Low Transition Temperature Research Articles

Low-temperature polymorphic transition in highly compressed uranium dioxide

The Mayer group expansion method is extended on the low-temperature solids where quantum effects cannot be ignored and applied to the prediction of polymorphic transition line between cubic Fm3m and orthorhombic Pnma phases in the highly compressed ionic crystal of uranium dioxide. The temperature dependence of the transition pressure and volume changes are evaluated and the results are compared with existing experimental data and ab initio predictions.

Detailed pathway for a fast low-temperature synthesis of strongly thermochromic W-doped VO2 films with a low transition temperature

We report the discharge characteristics, and population of chosen atomic neutral (V, O and Ar) and ionic (V+, V2+, O+ and Ar+) species in the discharge during low-temperature (350 °C) depositions of W-doped VO x films onto a 170 nm thick Y-stabilized ZrO2 layer on a 1 mm thick conventional soda-lime glass. The depositions were performed using reactive deep oscillation magnetron sputtering with a pulsed O2 flow control and to-substrate O2 injection into a high-density plasma in front of the sputter V-W target. The pre-selected critical values of the oxygen partial pressure were in the range from 82 mPa to 92 mPa. Optical emission spectroscopy proved a relatively high density of O atoms in front of the substrate, which is important for production of the W-doped VO2 films. It was found that setting of the amount of O2 in the gas mixture determines not only the elemental and phase composition of the films and their deposition rate but also the crystallinity of the thermochromic VO2 phase in them. The crystalline W-doped VO2 films with a low transition temperature of 28 °C exhibited a high modulation of the solar energy transmittance of 8.9%. The results are important for further improvement of this new scalable sputter deposition technique for a fast (53 nm min−1 at a target-substrate distance of 100 mm in this work) low-temperature synthesis of high-performance durable thermochromic VO2-based multilayer coatings designed for smart-window applications.

New insights into the effect of glass addition on the piezoelectric and thermal stability properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 Pb-free ceramic by defect engineering of MPB

Lead-free piezoceramics with superior piezoelectric properties don't meet the requirements of practical applications due to their lower phase transition temperature and poor thermal stability. In the present work, we report a new insight into the effect of glass phase on the piezoelectric, Curie temperature and thermal stability of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCZT) ceramic. Unlike traditional glass materials with more than 80% of B2O3 and SiO2 as glass formers, our approach is to fabricate a glass phase (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-0.05B2O3 (abbreviate BBCZT) with the same elements and concentrations as the ceramic phase. The ceramics-doped glass samples with the composition [(1-x)BCZT-xBBCZT], where x=(0.0, 0.025, 0.05, 0.075 and 0.1 wt%), were sintered according to the glass phase content. The effect of BBCZT glass composition on the crystal structure, dielectric, ferroelectric and piezoelectric properties of BCZT was investigated in detail. X-ray diffraction revealed that the addition of glass phase causes a defect engineering of the tricritical triple point of BCZT ceramic, where the tetragonal (T) and rhombohedral (R) phases were suppressed by the addition of glass phase and the T-phase has completely vanished at x = 0.05. The maximum value of permittivity (ε = 4102) and converse piezoelectric coefficient (d*33 = 1150 Pm/V) were achieved for the 0.975BCZT-0.025BBCZT sample at ambient temperature. Furthermore, the diffusion coefficient (γ) and Curie temperature (Tc) were observed to increase beyond x = 0.025, indicating enhanced thermal stability of BCZT at high glass content. These results qualify that the addition of (BBCZT) can enhance piezoelectric properties, phase transition temperature and thermal stability of BCZT ceramic which can meet wide requirements of practical applications.

