Reversible Solid-state Phase Transition Research Articles

Lead-Free Double Perovskite Semiconductor with Rigid Spacer-Induced High-Tc Dielectric Switch Features.

Layered hybrid perovskites possess exceptional semiconductor features and structural versality, making them viable candidates for developing multifunctional dielectric phase-transition materials (PTMS). However, most PTMs based on layered hybrid perovskites still suffer from Pb toxicity and low operating temperature. The recently developed hybrid double perovskites provide a new routine to designed PTMs with desired working performance and environment-friendly chemical compositions. Herein, using rigid aromatic cations as templates, we have successfully synthesized a novel double perovskite (benzylammonium)4 AgBiBr8 (1), which consists of corner-sharing AgBr6 and BiBr6 layers and benzylammonium cations. Notably, 1 exhibits a high-temperature first-order reversible solid-state phase transition at 383/387 K (cooling/heating) and switchable dielectric performance around the temperature. Compared with the soft organic chain version of the compound, the phase transition temperature of 1 shows a large enhancement of 99 K, validating the correctness of the designing strategy. In addition, 1 also exhibits semiconductor characteristics with a calculated bandgap of 2.34 eV and an optical bandgap of 2.29 eV. Remarkably, the single crystal photodetector of 1 shows a low dark current (2.12×10-13 A), a high on/off ratio (1.77×103 ), and a fast response (τrise =125 μs and τdecay =419 μs). Such a lead-free phase transition material combined with semiconductor properties provides a new strategy to develop environmentally friendly multifunctional materials.

Polymorphism of Cis-Unsaturated Fatty Acid Amide: Oleamide

The polymorphism of oleamide, an amide derivative of oleic acid, the most abundant naturally occurring cis-unsaturated fatty acid, was studied mainly by differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) using a high-purity sample. The melt-crystallized sample showed two reversible solid-state phase transitions, revealing three crystalline phases, A–C, in order from the low-temperature side. The three solid phases gradually transformed to another solid phase, D, by holding them below 35 °C; D reverted only to C when heated above 45 °C. The B → C reversible transition was accompanied by a large transition enthalpy amounting to about one-third of the heat of fusion of the C phase. A low-purity oleamide showed no polymorphism. The XRD profiles in the long-spacing region suggested that all four phases formed the segregated lamellar structure, in which the methyl and amide groups were separated.

Two Manganese(II)-Based Hybrid Multifunctional Phase Transition Materials with Strong Photoluminescence, High Quantum Yield, and Switchable Dielectric Properties: (C6NH16)2MnBr4 and (C7NH18)2MnBr4.

Multifunctional materials have always been an attractive research area, but how to combine multiple excellent properties in one compound remains a considerable challenge. Organic-inorganic hybrid compounds are widely used in the design of such materials due to their rich properties and flexible assembly. Herein, two new manganese(II)-based organic-inorganic hybrid compounds, (C6NH16)2MnBr4 (1) and (C7NH18)2MnBr4 (2), are prepared by the solution method. Compounds 1 and 2 both emit extremely strong green light under UV excitation, with high quantum yields of 45.93 and 50.98%, respectively. In addition, reversible solid-state phase transitions and obvious switchable dielectric properties are shown at 378/366 and 361/352 K, respectively. The coexistence of the dual stimulus-response characteristics of temperature and light in compounds 1 and 2 opens a new path for exploring more multifunctional phase transition materials.

H/F Substitution on the Spacer Cations Leads to 1D-to-2D Increment of the Pyrrolidinium-Containing Lead Iodide Hybrid Perovskites.

