Bistable State of Protons for Low-Voltage Memories

Abstract

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmental-friendly processing, low acoustic impedance, and mechanical flexibility. Their ferroelectric mechanism is mainly ascribed to the order–disorder transition of molecules such as spherical 1,4-diazabicyclo[2.2.2] octane (DABCO) and quinuclidine. Here, we present two molecular ferroelectrics, [HDABCO]­[TFSA] and its deuterated one [DDABCO]­[TFSA] (TFSA = bis­(trifluoro­methylsulfonyl)­ammonium), whose ferroelectricity is triggered by the proton ordering. This is the first time that the protons show a thermally fluctuated bistability with a double-well potential in DABCO-based ferroelectrics. A large deuterium isotope effect (ΔT = ∼53 K) not only proves that they are hydrogen-bonded ferroelectrics but also extends the ferroelectric working temperature range to room temperature. The superfast polarization switching of 100 kHz and ultralow coercive voltage of 1 V (far less than 5 V required for commercially available ferroelectric devices), benefiting from the low energy for proton transfer, allow [DDABCO]­[TFSA] a great potential for memory devices with low-voltage, high-speed operation. This work should inspire further exploration of hydrogen-bonded molecular ferroelectrics for flexible and wearable devices with the low-power information storage.

Record Enhancement of Phase Transition Temperature Realized by H/F Substitution

“…This temperature enhancement (229 K) is the largest among reported enhancements for molecular ferroelectrics, far beyond those enhancements observed using the isotope effect or other techniques. [11,15,[32][33][34][35][36][37][38] Moreover, (4-FABCH)CdCl 3 is also a multiaxial ferroelectric with an Aizu notation of 6 2 m Fmm2. The novel and effective strategy presented in this paper represents a crucial step toward the development of high-T c molecular ferroelectrics and should inspire future development of ferroelectric devices and technologies.…”

“…Notably, the organic cations were in an ordered state at LTP but highly disordered at HTP. The cations of (ABCH)CdCl 3 , which have one less carbon atom than quinuclidine, demonstrated a quasi-spherical [15] ND 4 D 2 PO 4 , [37] KDPO 4 , [35] (DDABCO) 2 (TCNQ) 3 (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane), [11] Phz-D 2 ba (Phz = phenazine and D 2 ba = deuterated bromanilic acid), [34] (R)-and (S)-3-F-(pyrrolidinium)CdCl 3 , [31] Phz-D 2 ca (Phz = phenazine and D 2 ca = deuterated chloranilic acid), [34] (R)-and (S)-3-(fluoropyrrolidinium) MnCl 3 , [30] (ND 2 CH 2 COOD) 3 D 2 SeO 4 , [33] D 2 S (deuterium sulfides), [36] [DDABCO][TFSA] (TFSA = bis(trifluoromethylsulfonyl)ammonium), [38] and PD-DMACoF ([(CD 3 ) 2 ND 2 ]Co(DCOO) 3 ). [32] geometry, similar to (4-FABCH)CdCl 3 .…”

Hydrogen‐Bonded Engineering Enhancing Phase Transition Temperature in Molecular Perovskite Ferroelastic

“…[ 6‐9 ] Among them, the deuteration effect has been as a strategy to alter the H‐bonds, inducing different properties or producing new characteristics. [ 10‐12 ] For example, hydrogen‐bonded ferroelectric potassium dihydrogen phosphate (KH 2 PO 4 , KDP) has a great phase transition temperature increased by the deuteration effect. [ 13 ] This result can be attributed to increased intermolecular forces.…”

H/F substitution for advanced molecular ferroelectrics

“…Much effort has been devoted to improving the T c of molecular ferroelectrics for its vital significance in practical applications above room temperature. In pursuit of high-performance molecular ferroelectrics, the isotope effect can contribute to, but is only limited to, the hydrogen-bonded ferroelectrics for the enhancement of their physical properties [22]. It should be noted that the introduction of a D atom normally does not lead to the change of structural symmetry but largely improves the T c and spontaneous polarization (P s ) [23][24][25].…”