A Stable and Self‐Healing Thermochromic Polymer Coating for All Weather Thermal Regulation

AbstractEnergy‐free thermal regulation is in great demand nowadays. Thermochromic materials are widely explored and used in smart windows. However, most thermochromic materials have fixed transition temperature and still suffer from poor stability. To overcome this challenge, a thermochromic polymer coating based on ion–dipole interaction with switchable transition temperature, high stability toward several harsh environments, self‐healing, and radiative cooling property is developed. It can continuously tune from transparent to opaque according to the temperature change. The lower critical transition temperature can be tuned from 33 to 43 °C by simply adjusting the composition of ionic liquids. Owing to the fluorine polymer backbone and dynamic ion–dipole interactions, it can also keep stable in aquatic, −20 °C, and 70 °C environments and self‐heal upon damage thus prolonging its working life for real applications.

Nickel-Imidazolium Low Transition Temperature Mixtures with Lewis-Acidic Character.

Low transition temperature mixtures (LTTMs) are a new generation of solvents that have found extensive application in organic synthesis. The interactions between the components often generate highly activated, catalytically active species, thus opening the possibility of using LTTMs as catalysts, rather than solvents. In this work, we introduce a nickel-based imidazolium LTTM, study its thermal behavior and explore its catalytic activity in the solvent-free allylation of heterocycles with allylic alcohols. This system is effective in this reaction, affording the corresponding products in excellent yield without the need for additional purifications, thus resulting in a very environmentally friendly protocol.

Achieving enhanced ferroelectricity and piezoelectric responses in 〈0 0 1〉-textured KNN-BCZT ceramics with BaTiO3 microplates as template

Potassium sodium niobate (KNN) as a typical lead-free piezoelectric ceramic has higher Curie temperature, but its piezoelectric constant is not high enough at room temperature. The introduction of BCZT with high piezoelectric responses into KNN is an important strategy to improve its piezoelectric properties. Moreover, orientation engineering is also a significant method to enhance piezoelectric responses of KNN-based ceramics. Herein, 〈001〉 crystallographic texture in KNN-BCZT ceramics was realized though templated grain growth method with BaTiO3 microplates as template, and the textured sample exhibited superior ferroelectric and piezoelectric properties (2Pr = 43.5μC/cm2, d33*=137 pm/V, d33 = 190 pC/N, kp = 0.54) and lower phase transition temperatures (TO-T = 170.2 °C, TC = 388.3 °C) than randomly oriented sample. This work provides a good strategy to design KNN-based lead-free ceramics with superior piezoelectric properties by constructing solid solution system and controlling crystallographic orientation.

Mechanistic Investigation of Isobutanol/Isobutyl Acetate Separation by Extraction Using Low-Transition Temperature Mixtures

Mechanistic Investigation of Isobutanol/Isobutyl Acetate Separation by Extraction Using Low-Transition Temperature Mixtures

Solid-phase extraction combined with dispersive liquid-liquid microextraction for the analysis of glucocorticoids in environmental waters using liquid chromatography-tandem mass spectrometry

This paper illustrates an enrichment procedure based on the combination of solid phase extraction (SPE) with dispersive liquid-liquid microextraction (DLLME) for the determination of ng/L concentration levels of glucocorticoids in river water samples. In SPE-DLLME, the target analytes were adsorbed by loading a large volume sample (200 mL) into an OASIS HLB cartridge (60 mg). After their desorption with a small volume of ethyl acetate (500 µL), this eluate was used as the dispersant in the following DLLME, performed on 5 mL of water, using a low transition temperature mixture (LTTM) as the extractant (100 µL). The LTTM was obtained by the heat-mixing of choline chloride and sesamol in a molar ratio 1:3 (ChCl:Ses, 1:3); when cooled, it was liquid at room temperature, denser than water and immiscible with it. The SPE-DLLME approach significantly limits the use of high volumes of organic solvents, avoids the evaporation step, and allows one to achieve an enrichment factor greater than 2500. All extracts were analysed by high-performance liquid chromatography-electrospray-tandem mass spectrometry. Eleven glucocorticoids, including the epimers dexamethasone/betamethasone, were separated on a polysaccharide-based column, based on cellulose tris(3‑chloro-4-methylphenylcarbamate) chiral selector. Recoveries ranged from 68 to 100% (spike level of 5 and 20 ng/L), with a LOD of 0.21-1.39 ng/L and a LOQ of 0.69-4.17 ng/L. The intra-day precision and inter-day precision were lower than 15%. After optimization and complete validation, the method was applied to analyze surface water samples, taken from River Tiber, to evaluate the effective applicability of the procedure and to establish the contamination levels for these substances.