Hybrid organic-inorganic perovskites (HOIPs) have emerged as multifunctional materials with remarkable optical and electronic properties. In particular, 2D-layered lead iodide-based HOIPs possess great practical application potential in the photoelectric field. In this work, we report H/F substitution-induced 1D-to-2D increment of lead iodide HOIPs. The enantiomeric HOIPs, S- and R-FPPbI3 (FP = 3-fluoropyrrolidinium), were achieved by monofluoride substitution on the spacer cations of the parent HOIP, PyPbI3 (Py = pyrrolidinium), showing mirror image structural relationship and reversible solid-state phase transition. A 2D-layered HOIP, (DFP)2PbI4 (DFP = 3,3-difluoropyrrolidinium), was achieved with a low band gap of 2.09 eV through difluoride substitution, thanks to the expansion of the Pb-I network from 1D to 2D. This work highlights the exploration of 1D chiral and 2D-layered HOIP materials with reversible phase transitions through H/F substitution strategies.

(C7H18N2)PbI4: A 2D Hybrid Perovskite Solid-State Phase Transition Material with Semiconducting Properties.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) have gained attention as a result of their flexibility and adjustability of the structure. However, the large band gap of two-dimensional perovskites limits their application in the photoelectric field. In the present work, we report a two-dimensional organic-inorganic hybrid compound of (C7H18N2)PbI4 (1) with a narrow band gap, which consists of [PbI4]2-n layers and N-(2-aminoethyl)piperidinium cations. 1 exhibits semiconducting properties with a narrow optical band gap of ∼2.02 eV and a photoelectric response with a ratio of photocurrent to dark current of ∼100. In addition, it exhibits a reversible solid-state phase transition at 228 K. This finding should inspire research into more 2D layered OIHPs with the combination of phase transition and semiconductor properties.

Reversible solid-state phase transitions in confined two-layer colloidal crystals

Using a combination of fluorescence and bright-field optical imaging, the solid-state packing structures of semi-confined two-layer spherical colloidal crystals were observed during modulation of an external AC electric field. Upon increasing field strength, the bottom layer of colloids (layer 1) transitioned from the entropically favored hexagonal packing structure with p6m symmetry to a square-packing structure with p4m symmetry. The packing structure of layer 2 was determined by the packing structure of layer 1, with layer 2 particles resting in, and moving in registry with, the low-energy interstitial sites of layer 1. Modulation of the field strength thus resulted in a reversible transition between a face-centered cubic crystal structure and a body-centered cubic crystal structure at low and high field strengths, respectively. These structures were found to be sensitive to the particle density in the wells, with vacancies and insertions leading to the formation of mixed crystal phases at high field strengths.

Reversible Solid-State Phase Transitions between Au-P Complexes Accompanied by Switchable Fluorescence.

Six complexes {(3-bdppmapy)(AuCl)2}n (1-6; 3-bdppmapy = N,N'-bis(diphenylphosphanylmethyl)-3-aminopyridine and tht = tetrahydrothiophene) were simultaneously formed by the reaction of Au(tht)Cl and 3-bdppmapy in CH2Cl2 followed by infusion with hexane. Complexes 4-6 could be produced independently by volatilizing solvent in air, solid-state heating, or solvothermal reaction. The PPh2-Au-Cl moieties extended in different directions, forming Au-Au and Au-Au-Au interactions. Complex 4 could be converted to 5 by heating to 130 °C, with the cleavage of one Au-Au bond, while 5 reverted back to 4 upon exposure to CH2Cl2 vapor over 11 h. This solid-state phase transition could be recycled and was accompanied by a change in solid-state fluorescence, without obvious intensity decay over five cycles. The reason for both the phase transition and difference in photoluminescence is related to the different numbers and strengths of aurophilic interactions in each complex that could be modeled by density functional theory calculations.

C6N2H18][SbI5]: A Lead-free Hybrid Halide Semiconductor with Exceptional Dielectric Relaxation.

[C6N2H18][SbI5] (1), a novel metal halide semiconductor with dielectric relaxation behavior, has been successfully synthesized, in which the cavities between the one-dimensional [SbI5] n2- polyanions are occupied by 2-methyl-1,5-pentanediammonium (2-MPDA) cations. 1 undergoes a reversible solid-state phase transition at TC = 192.7 K and shows a step-like dielectric anomaly. Interestingly, above TC, distinct dielectric dispersion in a wide temperature range is also witnessed. Remarkably, the solid state UV-vis diffuse reflectance spectrum of 1 exhibits a slightly gentler absorption edge at about 650 nm; that is, 1 adopts an indirect band gap with 1.92 electron volts. The combined narrow band gap, strong photoconductivity effect, and excellent dielectric relaxation might shed light on the exploitation of lead-free hybrid metal halide molecular materials with promising application prospects in thermoresponsive relaxation-type dielectric materials and photovoltaic conversion devices.

