Unusual Two–step Switchable Dielectric Behaviors and FerroelasticPhase Transition in a Simple 18‐Crown‐6 Clathrate

Abstract

The molecular multi‐sequential phase transition accompanying with perfect switchable dielectric behaviors and ferroelastic properties are seldom reported. Here we investigated unusual two‐step reversible structural phase transitions which consist of a ferroelastic phase transition and a special structural phase transition without symmetry breaking in a simple clathrate of 18‐Crown‐6 phosphofluoric acid monohydrate, (1). The further molecular dynamic by variable temperature X‐ray Single crystal diffraction and Powder X‐ray diffractions were disclosed that it was driven by two distinct rotation motions namely compass‐like rotation and windlass‐like rotation. Two pairs of distinct reversible step‐like dielectric anomalies with electrical tristabilities among high, middle and low dielectric states at 278/281 K and 292/296 K in heating/cooling runs suggest that it can be a potential switchable dielectric molecular material within a narrow temperaturespan (15 K). The DSC curves show analogous heat anomalies at the same temperatures and further confirm the reversible phase transition behaviors.

High-temperature ferroelastic phase transition in a perovskite-like complex: [Et4N]2[PbBr3]2

“…The distances of N and C atoms vary from 1.479(8) to 1.541(8)Å, the angles of C-N-C vary from 106.20 (5) to 112.20 (5) . Whereas in the HTP, with each Pb1 atom occupying the 3m symmetry site, the Pb-Br bond distance changes to 3.030(1)Å and the Br-Pb-Br bond angles are in the range from 81.59 (10) to 98.41 (10) . The C-N bond lengths vary from 1.480(2) to 1.500(2)Å and the C-N-C bond angles vary from 108.40 (18) to 110.60 (18) (Table S3 †).…”

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

“…Amongc ompound 3 exists ap hase transition around 135 K, both the higha nd low temperature structuresh ave the same centro-symmetrical cubic group Fd-3. [38] Another compound 2 displays a para-ferroelasitc phase transition from Pnma to P2 1 /c at 292 K. [31] To tally different from the linear infinite structureo fc ompound 4,c ompound 1 has ad iscrete structure. Here we depicted the crystal structures of 1-LTP and 1-HTP at length.…”

“…Since compounds 2a nd 3h ave been published by our previous work, [31,38] here we just focused on the synthesis and characterizations of compounds 1 and 4.C ompound 1 was prepared as Scheme 1. 18-Crown-6 (0.2643 g,1 mmol) was added in ac lean 50 mL beaker,t hen hexafluorophosphoric acid solution (0.1459 g, 1mmol) was dropped into the beaker.T he mixture was stirred vigorously for an hour then filtered.…”

“…[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. [12,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Therefore, our strategy is to keep the body structure of this non-ferroelectric phase transition molecular system with tiny local modifications, such molecular tailoring operation may retain the "driving force" of the body structure but reducei ts symmetry to introduce ad ipole moment into such molecular system, and then potentially construct novel ferroelectrics from such non-ferroelectricm olecular compound. In this way,X iong.…”

High‐Temperature Reversible Phase‐Transition Behavior, Switchable Dielectric and Second Harmonic Generation Response of Two Homochiral Crown Ether Clathrates

“…As molecular reversible phase transition materials were continuously discovered, higherr equirementsa re focusedo nt he exploration of high molecular phase transition temperature and multiple functional molecular materials (such as SHG responses, chirality) because of their excellentp erformance and practicality.I nspiringly,anew class of compounds, namely the crown ether clathrates has attracted great attentioni nr ecent years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] These clathrates tend to form a" stator-rotor" configuration with protonated organic amine cations and deprotonated inorganic acid anions. [17][18][19][20][21] When the temperature changes,t he protonated organic aminec ation often acts as a rotor and undergoes slightt orsion or order-disorder change, sometimes the crown ether rings may also undergo order-disorder rotation, therebyi nducing the reversible phase transition.…”