Synthesis, structure, and physical properties of a Y–Au-Ge 1/1 Tsai-type quasicrystal approximant and Y14(Au,Ge)51 with the Gd14Ag51 structure type

Exploration of the Au–Ge rich part of the pseudo-binary section Yx(Au0.70Ge0.30)100-x (3 < x < 18) in the Y–Au-Ge system afforded the intermetallic compounds Y3(Au0.7054Ge0.2946)19-x (x ≈ 0.38) and Y14(Au0.8313Ge0.1687)51, which are new representatives of the cubic 1/1 Tsai-type approximant crystal (YbCd6 parent type, space group Im3‾.) and the hexagonal Gd14Ag51 structure type (space group P6/m), respectively. Y3(Au0.7054Ge0.2946)19-x decomposes peritectically into Y14(Au,Ge)51 phase and melt at around 700 °C. In this respect the Y–Au-Ge system deviates from the Y–Au–Si system which firstly contains a second type of 1/1 approximant crystal phase with higher Y content, Y3.25(Au,Si)18-x (x ≈ 0.11) and, secondly, adjacent at higher Y composition there is a stoichiometric and ordered tetragonal phase YAu3Si. Y3(Au,Ge)19-x and Y14(Au,Ge)51 exhibit bulk superconductivity of conventional type-II BCS type albeit with very low transition temperatures (below 1 K), which is very similar to the corresponding compounds in the Y–Au–Si system.

Unexpected self-assembly of carbon dots during digital light processing 3D printing of vanillin Schiff-base resin

Bio-based and recyclable composite thermosets were obtained through digital light processing (DLP) 3D printing by dispersing cellulose-derived carbon dots (CDs) in a photocurable vanillin Schiff-base resin. The exposure of CDs to DLP induced a partial reduction of the oxygen functionalities and a self-assembly of CDs into micrometric fibers embedded in the thermoset matrix. A comparison with the vanillin Schiff-base thermoset, illustrated lower transition temperature from the glassy to the rubbery state and inferior shape memory properties for the CD containing thermoset. This is ascribed to a lower crosslinking density due to the replacement of the covalent interactions of the thermosets with supramolecular interactions generated inside the microfibers and between the microfibers and the surrounding matrix. This can also explain the inferior mechanical rigidity of the composites with respect to the single component thermosets. However, the supramolecular interactions endow the composites with better mechanical and chemical recyclability with an almost complete preservation of the original mechanical properties.

High configurational entropy for low phase transition temperature and thermal expansion of A2M3O12 oxide ceramics

Transverse vibrations of bridging atoms in framework structure oxides contribute to negative thermal expansion (NTE), increasing the configurational entropy. Herein, the configurational entropy of NTE (Al1/3Fe1/3Cr1/3)2Mo3O12 (AFCM) is tuned by introducing ZrMg and W to AlFeCr and Mo sites to lower NTE. The NTE of ((Zr1/2Mg1/2)x(Al1/3Fe1/3Cr1/3)(1-x))2Mo3O12 (ZMAFCM) reduce obviously with increasing the content of ZrMg and also the phase transition temperatures (PTTs) (x = 0∼0.5). For ((Zr1/2Mg1/2)x(Al1/3Fe1/3Cr1/3)(1-x))2(Mo1/2W1/2)3O12 (ZMAFCMW), the NTE and PTTs reduce at a faster rate than that of ZMAFM. The configurational entropy increases with the content of ZrMg firstly (x = 0∼0.4) and then decreases. The possible mechanism of thermal expansion change is related to the enhanced lattice configuration, high entropy. The inconsistent transverse vibrations of bridging oxygen atoms could reduce their contribution to NTE, especially for high entropy. The PTT of high configurational entropy oxides is reduced obviously due to the influenced on the effective electronegativity. The investigation paves a high entropy way to lower thermal expansion and PTT of A2M3O12 oxide ceramics and explores the further mechanism of NTE.