A temperature-triggered triplex bistable switch in a hybrid multifunctional material: [(CH2)4N(CH2)4]2[MnBr4

Bistable optical-electrical duplex switches represent a class of highly desirable intelligent materials because of their potential applications in the fields of next-generation flexible devices. However, controllable photoelectric switchable materials with high-performance dielectric-switching and optical-switching properties are still scarce, with triplex bistable switches being rarely reported. Herein, a novel optoelectronic triple-functional organic-inorganic material, 5-azonia-spiro[4,4]nonane tetrabromomanganese (1, [ASN]2[MnBr4], ASN = (CH2)4N(CH2)4), which undergoes a reversible solid-state phase transition around 327 K and exhibits a recognizable second harmonic generation (SHG) effect between SHG-on and SHG-off states, has been successfully synthesized and grown as block crystals. Intriguingly, the bromine-doped crystal can exhibit intense green luminescence with a high quantum yield of 13.07% under UV excitation, extending its application in the field of photoelectric seamless integration and/or flexible multifunctional devices.

The Rich Solid-State Phase Behavior of dl-Aminoheptanoic Acid: Five Polymorphic Forms and Their Phase Transitions.

The rich landscape of enantiotropically related polymorphic forms and their solid-state phase transitions of dl-2-aminoheptanoic acid (dl-AHE) has been explored using a range of complementary characterization techniques, and is largely exemplary of the polymorphic behavior of linear aliphatic amino acids. As many as five new polymorphic forms were found, connected by four fully reversible solid-state phase transitions. Two low temperature forms were refined in a high Z′ crystal structure, which is a new phenomenon for linear aliphatic amino acids. All five structures consist of two-dimensional hydrogen-bonded bilayers interconnected by weak van der Waals interactions. The single-crystal-to-single-crystal phase transitions involve shifts of bilayers and/or conformational changes in the aliphatic chain. Compared to two similar phase transitions of the related amino acid dl-norleucine, the enthalpies of transition and NMR chemical shift differences are notably smaller in dl-aminoheptanoic acid. This is explained to be a result of both the nature of the conformational changes and the increased chain length, weakening the interactions between the bilayers.

Unusual two-step sequential reversible phase transitions with coexisting switchable nonlinear optical and dielectric behaviors in [(CH3)3NCH2Cl]2[ZnCl4

[(CH3)3NCH2Cl]2[ZnCl4] is a novel switchable nonlinear optical and switchable dielectric compound, which undergoes two reversible solid state phase transitions.

Dielectrophoretic assembly of dimpled colloids into open packing structures.

Reversible solid-state phase transitions between open- and close-packed structures in two-dimensional colloidal crystals comprising 1.8 μm dimpled spherical colloids were observed using negative dielectrophoresis. These asymmetrically-shaped colloids adopted lattices with cmm plane group symmetry and a packing fraction, ϕ, of 0.68 at low electric field strengths. At high electric field strengths, the close-packed p6m symmetry was observed, with ϕ = 0.90. The transition between open and close-packed structures was found to be reversible, depending on the applied electric field strength and frequency. Finite Fourier transform analysis and COMSOL simulations revealed the existence of repulsive interactions between colloids perpendicular to the electric field lines due to a concentration of the electric field at the edges of the dimpled regions of the colloids. The repulsive interactions resulted in a stretching of the hexagonal lattice perpendicular to the electric field lines, the magnitude of which depended on the electric field strength. By screening the colloids from the electric field in local potential wells, the entropically favored close-packed hexagonal lattice with ϕ = 0.91 was recovered.

