Switchable Dielectric Material Research Articles

Hydrogen-bonded liquid crystal complexes: A comprehensive study of structure, behaviour and potential applications

Intermolecular hydrogen bond (HB) interaction becomes an intensively studied topic in supramolecular chemistry and soft matter science. Herein, a new series of hydrogen-bonded liquid crystals (HBLCs) composed of 3-flurobenzoic acid derivatives (nOBAF) and 1,4-diazabicyclo [2.2.2] octane (DABCO) has been prepared and characterized by Fourier-transform infrared spectroscopy. The thermal behavior was determined by differential scanning calorimetry and observed by polarized optical microscopy. All complexes were found to exhibit smectic G (SmG) and smectic B (SmB) phases over a wide temperature range. Furthermore, it was found that the thermal stability of these mesophases increases with increasing the alkoxy chain length. The complex dielectric permittivity was reported as a function of frequency in the range 1 Hz–10 MHz. Lower frequency process attributed to the collective fluctuations of azimuthal angle and higher frequencies, associated to the soft mode were observed in SmB. In the SmG, additional to the soft mode (106 Hz) a higher frequency mode (105 Hz) was detected for the first time. The experimental results obtained for these complexes were correlated with density functional theory (DFT) calculations. Furthermore, these results suggest that nOBAF/DABCO has the potential to be switchable dielectric materials.

Effect of Dimensionality on Photoluminescence and Dielectric Properties of Imidazolium Lead Bromides.

Hybrid organic–inorganic lead halide perovskites have emerged as promising materials for various applications, including solar cells, light-emitting devices, dielectrics, and optical switches. In this work, we report the synthesis, crystal structures, and linear and nonlinear optical as well as dielectric properties of three imidazolium lead bromides, IMPbBr3, IM2PbBr4, and IM3PbBr5 (IM+ = imidazolium). We show that these compounds exhibit three distinct structure types. IMPbBr3 crystallizes in the 4H-hexagonal perovskite structure with face- and corner-shared PbBr6 octahedra (space group P63/mmc at 295 K), IM2PbBr4 adopts a one-dimensional (1D) double-chain structure with edge-shared octahedra (space group P1̅ at 295 K), while IM3PbBr5 crystallizes in the 1D single-chain structure with corner-shared PbBr6 octahedra (space group P1̅ at 295 K). All compounds exhibit two structural phase transitions, and the lowest temperature phases of IMPbBr3 and IM3PbBr5 are noncentrosymmetric (space groups Pna21 at 190 K and P1 at 100 K, respectively), as confirmed by measurements of second-harmonic generation (SHG) activity. X-ray diffraction and thermal and Raman studies demonstrate that the phase transitions feature an order–disorder mechanism. The only exception is the isostructural P1̅ to P1̅ phase transition at 141 K in IM2PbBr4, which is of a displacive type. Dielectric studies reveal that IMPbBr3 is a switchable dielectric material, whereas IM3PbBr5 is an improper ferroelectric. All compounds exhibit broadband, highly shifted Stokes emissions. Features of these emissions, i.e., band gap and excitonic absorption, are discussed in relation to the different structures of each composition.

2D lead-free organic–inorganic hybrid exhibiting dielectric and structural phase transition at higher temperatures

A novel switchable molecular dielectric material [3-3-difluorocyclobutylammonium]2CdCl4 was synthesized. It shows a reversible phase transition at 353.95 K and rapid switching and reversibility between high and low dielectric states for several cycles.

Significance of considering pellet molding pressure and dielectric experimental conditions in the [dielectric constant—temperature] response of switchable dielectric molecular materials: illustration on dabcoHBF4 polycrystals