Near room temperature tunability of thermochromic VO2 thin films prepared via thermal oxidation method, influence of CO2:N2 gas flux ratios

In this study, we have investigated the thermochromic characterizations of VO2 thin films synthesized by the thermal oxidation method. The oxidation process of a DC sputtered metallic vanadium layer on glass substrates, at 450 °C for 1 h, was carried out in the presence of CO2:N2 gases with different flux ratios of 30:70, 40:60, 50:50, 60:40, and 70:30, respectively. Using CO2, as the oxidizing gas, provides an easy control route for obtaining the VO2 phase among various vanadium oxide phases. The layers were characterized by FESEM, XRD & Raman spectra, sheet resistance vs. temperature (20–120 °C), and UV–Vis–NIR spectra at 25 and 90 °C. The XRD and Raman spectra confirmed all prepared layers have a VO2 polycrystalline structure in monoclinic phase. We found among the studied samples CN30-70 and CN50-50 having desirable optical characteristics of peak visible transmittance of about 55%, with low transition temperatures (Tcr) of ∼42 and 31 °C, and also relatively high amounts of ΔT1700nm, ΔTsol and Tlum,av are good candidates for thermochromic smart windows, both from optical properties and economical fabrication method points of view.

Toolbox of Advanced Atomic Layer Deposition Processes for Tailoring Large-Area MoS2 Thin Films at 150 °C.

Two-dimensional MoS2 is a promising material for applications, including electronics and electrocatalysis. However, scalable methods capable of depositing MoS2 at low temperatures are scarce. Herein, we present a toolbox of advanced plasma-enhanced atomic layer deposition (ALD) processes, producing wafer-scale polycrystalline MoS2 films of accurately controlled thickness. Our ALD processes are based on two individually controlled plasma exposures, one optimized for deposition and the other for modification. In this way, film properties can be tailored toward different applications at a very low deposition temperature of 150 °C. For the modification step, either H2 or Ar plasma can be used to combat excess sulfur incorporation and crystallize the films. Using H2 plasma, a higher degree of crystallinity compared with other reported low-temperature processes is achieved. Applying H2 plasma steps periodically instead of every ALD cycle allows for control of the morphology and enables deposition of smooth, polycrystalline MoS2 films. Using an Ar plasma instead, more disordered MoS2 films are deposited, which show promise for the electrochemical hydrogen evolution reaction. For electronics, our processes enable control of the carrier density from 6 × 1016 to 2 × 1021 cm-3 with Hall mobilities up to 0.3 cm2 V-1 s-1. The process toolbox forms a basis for rational design of low-temperature transition metal dichalcogenide deposition processes compatible with a range of substrates and applications.

CO2 absorption enhancement in low transition temperature mixtures-based nanofluids: Experiments and modeling

The enhancement of gas–liquid mass transfer in the CO2 absorption process by Low Transition Temperature Mixtures (LTTMs) based nanofluids was investigated. The effects of loading and size of TiO2 nanoparticles on the CO2 absorption rate were studied experimentally. The absorption rate was found to be improved significantly after adding nanoparticles. The maximum enhancement factor of 1.35 was observed when using nanoparticles with a particle size of 10 nm and a concentration of 0.6 kg/m3. The maximum absorption enhancement factor and mass transfer coefficient were observed when the loading of nanoparticles increased, hence there was an optimal concentration of TiO2 nanoparticles in the CO2 absorption process. For the size of nanoparticles, the CO2 absorption rate was higher when the diameter of nanoparticles decreased. Furthermore, a three-dimensional unsteady mathematical model of gas–liquid mass transfer, which was based on the mechanisms of grazing effect and hydrodynamic effect in the gas–liquid boundary layer, was developed to describe the CO2 absorption enhancement. The model predictions were well consistent with the experimental results, with a maximum deviation of less than 5%, which proved the reliability of the model. Finally, Molecular dynamics simulations were conducted on the absorbent-CO2 system. The results showed that the addition of TiO2 nanoparticles led to a reduction in the simulation box size at the same simulation time, but it did not significantly alter the interaction between LTTMs and CO2. Therefore, it can be inferred that TiO2 nanoparticles enhance CO2 absorption capacity by modifying the mass transfer rate. Through the aforementioned study, this paper explores the experimental and mechanistic aspects of nanoparticle-enhanced absorption of CO2 in LTTMs systems. The research demonstrates the feasibility of nanoparticle-enhanced absorption of CO2 in LTTMs solvents, providing insights into studying nanoparticle-enhanced gas–liquid mass transfer and offering a new research approach for CO2 capture.

