H/F substitution for advanced molecular ferroelectrics

Ferroelasticity, thermochromism, semi-conductivity, and ferromagnetism in a new layered perovskite: (4-fluorophenethylaminium)2[CuCl4]

“…[21][22][23][26][27][28] In particular, fluorine substitution on phenyl rings has been proved as an effective design strategy to regulate the properties of hybrid materials. [29][30][31][32] Fluorine is the most electronegative element and has a similar van der Waal's radius to that of the hydrogen atom, thus the fluorine substitution usually causes slight structural distortion but significantly tunes or improves the stability and physical properties of materials, 32 e.g., endowing (perfluorobenzylammonium) 2 [PbBr 4 ] and (2-fluorobenzylammonium) 2 [PbCl 4 ] with increased ferroelectric transition temperatures, 31,32 while bringing about a symmetry-reduced room-temperature phase for (FPEA) 2 [MCl 4 ] (M = Cd, Mn, FPEA + = 4-fluorophenethylaminium). 30 On the other hand, many transition metal ions are compatible in layered perovskites, bringing about fascinating properties such as magnetism, fluorescence, and thermochromism.…”

Ferroelastic phase transition with large spontaneous strain caused by freezing the conformational dynamics of ammonium

“…Recently, phase transitions in hybrid organic–inorganic complexes have attracted growing interest since their symmetry breaking can be designed at the molecular level. 6 The order and disorder transformations of the ionic molecule components can trigger changes in the symmetry, causing structural phase transitions. 7 A typical example in designing ferroelectric materials is the “quasi-spherical theory” proposed by Xiong et al , in which freezing the rotation of the quasi-spherical organic cations affords ferroelectric or ferroelastic phase transitions.…”

High temperature hybrid perovskite multifunctional switching materials constructed through precise molecular design

“…Among OIHPs, molecular phase transition materials with the reversibility of intrinsic responses upon external stimuli (such as temperature, electric field and pressure) have attracted much attention due to their wide application in information processing, sensors, actuators, nonlinear optical components, energy conversion and mechanical switches. [12][13][14][15] Nonetheless, nowadays, the reported OIHP molecular switching materials show low phase transition temperatures (T p ) and only single-switching (dielectric switching) or double-switching (dielectric switching and ferroelastic switching or dielectric switching and nonlinear switching) characteristics. [16][17][18][19] In particular, high T p OIHP materials with three kinds of switching characteristics are highly desirable and there are great challenges in the design of these multifunctional materials because the dynamic motion of internal components in a crystal lattice is hard to control.…”

“…However, the different electronegativity and polarization of H and F can cause significant differences in the physical and chemical properties of the system. 15 For example, Fu and co-workers have reported [NH 3 CH 2 CH 2 F] 3 BiCl 6 through replacement of the H by F in [NH 3 CH 2 CH 3 ] 3 BiCl 6 , which makes the T p increase from 229 to 361.5 K and exhibits dielectric and nonlinear dual-switching properties. 16 Another compound reported by Fu and Ye is [DMIFE][Cd(SCN) 3 ] with a T p of 295.9 K, which is obtained by H/F substitution from the prototype [DMIE][Cd(SCN) 3 ] ([DMIE] + is the dimethyl-isopropyl-ethyl-ammonium cation) with a T p of 248.6 K. 17 The common feature of the compounds mentioned above is that they have relatively low T p values or their functions need to be developed, which hinders their practical application in complex environments.…”