In this study, we investigate the temperature-dependent dielectric response of dabcoHBF4 molecular switchable dielectric materials. This compound made of polycrystals has been shaped into pellets under different controlled applied pressures [0.2–1 GPa]. The dielectric analysis carried out on these samples showed that the mechanical stresses induced by this shaping pressure had a significant effect on the value of the dielectric constant in both the ferroelectric and the paraelectric phase. However, the impact of this pressure remains secondary in the AC electrical conductivity, determined for the first time in these compounds. Thus, conductivity values around 2 × 10–7 S/cm in the ferroelectric phase and 2 × 10–6 S/cm in the paraelectric phase were found. The behavior of these compounds over wide frequency ranges [1–1 MHz] and temperature ramps [0.5–10 K/min] revealed that the frequency had no effect on the transition temperature at the difference of temperature rate as expected in most ferroelectric materials. When decreasing the frequency, the dielectric constant gains in value and can reach values higher than 50 in the ferroelectric phase and 1000 in the paraelectric phase with a frequency solicitation at 10 Hz. At lower frequencies, the Curie–Weiss law is lost in the paraelectric regime and an enhanced rise of the dielectric constant with increasing temperature probably reflects an interfacial polarization mechanism. Finally, this dielectric analysis in frequency, temperature (323–403 K) and along temperature ramps allowed to extract analytical laws of behavior associating some of these parameters. For example, one of these equations will be useful in the choice of the temperature ramp to be applied to optimize the switching time between a ferroelectric and a paraelectric state according to a condition on the value of the desired dielectric constant at the low and high states in the implementation of memories.

Tunable Dielectric Switching of (Quinuclidinium)[MnCl4] Hybrid Compounds

Inorganic–organic hybrid QMnCl (Q = quinuclidinium) crystals were synthesized and characterized. The X-ray and variable-temperature IR/Raman analysis demonstrate that the crystals undergo a reversible structural phase transition, which originates from an order–disorder process and is related to the dynamics of the organic Q cation. Dielectric function measurements disclose a switchability between low (“OFF”) and high (“ON”) dielectric states centered at around 285 K. Owing to a remarkable temperature-dependent dielectric function, this type of molecular compound can represent an interesting tunable and switchable dielectric material for a diverse range of applications.

High-Temperature Switchable Dielectric of an Organic–Inorganic Hybrid Metal Halide with Four-fold Cross-Linking Inorganic Anion Spiral Chains

The understanding of structure–property relationship and exploration of novel physical properties are current research topics of molecular switchable dielectric materials. In this paper, an organic...

Three-Dimensional Metal-Free Molecular Perovskite with a Thermally Induced Switchable Dielectric Response.

Temperature-responsive materials with switching physical properties have been widely researched. Among them, the switchable dielectric perovskite materials show potential applications in the electrical and electronic industries and even the intelligence industries. However, perovskite oxides and hybrid organic-inorganic perovskites, as the most representative switchable dielectric materials, are limited by bad biocompatibility. Herein, we report temperature-dielectric-responsive metal-free perovskite (H2dabco)(NH4)[BF4]3 constructed by the strategy of substituting the B site in the general formula ABX3 (doubly protonated 1,4-diazabicyclo[2.2.2]octane = H2dabco). Meanwhile, structurally similar hybrid material (H2dabco)Rb[BF4]3 was designed as a control. They exhibit similar phase-transition characteristics and dielectric response behaviors around 333 K. More interestingly, the ordered-disordered transformation of their organic "spherical" cations (H2dabco) was deemed to produce their phase transitions and dielectric response switching. Given its ability to generate a dielectric response, (H2dabco)(NH4)[BF4]3 will show the potential application of metal-free perovskite in a future thermal sensing device.

A novel ferroelectric based on quinuclidine derivatives

The compound [(CH3)2CH-C3H17N][CoBr4] (1) based on quinuclidine derivatives was achieved by the solution synthetic method and characterized by elemental analysis, infrared spectroscopy, single-crystal X-ray structural analysis and dielectric measurement, respectively. Variable-temperature single-crystal X-ray diffraction suggested that the compound underwent the phase transition from the space group C2/c to Cc. The polarization curve was measured using the Sawyer-Tower circuit. The structural phase transitions of 1 was ascribed to the distortion of a [(CH3)2CH-C3H17N]2+ cation from this inorganic–organic hybrid material [(CH3)2CH-C3H17N][CoBr4]. The strong change in dielectric anomalies makes compound 1 a suitable candidate for promising switchable dielectric materials. This work represents a feasible strategy thought for the targeted harvesting of low temperature ferroelectrics.