Preparation and Properties of Polysaccharide‐Based Epoxy Vitrimers

AbstractTraditional chemically cross‐linked polymer materials may cause severe environmental pollution and economic losses due to the difficulty of recycling. Vitrimers containing reversible dynamic covalent bonds are processable, recyclable, and self‐healing. In this article, a bio‐based epoxy resin curing agent is synthesized by hydrolysis using cellulose as raw material. The results show that the epoxy vitrimers with the best ratio have a lower topological transition temperature and a fast relaxation time at 140 °C. After soaking in solvent for 90 days, the gel content of the material is greater than 81%. The glass transition temperature of the sample measured by differential scanning calorimetry （DSC) is 83 °C. It also has a high initial decomposition temperature (350 °C) with good flexibility and solvent resistance, showing its good performance as a coating paint.

Microcalorimetry reveals multi-state thermal denaturation of G. stearothermophilus tryptophanyl-tRNA synthetase.

Mechanistic studies of Geobacillus stearothermophilus tryptophanyl-tRNA synthetase (TrpRS) afford an unusually detailed description-the escapement mechanism-for the distinct steps coupling catalysis to domain motion, efficiently converting the free energy of ATP hydrolysis into biologically useful alternative forms of information and work. Further elucidation of the escapement mechanism requires understanding thermodynamic linkages between domain configuration and conformational stability. To that end, we compare experimental thermal melting of fully liganded and apo TrpRS with a computational simulation of the melting of its fully liganded form. The simulation also provides important structural cameos at successively higher temperatures, enabling more confident interpretation. Experimental and simulated melting both proceed through a succession of three transitions at successively higher temperature. The low-temperature transition occurs at approximately the growth temperature of the organism and so may be functionally relevant but remains too subtle to characterize structurally. Structural metrics from the simulation imply that the two higher-temperature transitions entail forming a molten globular state followed by unfolding of secondary structures. Ligands that stabilize the enzyme in a pre-transition (PreTS) state compress the temperature range over which these transitions occur and sharpen the transitions to the molten globule and fully denatured states, while broadening the low-temperature transition. The experimental enthalpy changes provide a key parameter necessary to convert changes in melting temperature of combinatorial mutants into mutationally induced conformational free energy changes. The TrpRS urzyme, an excerpted model representing an early ancestral form, containing virtually the entire catalytic apparatus, remains largely intact at the highest simulated temperatures.

Skin Barrier Fine Tuning through Low-Temperature Lipid Chain Transition

The lipids in the mammalian stratum corneum (SC) adopt an unusually rigid arrangement to form a vital barrier preventing water loss and harmful environmental impacts. Just above the physiological temperature, a subset of barrier lipids undergoes a phase transition from a very tight orthorhombic to a looser hexagonal arrangement and vice versa. The purpose of this lipid transition in skin physiology is unknown. Permeability experiments on isolated human SC indicated that the transition affects the activation energy for a model compound that prefers lateral movement along lipid layers but not for water or a large polymer that would cross the SC through the pore pathway. The orthorhombic phase content of SC lipids, as determined by infrared spectroscopy, was also modulated by (de)hydration. Spontaneous rearrangement of human SC lipid monolayers into 10 nm higher multilamellar islets at 32-37 °C but not at room temperature was revealed by atomic force microscopy. Our findings add to our knowledge of fundamental skin physiology suggesting a fine temperature- and hydration-controlled switch from fluid lipids (required for lipid barrier assembly) to rigid and tightly packed lipids in the mature SC (necessary for the water and permeability barriers).

