Fluorine Substitution Induced High T_c of Enantiomeric Perovskite Ferroelectrics: (R)- and (S)-3-(Fluoropyrrolidinium)MnCl₃

Abstract

The past decade has witnessed much progress in designing molecular ferroelectrics, whose intrinsic mechanical flexibility, structural tunability, and easy processability are desirable for next-generation flexible and wearable electronic devices. However, an obstacle in expanding their promising applications in nonvolatile memory elements, capacitors, and sensors is effectively modulating the Curie temperature (T c ).Here, taking advantage of fluorine substitution on the reported molecular ferroelectric, (pyrrolidinium)MnCl 3 , we present enantiomeric perovskite ferroelectrics, namely, (R)and (S)-3-(fluoropyrrolidinium)MnCl 3 . The close van der Waal's radii and the similar steric parameters between H and F atoms ensure the minimum disruption of the crystal structure, while their different electronegativity and polarizability can trigger significant changes in the physical and chemical properties. As expected, the T c gets successfully increased from 295 K in (pyrrolidinium)MnCl 3 to 333 K in these two homochiral compounds. Such a dramatic enhancement of 38 K signifies an important step toward designing high-T c molecular ferroelectrics. In the light of the conceptually new idea of fluorine substitution, one could look forward to a continuous succession of new molecular ferroelectric materials and technology developments.

A Nickel(II) Nitrite Based Molecular Perovskite Ferroelectric

“…Abstract: The X-site ion in organic-inorganic hybrid ABX 3 perovskites (OHPs) varies from halide ion to bridging linkers like HCOO À ,N 3 À ,NO 2 À ,and CN À .However,nonitrite-based OHP ferroelectrics have been reported so far.N ow,b ased on non-ferroelectric [(CH 3 ) 4 N][Ni(NO 2 ) 3 ], through the combined methodologies of quasi-spherical shape,h ydrogen bonding functionality,a nd H/F substitution, we have successfully synthesized an OHP ferroelectric, [FMeTP][Ni(NO 2 ) 3 ] (FMeTP = N-fluoromethyl tropine). As an unprecedented nitrite-based OHP ferroelectric,t he well-designed [FMeTP]-[Ni(NO 2 ) 3 ]u ndergoes the ferroelectric phase transition at 400 Kwith an Aizu notation of 6/mmmFm, showing multiaxial ferroelectric characteristics.T his work is ag reat step towards not only enriching the molecular ferroelectric families but also accelerating the potential practical applications.…”

“…[3b, 4] Remarkably,b y extending the X-site from monatomic anions to bridging linkers like HCOO À , [5] N 3 À , [6] NO 2 À , [7] and CN À , [8] aw ide range of larger and longer organic cations can be accommodated for enriching the OHP families and inducing abundant properties such as ferromagnetism and antiferromagnetism. Fort he classical pseudohalide NO 2 À ,o nly two kinds of inorganic ferroelectrics have been reported, NaNO 2 and MCd(NO 2 ) 3 (M = NH 4 ,K,Rb, Cs,Tl), [9] whereas there are no nitrite-based ferroelectrics in the OHPs.I nt his way,t he earlier work of non-ferroelectric [(CH 3 ) 4 N][Ni(NO 2 ) 3 ], adopting at rigonal centrosymmetric space group P3 m1a t room temperature and undergoing two reversible isostructural phase transitions at above 400 K, renewed our interest. [10] Then the key question arises:c ould this very rare and special OHP system be endowed with ferroelectricity under elaborate design?…”

Designing and Constructing a High‐Temperature Molecular Ferroelectric by Anion and Cation Replacement in a Simple Crown Ether Clathrate

“…The ferroelectric hysteresis loop is ad irect proof for af erroelectric, [1,9,25,51] so we determinedt he single crystal's ferroelectric property of 1 based on the polarization dependence on voltage under different frequencies.A fter the arduouse xploration, we obtained the perfect hysteresis loopsr oughlya long the c-axis direction of the single crystal under 450 Ve lectric filed with frequencies of 16.5, 20 and 50 Hz (Figure 8). The results show that the maximum spontaneousp olarizationi s about 2.18 uC cm À2 (blue line) under 50 Hz, the magnitude is slightly larger than that of most reported molecular ferroelec-trics and very closed to the first classic ferroelectric Rochelle salt (about 2.54 uC cm À2 ).…”

“…Ferroelectric have been found wide application in modern functional materials including random-access memory (RAM), capacitance, sensor,e lectro-optical (photoelectricity and piezoelectricity) and infrared detector etc. [1][2][3][4][5][6] Especially molecular ferroelectric materials have become an ew research focus due to their light weight, flexible, environment-friendly and easily synthesis comparet ot raditional inorganic ferroelectrics. [1,[7][8][9][10][11][12][13] Although ag reat progress have been made in the field of molecular ferroelectrics, the current research of molecular ferroelectrics still facealot of challenges.…”

“…[14][15][16][17][18][19][20][21][22][23][24][25][26] How to precisely design and construct new family molecular ferroelectrics through the regulation of an existing molecule system is ag reat challenge. [1,7,[27][28][29] As is known, to be a ferroelectric it must satisfy some basic conditions, i) undergoes as olid reversible phase transition, ii)the ferroelectric should crystallize in the ten polar point groups1 ,m,2 ,mm2, 3, 3m, 4, 4mm, 6, 6mm, iii)exists as pontaneousp olarization which can be changed by the electric field. [30] In general, al ot of molecular compounds usually undergo reversible phase transitions;h owever,t hey can't be ferroelectrics because they have high structural symmetry and cannot produce the polarization.…”