Solid-state phase transition induced by ordering of flexible chain alkylamine in N-ethyl-n-butylammonium 3, 5-dinitrobenzoate monohydrate

A new molecule-based compound, N-ethyl-n-butylammonium 3, 5-dinitrobenzoate monohydrate, which undergoes a reversible solid-state phase transition at 197K (Tc), has been successfully constructed based on long-chain alkylamine. Specific heat capacity and differential scanning calorimetry (DSC) measurements confirm that it is first-order phase transition with a 5K thermal hysteresis between heating and cooling scans. Dielectric constants exhibit distinct anomalies around Tc accompanied with step-like responses between low and high dielectric states, which further confirm the phase transition. Variable-temperature single-crystal X-ray diffraction analyses illustrate that the phase transition was elucidated from ordering of the flexible N-ethyl-n-butylammonium cations coupled with reorientational motion of the alkylamine chain.

Structure-Triggered High Quantum Yield Luminescence and Switchable Dielectric Properties in Manganese(II) Based Hybrid Compounds.

Two new manganese(II) based organic-inorganic hybrid compounds, C11H21Cl3MnN2 (1) and C11H22Cl4MnN2 (2), with prominent photoluminescence and dielectric properties were synthesized by solvent modulation. Compound 1 with novel trigonal bipyramidal geometry exhibits bright red luminescence with a lifetime of 2.47 ms and high quantum yield of 35.8 %. Compound 2 with tetrahedral geometry displays intense long-lived (1.54 ms) green light emission with higher quantum yield of 92.3 %, accompanied by reversible solid-state phase transition at 170 K and a distinct switchable dielectric property. The better performance of 2 results from the structure, including a discrete organic cation moiety and inorganic metal anion framework, which gives the cations large freedom of motion.

A Switchable Molecular Dielectric with Two Sequential Reversible Phase Transitions: [(CH3)4P]4[Mn(SCN)6

A new organic-inorganic hybrid switchable and tunable dielectric compound, [(CH3)4P]4[Mn(SCN)6] (1), exhibits three distinct dielectric states above room temperature and undergoes two reversible solid-state phase transitions, including a structural phase transition at 330 K and a ferroelastic phase transition with the Aizu notation of mmmF2/m at 352 K. The variable-temperature structural analyses disclose that the origin of the phase transitions and dielectric anomalies can be ascribed to the reorientation or motion of both the [(CH3)4P](+) cations and [Mn(SCN)6](4-) anions in solid-state crystals.

Sequential structural transitions with distinct dielectric responses in a layered perovskite organic-inorganic hybrid material: [C4H9N]2[PbBr4

A novel organic-inorganic hybrid layered perovskite-type compound of the general formula A2BX4, bis(IBA)tetrabromolead(II) (1, IBA = isobutyl-ammonium cation), has been successfully synthesized and grown as flake-like crystals, and undergoes two reversible solid-state phase transitions at 315 K and 250 K, and has been systematically characterized using differential scanning calorimetry measurements, variable-temperature structural analyses, variable-temperature powder X-ray diffraction measurements and dielectric measurements. 1 exhibits a remarkable temperature-dependent dielectric behavior, which could be switched between high and low dielectric states above room temperature, and a broad peak exists below room temperature. The most striking dielectric property is the remarkable anisotropy along the various crystallographic axes. All of these demonstrate its potential application as a high temperature switchable molecular dielectric and low temperature phase transition material.

Massive Anisotropic Thermal Expansion and Thermo‐Responsive Breathing in Metal–Organic Frameworks Modulated by Linker Functionalization

AbstractFunctionalized metal–organic frameworks (fu‐MOFs) of general formula [Zn2(fu‐L)2dabco]n show unprecedentedly large uniaxial positive and negative thermal expansion (fu‐L = alkoxy functionalized 1,4‐benzenedicarboxylate, dabco = 1,4‐diazabicyclo[2.2.2]octane). The magnitude of the volumetric thermal expansion is more comparable to property of liquid water rather than any crystalline solid‐state material. The alkoxy side chains of fu‐L are connected to the framework skeleton but nevertheless exhibit large conformational flexibility. Thermally induced motion of these side chains induces extremely large anisotropic framework expansion and eventually triggers reversible solid state phase transitions to drastically expanded structures. The thermo‐responsive properties of these hybrid solid–liquid materials are precisely controlled by the choice and combination of fu‐Ls and depend on functional moieties and chain lengths. In principle, this combinatorial approach allows for a targeted design of extreme thermo‐mechanical properties of MOFs addressing the regime between crystalline solid matter and the liquid state.