Temperature‐Triggered Switchable Dielectric Constants in Zinc‐Based Hybrid Organic‐Inorganic Compounds: (C3H6NH2)2[ZnX4] (X = Cl and Br)

Two new zinc‐based hybrid organic‐inorganic compounds (AZT)2[ZnX4] (AZT = azetidine cation; X = Cl, 1; Br, 2) were successfully synthesized as high‐temperature stimuli‐responsive materials. Systematic thermodynamic characterization demonstrated that they undergo reversible structural phase transitions accompanied by switchable dielectric constant centered at 342 K for 1 and 356 K for 2, respectively. Variable‐temperature single‐crystal X‐ray analysis and dielectric constant measurements disclosed the order‐disorder transformation of the cation and anion contributed to the desirable electrical properties. As expected, the static‐motional transition in crystal structure arouses dielectric transitions between the low‐ and high‐dielectric states, making them a type of switchable dielectric materials.

Covalently Bonded Pillared Layered Bromoplumbate with High Thermal Stability: High Capacitance Gain after Photoinduced Electron Transfer.

Improving the stability and photoelectric properties are current aims in the field of inorganic-organic hybrid lead halides. In this work, a new covalently bonded pillared layered bromoplumbate, [Pb3Br6(CV)]n, was prepared using a photoactive zwitterion viologen, N,N'-4,4'-bipyridiniodipropionate (CV), as a ligand. It has a high thermal stability in air and shows a remarkable increase of capacitance after photoinduced electron transfer (PIET). The observed dielectric switch ratio of ∼689% at 3 kHz exceeded all reported values at room temperature for switchable dielectric materials. The capacitance gain was derived from the redistribution of electrons after PIET from the lead-halide layer to organic π-aggregates, so that the activation energy of hopping polarizability was significantly reduced.

A Semiconducting Organic–Inorganic Hybrid Metal Halide with Switchable Dielectric and High Phase Transition Temperature

Organic–inorganic hybrid metal halides with temperature-triggered responsive switchable dielectric properties have evoked great attention for their potential application in the field of optoelectronic information. Here, we present a new organic–inorganic hybrid metal halide switchable dielectric material, [(C3H5)2N(CH3)2]2SnCl6 (1), which is obtained by the reaction of diallyldimethylaminium chloride and tin(IV) chloride pentahydrate. Compound 1 exhibits excellent high-temperature switchable dielectric performance and antifatigue. Notably, 1 also exhibits multifunctionality with semiconducting and photoluminescence property. Such a Sn(IV)-based organic–inorganic hybrid with outstanding switchable dielectric, semiconducting, and photoluminescence characteristics will pave a new approach in the development of Sn(IV)-based metal halides with practical applications.

A high-temperature multiaxial precision time-delayed dielectric switch crystal triggered by linear/propeller/ball three-form motion

The new crystal motor with extraordinary thermal hysteresis turns out to be a multiaxial precision time-delayed dielectric switch.

All-organic room temperature thermally switchable dielectric system

Room temperature switchable dielectric materials have great potential in applications such as smart sensors, energy storage and circuit protection.

Phase transition and switchable dielectric behaviours in an organic–inorganic hybrid compound: (3-nitroanilinium) 2 (18-crown-6) 2 (H 2 PO 4 ) 2 (H 3 PO 4 ) 3 (H 2 O)

An organic–inorganic hybrid compound with an extensive three-dimensional (3D) crystal structure, (3-nitroanilinium)2(18-crown-6)2(H2PO4)2(H3PO4)3(H2O) (1), was synthesized under slow evaporation conditions. Differential scanning calorimetry measurements indicated that 1 underwent a reversible phase transition at ca 231 K with a hysteresis width of 10 K. Variable-temperature X-ray single-crystal diffraction revealed that the phase transition of 1 can be ascribed to coupling of pendulum-like motions of its nitro group with proton transfer in O–H···O hydrogen bonds of the 3D framework. The temperature dependence of its dielectric permittivity demonstrated a step-like change in the range of 150–280 K with remarkable dielectric anisotropy, making 1 a promising switchable dielectric material. Potential energy calculations further supported the possibility of dynamic motion of the cationic nitro group. Overall, our findings may inspire the development of other switchable dielectric phase transition materials by introducing inorganic anions into organic–inorganic hybrid systems.

Lead-Free Hybrid Material with an Exceptional Dielectric Phase Transition Induced by a Chair-to-Boat Conformation Change of the Organic Cation.

