Ultrafast Polarization Switching in a Biaxial Molecular Ferroelectric Thin Film: [Hdabco]ClO₄

Abstract

Molecular ferroelectrics are attracting much attention as valuable complements to conventional ceramic ferroelectrics owing to their solution processability and nontoxicity. Encouragingly, the recent discovery of a multiaxial molecular ferroelectric, tetraethylammonium perchlorate, is expected to be able to solve the problem that in the technologically relevant thin-film form uniaxial molecular ferroelectrics have been found to perform considerably more poorly than in bulk. However, it can show good polarization-electric field (P-E) hysteresis loops only at very low frequency, severely hampering practical applications such as ferroelectric random access memory. Here, we present a biaxial molecular ferroelectric thin film of [Hdabco]ClO (dabco = 1,4-diazabicyclo[2.2.2]octane) (1), where a perfect ferroelectric hysteresis loop can be observed even at 10 kHz. It is the first example of a molecular ferroelectric thin film whose polarization can be switched at such a high frequency. Moreover, using piezoresponse force microscopy, we clearly observed the coexistence of 180° and non-180° ferroelectric domains and provided direct experimental proof that 180° ferroelectric switching and non-180° ferroelastic switching are both realized; that is, a flexible alteration of the polarization axis direction can occur in the thin film by applying an electric field. These results open a new avenue for applications of molecular ferroelectrics and will inspire further exploration of high-performance multiaxial molecular ferroelectric thin films.

Polarization‐Driven Self‐Powered Photodetection in a Single‐Phase Biaxial Hybrid Perovskite Ferroelectric

“…Related to FEP,t he most evident change is that both the "perovskitizer" MA + and the "spacer" EA + cations transform into highly disordered states (Figure 2b). Meanwhile,t he distorted inorganic [PbBr 6 ] 4À octahedra assume highly symmetric configurations.T hese transformations make the positive and negative charge centers overlap,f orming ap araelectric state at high temperature.Notably,accompanying the phase transition from PEP to FEP,s ymmetry breaking occurs in 1 with spontaneous polarization emerging along the [110] direction ( Figure S4), resembling that of molecular ferroelectric [Hdabco]ClO 4 (dabco = 1,4-diazabicyclo[2.2.2]octane) [13] and hybrid perovskite ferroelectric EA 4 Pb 3 Br 10 . [14] Meanwhile,t he symmetry …”

A Molecular Polycrystalline Ferroelectric with Record‐High Phase Transition Temperature

“…Molecular ferroelectrics consisting of multiatom groups often have relatively low symmetry and uniaxial nature with only two opposite polarization directions. However, most ferroelectric materials are utilized in the polycrystalline forms like ceramic or thin film, so they would better be multiaxial to allow the polarizations of individual grains to be oriented along the applied electric field as much as possible and hence to achieve a larger polarization upon poling . This is because the efficiency of polarization switching in the polycrystalline state relies on the available ferroelectric axes, the maximum remanent polarization ( P r ) max could reach 0.25 P s and 0.9 P s (spontaneous polarization of the single‐crystal state) in the uniaxial and multiaxial cases, respectively .…”

Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

“…Ferroelectric molecular crystals are advantageous because of their low weights,l ow costs,e nvironmental friendliness, chemical convenience,a nd low toxicities. [1][2][3][4][5][6][7][8][9][10][11] Because molecules are intrinsically packed closely in their crystals,e lectrically reversing the polarizations of molecular species in order to engineer molecular ferroelectrics requires aunique regime. Thet hermally induced orientational motion of polar molecules has been developed as an efficient method for the electrical switching of polarization.…”

“…Thet hermally induced orientational motion of polar molecules has been developed as an efficient method for the electrical switching of polarization. Ther equired active thermal motion has been achieved by supramolecular cations, [3] plastic crystals, [9,10] and organic-inorganic perov-skites. [4] Recently,X iong and co-workers developed ferroelectric metal-free molecular perovskites.…”

“…[11] Significant attention has been paid to derivatives of cationic heterocyclic organic molecules with spherical shapes,f or example 1,4diazabicyclo[2.2.2]octane (dabco), as possible polar rotators. [9,10] We were inspired by hexamethylenetetramine (hmta) as ap ossible molecular-ferroelectric candidate;this molecule is an on-centrosymmetric but highly symmetrical analogue of dabco ( Figure 1), possessing tetrahedral (T d )symmetry about four Na toms.A sopposed to traditional ferroelectric compounds composed of "spherical" inorganic ions,m olecular ferroelectrics uniquely control their lattice symmetries through molecular shape.T he features of hmta are attractive for ferroelectrics;hence,the development of alarge family of materials based on hmta is expected. However,b ecause of their instabilities in acidic media, [12] few isolated examples have been reported.…”