On the coexistence of copper–molybdenum bronzes: CuxMoO3 (0.2<x<0.25; typically x∼0.23) and CuyMoO3−z (0.1<y<0.2; typically y∼0.15) in the Cu–MoO2–O quasi-ternary system

Two copper-molybdenum bronzes: Cu{sub y}MoO{sub 3-z} (0.1 < y < 0.2; typically y {approx} 0.15) and Cu{sub x}MoO{sub 3} (0.2 < x < 0.25; typically x {approx} 0.23) were prepared as glistening black polycrystalline materials by the solid state reaction of Cu and MoO{sub 3} at 600 {sup o}C under argon in Pt crucibles. Powder XRD showed that the material with global composition '0.1Cu.MoO{sub 3}' comprises {approx}Cu{sub 0.15}MoO{sub 3} and MoO{sub 3}; whilst '0.2Cu.MoO{sub 3}' comprises {approx}Cu{sub 0.15}MoO{sub 3} and {approx}Cu{sub 0.23}MoO{sub 3}. DTA performed on '0.2Cu.MoO{sub 3}' reveals a reversible solid state phase transition {approx}520 {sup o}C under argon. Reacting equimolar amounts of Cu{sub 2}O and MoO{sub 2} at 600 {sup o}C in a Cu crucible under argon yields: Cu{sub 6}Mo{sub 5}O{sub 18}, Cu and MoO{sub 2}. A tentative subsolidus Cu-MoO{sub 2}-O isothermal ({approx}25 {sup o}C) phase diagram under argon is drawn from these data. Oxidation states of Cu and Mo within this system are discussed.

Nanotech surface networks get functionalized

A new molecule-based compound, N-ethyl-n-butylammonium 3, 5-dinitrobenzoate monohydrate, which undergoes a reversible solid-state phase transition at 197 K (Tc), has been successfully constructed based on long-chain alkylamine. Specific heat capacity and differential scanning calorimetry (DSC) measurements confirm that it is first-order phase transition with a 5 K thermal hysteresis between heating and cooling scans. Dielectric constants exhibit distinct anomalies around Tc accompanied with step-like responses between low and high dielectric states, which further confirm the phase transition. Variable-temperature single-crystal X-ray diffraction analyses illustrate that the phase transition was elucidated from ordering of the flexible N-ethyl-n-butylammonium cations coupled with reorientational motion of the alkylamine chain.

Solid-state13C NMR Study on Order → Disorder Phase Transition in Oleic Acid

The reversible solid-state phase transition between the y and a phases of oleic acid was followed by 1 3 C solid-state NMR spectroscopy. All peaks in the y and α phases were assigned based on the corresponding crystal structures determined by X-ray diffraction method (Abrahamsson and Ryderstedt-Nahringbauer, 1962, and Kaneko et al., 1996). As to the transition behavior, there was a significant difference between the two hydrocarbon chains straddling cis-olefin group. On the y → α phase transition at 271 K, the methyl-sided methylene carbons exhibited upfield shifts due to the gauche effect. Characteristic peaks shifts due to the conformational change of the cis-olefin group were observed for cis-olefin carbons. On the other hand, the peaks due to carboxyl-sided chains showed no large shifts on this transition. Each oleic acid carbon atom showed a discontinuous decrease in T 1 , except for the methyl carbon, which was in the extreme narrowing limit even in the γ phase. However, the T 1 values of the methyl-sided carbons were significantly smaller than those of the carboxyl-sided carbons in the a phase. The conformational disordering in the methyl-sided chains was accompanied by a remarkable increase of molecular motion in this moiety.