Hybrid organic-inorganic perovskite materials have demonstrated great potential in the field of photovoltaics and photoelectronics. On the basis of the high degree of structural flexibility and compatibility, diverse molecular functional materials have been assembled by modifying the length of the organic components and/or dimensionality of the inorganic frameworks. In this paper, we present a chiral lead-free organic-inorganic hybrid, (piperidinium)2SbCl5 (1), which follows the one-dimensional inorganic frameworks of the corner-sharing SbCl6 octahedra. Strikingly, 1 displays a dielectric phase transition at Tc = 338 K, changing from the chiral space group of P212121 to polar Pna21 upon heating. Crystal structure analyses reveal that an unusual thermally activated conformation change of the piperidinium cations affords the driving force to the phase transition of 1. That is, organic piperidinium moieties display a chairlike conformation below Tc, which transforms to a boatlike structure above Tc. Such an unprecedented change is strongly coupled to the dielectric transition along with notable steplike anomalies, which suggest that 1 could be used as a potential switchable dielectric material. Besides, the temperature-dependent conductivity and theoretical analysis of its electronic structure disclose the semiconducting behavior of 1. This study paves the pathway to the design of new lead-free semiconducting perovskites with targeted properties for optoelectronic application.

Room‐Temperature Dielectric Switchable Nanocomposites

Room‐temperature switchable dielectric materials are of interest for many applications, including solar energy storage, smart switches, automatic filters, and next‐generation sensors. Here, a temperature‐triggered dielectric switchable nanocomposite by dispersing octadecylamine‐grafted multiwalled carbon nanotubes (ODA‐MWCNTs, for short) into hexadecane is reported. The composite has low permittivity at molten state and high permittivity at frozen state, and the permittivity switch is triggered around 18 °C. The highest permittivity contrast ratio reaches 106.4 at 2.0% CNT volume fraction. The composite shows frequency‐sensitive and temperature‐ramping‐rate‐sensitive properties. Further investigation indicates that the permittivity switch is caused by the change of the ODA‐MWCNT percolating networks during phase transition.

Phase Transition Originating from Disorder–Order Transformation Coupled with Reorientation in the Organic–Inorganic Hybrid Compound (C4H14N2)[Cd2(H2O)6(SO4)3

The organic–inorganic hybrid compound 1,4‐butyldiammonium hexaaquadicadmium(II) trisulfate (C4H14N2)[Cd2(H2O)6(SO4)3] (1) was synthesized by the reaction of 3CdSO4·8H2O with 1,4‐butanediamine in sulfuric acid aqueous solution. Differential scanning calorimetry measurements indicate that 1 undergoes a reversible phase transition at 243.4 K with a thermal hysteresis of 3.3 K. Single‐crystal X‐ray diffraction data disclose that the phase transition is from the room‐temperature phase with the space group C2/c to the low‐temperature phase with the space group P1 with the Aizu notation of 2/mF1. The structural phase transition of 1 is ascribed to the coupling of disorder–order transformations of the flexible 1,4‐butyldiammonium cation and a sulfate anion and reorientation of the cation. The temperature dependence of the dielectric permittivity demonstrates a step‐like change in the range 200–260 K, which makes (C4H14N2)[Cd2(H2O)6(SO4)3] a promising switchable dielectric material. The results could offer an avenue to design switchable dielectric materials through the synergistic effect of disorder–order transitions and reorientation motion.

A supra-molecular switchable dielectric material with non-linear optical properties

A supra-molecular crystal, 1-[C6H13NH][18-crown-6][ClO4] monohydrate, has been reported to show reversible dielectric anomalies and nonlinear optical properties, which suggests that it could be conceived as the potential switchable dielectric and non-linear optical material.

Switchable dielectric phase transition originating from disorder–order transformation and distortion in {[(C4H4N2)Co(H2O)4]SO4·2H2O}n

Disorder–order transition of the SO42− and distortion of the [(C4H4N2)Co(H2O)4]2+ chain induce the phase transition of {[(C4H4N2)Co(H2O)4]SO4·2H2O}n.

Inorganic–organic hybrid switchable dielectric materials with the coexistence of magnetic anomalies induced by reversible high-temperature phase transition

We reported an inorganic–organic switchable dielectric hybrid, which shows the coexistence of magnetic responses as another potential physical channel to structural phase transition.