Record Enhancement of Curie Temperature in Host–Guest Inclusion Ferroelectrics

Abstract

Solid-state molecular rotor-type materials such as host–guest inclusion compounds are very desirable for the construction of molecular ferroelectrics. However, they usually have a low Curie temperature (T c) and uniaxial nature, severely hindering their practical applications. Herein, by regulating the anion to control “momentum matching” in the crystal structure, we successfully designed a high-temperature multiaxial host–guest inclusion ferroelectric [(MeO–C6H4–NH3)­(18-crown-6)]­[TFSA] (MeO–C6H4–NH3 = 4-methoxyanilinium, TFSA = bis­(trifluoromethanesulfonyl)­ammonium) with the Aizu notation of mmmFm. Compared to the parent uniaxial ferroelectric [(MeO–C6H4–NH3)­(18-crown-6)]­[BF4] with a T c of 127 K, the introduction of larger TFSA anions brings a lower crystal symmetry at room temperature and a higher energy barrier of molecular motions in phase transition, giving [(MeO–C6H4–NH3)­(18-crown-6)]­[TFSA] multiaxial ferroelectricity and a high T c up to 415 K (above that of BaTiO3). To our knowledge, such a record temperature enhancement of 288 K makes its T c the highest among the reported crown-ether-based ferroelectrics, giving a wide working temperature range for applications in data storage, temperature sensing, actuation, and so on. This work will provide guidance and inspiration for designing high-T c host–guest inclusion ferroelectrics.

Stabilization of Ferroelectric Phase in Highly Oriented Quinuclidinium Perrhenate (HQReO4) Thin Films

“…Plastic molecular crystals exhibiting switchable polarization are a unique class of ferroelectric (FE) materials owing to their environmental friendliness, structural tunability, and mechanical flexibility [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Compared to inorganic FE materials, the low-temperature processibility of plastic crystals makes it an attractive choice for FE applications [ 9 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. The major drawback of molecular ferroelectric crystals are their low spontaneous polarization, low melting temperature, low Curie temperature, and small dielectric constant, which needs to be improved for replacing it with the inorganic FE materials [ 23 ].…”

“…The major drawback of molecular ferroelectric crystals are their low spontaneous polarization, low melting temperature, low Curie temperature, and small dielectric constant, which needs to be improved for replacing it with the inorganic FE materials [ 23 ]. Several molecular FE compounds have been investigated; however, many practical challenges exist—such as controlling crystal orientations and polarization directions, making it difficult to manipulate the FE properties [ 8 , 12 , 13 , 14 , 15 , 18 , 21 , 23 ]. When compared to bulk FE crystals, inorganic FE thin films have a much broader impact and applications in microelectronics [ 24 ].…”

The First High‐Temperature Supramolecular Radical Ferroics

“…[1] Among them, ferroics have av ariety of technological utilizations,a smemories,s ensors,a ctuators,e tc. [2] It should be underlined that numerous crown-ether based hostguest inclusion compounds have been discovered with excellent ferroicity,i ncluding [(C 7 H 10 NO)( [18]crown-6)]-[ReO 4 ]/[ClO 4 ]/[BF 4 ]( C 7 H 10 NO = 4-methoxyanilinium), [1e, 3] Ca(NO 3 ) 2 ( [15]crown-5), [4] [(H 3 O)( [18]crown-6)][GaCl 4 ], [5] [(DIPA)( [18]crown-6)][ClO 4 ]/[BF 4 ]( DIPA = 2,6-diisopropylanilinium), [6] [(Hcha)( [18]crown-6)][ClO 4 ]/[BF 4 ]( Hcha = protonated cyclohexyl ammonium), [7] [(MeO-C 6 H 4 -NH 3 )-( [18]crown-6)][TFSA] (MeO-C 6 H 4 -NH 3 = 4-methoxyanilinium, TFSA = bis(trifluoromethanesulfonyl)ammonium) [8] and (m-FAni + )(dibenzo [18]crown -6)[Ni(dmit) 2 ] À (m-FA-ni + = m-fluoroanilinium, dmit 2À = 2-thioxo-1,3-dithiole-4,5dithiolate). [9] Among them, nearly all the guest ions are organic amine.R ecently,s upramolecular chemistry also extends to the realm of radicals,f or which the weak forces involved in the supramolecular system may control ar adical in an unexpected way.…”

“…Now the question arises: how can we design astable radical compound, and will it also be ah igh-temperature ferroic?I ts hould be highlighted that with the underlying idea of momentum matching theory, [(MeO-C 6 H 4 -NH 3 )( [18]crown-6)][TFSA] realizes the record enhancement of T c in host-guest inclusion ferroelectrics. [8] Momentum matching theory,achemical design approach for organic ferroelectrics,refers that the different components within one system should present areasonable interaction and follow as uitable matching degree. [17] Furthermore,s upramolecular architectures play akey role in the stabilization of masses of fleeting species,especially for radicals.…”

“…Herein, based on the universal chemical design methods, we synthesized two organic high-temperature supramolecular radical ferroics,[ (NH 3 -TEMPO)( [18]crown-6)](ReO 4 )( 1) and [(NH 3 -TEMPO)( [18]crown-6)](ClO 4 )( 2)( Scheme 1), which can retain the ferroelectricity up to 413 Ka nd 450 K, respectively.A sf ar as we are aware,4 50 Ki st he highest temperature at which ferroelectric properties can be maintained among the reported crown-ether-based ferroelectrics, offering awide working temperature range for applications. [8] Them easured spontaneous polarization (P s )o f1 is about 6.2 mCcm À2 ,a mong the largest one in molecular ferroelectrics.I ts hould be noted that 1 and 2 show ar elatively high piezoelectric response of 13 pC N À1 and 17 pC N À1 ,c omparable with that of LiNbO 3 (6-16 pC N À1 ). [20] To our knowledge, 1 and 2 are the first examples of supramolecular radical ferroics,p ossessing excellent piezoelectricity as well as good ferroelectricity.A sa nticipated, this successful chemical design suggests that 1 and 2 would become suitable candidates for future applications owing to the significant extending of their ferroic temperature windows from low-temperature to room-temperature or even high-temperature range.W ea lso investigate the magnetic properties of 1 and 2,demonstrating the existence of an unpaired electron as well as the paramagnetism.…”