the conventional inorganic ones. For the prospect of FeRAMs applications, they should fulfill the requirements of effective polarization switching and low-voltage, high-speed operation. Despite recent advancements, molecular ferroelectric thin films with such high performance still remain a huge blank. Herein we present the first example of a large-area continuous biaxial molecular ferroelectric thin film that gets very close to the goal of application in FeRAMs: [Hdabco]­BF₄ (dabco = diazabicyclo[2.2.2]­octane). In addition to excellent film performance, it is the coexistence of a low coercive voltage of ∼12 V and ultrafast polarization switching at a significantly high frequency of 20 kHz that affords [Hdabco]­BF₄ considerable potential for memory devices. Particularly, piezoresponse force microscopy (PFM) clearly demonstrates the four polarization directions and polarization switching at a low voltage down to ∼4.2 V (with an ∼150 nm thick film). This innovative work on high-performance molecular ferroelectric thin films, which can be compatible with wearable devices, will inject new vitality to the low-power information field

Unprecedented Ferroelectric–Antiferroelectric–Paraelectric Phase Transitions Discovered in an Organic–Inorganic Hybrid Perovskite

As a promising candidate for energy storage capacitors, antiferroelectric (AFE) materials have attracted great concern due to their congenital advantages of large energy storage ability from double polarization versus electric field (<i>P</i>–<i>E</i>) hysteresis characteristics in contrast to ferroelectrics and linear dielectrics. However, antiferroelectricity has only been discovered in inorganic oxides and some hydrogen-bonded molecular systems. In view of the structural diversity and unique physical properties of organic–inorganic hybrid system, it remains a great opportunity to introduce antiferroelectricity into organic–inorganic hybrid perovskites. Here, we report that polarizable antiparallel dipole arrays can be realized in an organic–inorganic hybrid perovskite, (3-pyrrolinium)­CdBr₃, which not only exhibits an excellent ferroelectric property (with a high spontaneous polarization of 7.0 μC/cm²), but also presents a striking AFE characteristic revealed by clear double <i>P</i>–<i>E</i> hysteresis loops. To the best of our knowledge, it is the first time that such successive ferroelectric–antiferroelectric–paraelectric phase transitions have been discovered in organic–inorganic perovskites. Besides, a giant dielectric constant of 1600 even at high frequency of 1000 kHz and a bulk electrocaloric effect with entropy change of 1.18 J K^–1 kg^–1 under 7.41 kV/cm are also observed during the phase transition. Apparently, the combined striking AFE characteristic and giant dielectric constant make (3-pyrrolinium)­CdBr₃ a promising candidate for next generation high-energy-storage capacitors

Unprecedented Ferroelectric–Antiferroelectric–Paraelectric Phase Transitions Discovered in an Organic–Inorganic Hybrid Perovskite

As a promising candidate for energy storage capacitors, antiferroelectric (AFE) materials have attracted great concern due to their congenital advantages of large energy storage ability from double polarization versus electric field (<i>P</i>–<i>E</i>) hysteresis characteristics in contrast to ferroelectrics and linear dielectrics. However, antiferroelectricity has only been discovered in inorganic oxides and some hydrogen-bonded molecular systems. In view of the structural diversity and unique physical properties of organic–inorganic hybrid system, it remains a great opportunity to introduce antiferroelectricity into organic–inorganic hybrid perovskites. Here, we report that polarizable antiparallel dipole arrays can be realized in an organic–inorganic hybrid perovskite, (3-pyrrolinium)­CdBr₃, which not only exhibits an excellent ferroelectric property (with a high spontaneous polarization of 7.0 μC/cm²), but also presents a striking AFE characteristic revealed by clear double <i>P</i>–<i>E</i> hysteresis loops. To the best of our knowledge, it is the first time that such successive ferroelectric–antiferroelectric–paraelectric phase transitions have been discovered in organic–inorganic perovskites. Besides, a giant dielectric constant of 1600 even at high frequency of 1000 kHz and a bulk electrocaloric effect with entropy change of 1.18 J K^–1 kg^–1 under 7.41 kV/cm are also observed during the phase transition. Apparently, the combined striking AFE characteristic and giant dielectric constant make (3-pyrrolinium)­CdBr₃ a promising candidate for next generation high-energy-storage capacitors

Unprecedented Ferroelectric–Antiferroelectric–Paraelectric Phase Transitions Discovered in an Organic–Inorganic Hybrid Perovskite

As a promising candidate for energy storage capacitors, antiferroelectric (AFE) materials have attracted great concern due to their congenital advantages of large energy storage ability from double polarization versus electric field (<i>P</i>–<i>E</i>) hysteresis characteristics in contrast to ferroelectrics and linear dielectrics. However, antiferroelectricity has only been discovered in inorganic oxides and some hydrogen-bonded molecular systems. In view of the structural diversity and unique physical properties of organic–inorganic hybrid system, it remains a great opportunity to introduce antiferroelectricity into organic–inorganic hybrid perovskites. Here, we report that polarizable antiparallel dipole arrays can be realized in an organic–inorganic hybrid perovskite, (3-pyrrolinium)­CdBr₃, which not only exhibits an excellent ferroelectric property (with a high spontaneous polarization of 7.0 μC/cm²), but also presents a striking AFE characteristic revealed by clear double <i>P</i>–<i>E</i> hysteresis loops. To the best of our knowledge, it is the first time that such successive ferroelectric–antiferroelectric–paraelectric phase transitions have been discovered in organic–inorganic perovskites. Besides, a giant dielectric constant of 1600 even at high frequency of 1000 kHz and a bulk electrocaloric effect with entropy change of 1.18 J K^–1 kg^–1 under 7.41 kV/cm are also observed during the phase transition. Apparently, the combined striking AFE characteristic and giant dielectric constant make (3-pyrrolinium)­CdBr₃ a promising candidate for next generation high-energy-storage capacitors