Ordered L10-FeNi (111) epitaxial thin film on Al2O3 (0001) substrate: Molecular beam epitaxy growth and characterizations

Ordered hard magnetic L10-FeNi has attracted attention as a candidate for rare-earth-free permanent magnet with a large maximum magnetic energy product. Fabricating L10-FeNi is a big challenge using conventional methods due to its low order-disorder transition temperature, 320 °C. In this work, high-quality ordered L10-FeNi films were fabricated by using molecular beam epitaxy directly on Al2O3 (0001) substrate with a two-step co-deposition method below 250 °C. The films were epitaxially grown with [111] orientation, confirmed by reflection high energy electron diffraction and x-ray diffraction patterns. An order-disorder phase transition at 320 °C was observed in temperature dependent electrical resistivity curve. The two-step molecular beam epitaxy grown film exhibited high uniaxial magnetic anisotropy constant, Ku, up to 1.15 × 106 J/m3. The obtained Ku value is comparable to previous result for FeNi along [100] growth direction, indicating an isotropic Ku. This work provides an effective molecular beam epitaxy growth method of high-quality ordered L10-FeNi (111) film for the development of the next-generation rare-earth-free permanent magnet.

Room-Temperature Ferromagnetism in Layered Mn-Substituted MoS2

Intrinsically two-dimensional (2D) ferromagnetic materials normally exhibit a low transition temperature, above which they would lose their magnetic properties. This makes it difficult to develop them for practical applications. Substituting transition metal atoms into 2D systems provides a straightforward way for achieving room-temperature ferromagnetism. Here, we propose a one-step chemical vapor deposition method to prepare Mn-substituted MoS2 monolayers, which exhibit robust magnetism, as confirmed by a combined study of physical property measurement systems and magneto-optical measurements. High-resolution transmission electron microscopy, Raman signals, and X-ray photoelectron spectroscopy analysis have all shown that the manganese atoms in MoS2 act as a substitute for the molybdenum sites. The microscopic origin of magnetism in Mn-MoS2 is further revealed on the basis of first-principles calculations, which corroborate the experimental results obtained. Our study demonstrates a simple route to creating 2D ferroelectric materials with broad prospects in spintronic devices and next-generation memory components.

Electro-Elastic Modeling of Multi-Step Transitions in Two Elastically Coupled and Sterically Frustrated 1D Spin Crossover Chains

One-dimensional spin crossover (SCO) solids that convert between the low spin (LS) and the high spin (HS) states are widely studied in the literature due to their diverse thermal and optical characteristics which allow obtaining many original behaviors, such as large thermal hysteresis, incomplete spin transitions, as multi-step spin transitions with self-organized states. In the present work, we investigate the thermal behaviors of a system of two elastically coupled 1D mononuclear chains, using the electro-elastic model, by including an elastic frustration in the nearest neighbors (nn) bond length distances of each chain. The chains are made of SCO sites that are coupled elastically through springs with their nn and next-nearest neighbors. The elastic interchain coupling includes diagonal springs, while the nn inter-chain distance is fixed to that of the high spin state. The model is solved using MC simulations, performed on the spin states and the lattice distortions. When we only frustrate the first chain, we found a strong effect on the thermal dependence of the HS fraction of the second chain, which displays an incomplete spin transition with a significantly lowered transition temperature. In the second step, we frustrate both chains by imposing different frustration rates. Here, we demonstrate that for high frustration values, the thermal dependence of the total HS fraction exhibits multi-step spin transitions. The careful examination of the spin state structures in the plateau regions showed the coexistence of special dimerized ferro–antiferro patterns of type LL-HH-LL-HH along the first chain and HH-LL-HH-LL (H=HS and L=LS) along the second one, revealing that the two chains are antiferro-elastically coupled. This type of spatial modulation of the spin state and bond length distances is very attractive because it anticipates the possible existence of periodic structures in 2D lattices, made of alternate 1D SCO strings with HLHLHL structures, coupled in the ferro-like fashion along the interchain direction.