Phase Transitions In Materials Research Articles

Аккумулирование тепловой энергии масла и охлаждающей жидкости дизельного двигателя маневрового тепловоза

Objective: to substantiate the effectiveness of using heat-storing materials to preserve the thermal energy of the oil and coolant of the diesel power plant of a shunting diesel locomotive. To achieve this goal it is necessary: to identify the relevance of the problem of preserving the thermal energy of oil and coolant during the operation of diesel locomotives in conditions of negative ambient temperatures; develop a concept for the use of heat-storing phase transition materials in the oil and water systems of a diesel locomotive; carry out the selection of heat-storing materials based on their physical properties and the operating characteristics of diesel locomotive engine systems; conduct laboratory experimental studies to assess the effectiveness of using a particular heat-storing material. Methods: physical experiment performed in laboratory conditions, which consists of recording the temperature of the working medium (oil and water) and the temperature of the heat-storing material used depending on the cold idle time. Experimental studies make it possible to more accurately select the most preferred materials for accumulating heat from oil and water in diesel locomotive engine systems. Results: an experimental dependence of the temperature of various heat-accumulating materials on the cold idle time was constructed, which makes it possible to justify the use of stearin to accumulate heat from engine oil and cooling system water. Practical importance: the research was carried out as part of the implementation of a grant from Russian Railways JSC for young scientists to conduct scientific research aimed at creating new equipment and technologies for use in railway transport and recommended for use in the locomotive complex. Grant agreement No. 5103675 dated December 26, 2022 “Thermal accumulator for the pre-start preparation system for diesel locomotives in the cold season”

A stable and visualized fatty acid-based phase transition material constructed by solid-phase molecular self-assembly for thermal management.

Fatty acids are excellent thermal management materials for thermal storage, release and preventing thermal runaway. However, the leakage of fatty acids leads to instability and prevents their application in thermal management. Herein, a stable and visualized fatty acid-based phase transition material P-S/PA was constructed through solid-state molecular self-assembly strategy from polydiallyldimethylammonium chloride (PDDA), sodium dodecyl benzene sulfonate (SDBS) and palmitic acid (PA). The electrostatic interaction between PDDA and SDBS and hydrophobic interaction between PA and SDBS can prevent PA leakage during phase transition, achieving stability. After 1000 cycles, the changes in the phase transition enthalpy (ΔH M, ΔH C) were less than 1%. The structural similarity also made P-S/PA phase transition visible, and the transmittance changed significantly from 0% to 68% during phase transition. In addition, P-S/PA can be remolded by hot-pressing without performance changes, showing temperature adjustability on varying the fatty acid carbon chain length. Thus, the stable and visualized P-S/PA fatty acid-based phase transition material constructed by solid-phase molecular self-assembly has promising application in thermal management.

Diffusion-induced stress amplification in phase-transition materials for electrodes of lithium-ion batteries

This work sheds the light on the stress amplification in active material particles of electrodes caused by the localized lithium concentration inhomogeneity due to phase transitions. This is a significant issue usually neglected in the literature, as generally the ideal Fickian diffusion model is used to describe the lithium diffusion, which particularly fails when dealing with phase change materials, resulting in the underestimation of the stress. In turn, this results in the underestimation of the fracture behaviour of the electrode and the battery degradation, ultimately.To overcome these limitations, this work proposes a mechanical-transport model where the lithium transport is modelled according to the non-ideal solution theory with an equivalent diffusion coefficient depending on the potential of the host material vs Li/Li+. The results show that the proposed model correctly describes the concentration distribution within the particle of phase-change materials (graphite is chosen as a case study), in agreement with the existent experimental measurements. The differences with respect to the traditional Fickian diffusion model is substantial as the stress is up to 85% higher with the proposed model and the concentration distribution can capture the inhomogeneity caused by phase transitions.

Phase Transition Control in Molecular Solids via Complementarity of Hydrogen-Bond Strength.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin CoIIcom-pounds were isolated and systematically investigated by modifying the ligand terminal groups (X = S, Se) and substituents (Y = Cl, Br).S-ClandSe-Brundergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX-ligands, accompanied by switchable magnetism. Conversely,S-BrandSe-Clretain stability in ordered and disordered phases, respectively. H-bonds geometric analysis andab initiocalculations reveal that the electronegativity of X and Y affects the strength of NY-ap-H···X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor andvice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective.

MEMS-actuated terahertz metamaterials driven by phase-transition materials

The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO2). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO2, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems.Graphical

Room-Temperature Phase Transition Material with Switchable Second-Order Nonlinear Optical Properties.

Phase transition materials with switchable second-order nonlinear optical (NLO) properties have attracted extensive attention because of their great application potential in photoelectric switches, sensors, and modulators, while metal-free organics with NLO switchability near room temperature remain scarce. Herein, we report a hydrogen-bonded metal-free organic crystal, 2-methylpropan-2-aminium 2,2-dimethylpropanoate (1), exhibiting a room-temperature phase transition and favorable NLO switchability. Through investigations on its thermal anomalies, dielectric properties, and crystal structures, we uncover that 1 holds a near-room-temperature phase transition at 303 K from noncentrosymmetric point group C2v to centrosymmetric one D2h, which is attributed to the order-disorder transformations of both tert-butylamine cations and dimethylpropionic acid anions. Accompanied by symmetry change during the phase transition, 1 exhibits reversible and repeatable NLO "on-off" switchability with a desirable switching contrast ratio of ca. 19 between high and low NLO states. This discovery demonstrates a metal-free organic crystal with NLO switching behavior near room temperature, serving as a promising candidate in smart and ecofriendly photoelectric functional materials and devices.

Tunable polarization-independent and angle-insensitive ultra-broadband terahertz absorber with vanadium dioxide

In this paper, a tunable ultra-broadband terahertz metamaterial absorber is proposed based on the phase transition material of vanadium dioxide (VO2). The absorber cell consists of a petal-like monolayer vanadium dioxide, a dielectric layer, and a metal layer. The terahertz absorption bandwidth of more than 90% absorptance reaches 4.2 THz, which covers from 1.99 to 6.19 THz, and a relative bandwidth attains to 102.7%. By changing the conductivity of VO2, the absorbance of this structure can be dynamically adjusted from 2.4% to 98.96%. The physical mechanism of the perfect absorption in this paper is investigated by the impedance matching theory and electric field distributions. The results show that the strong coupling effect in the petal-like structure contributes to the broadening of the absorption spectrum, and the absorber is polarization-insensitive and wide-angle incidence-insensitive due to the symmetry of the cell structure. The metamaterial absorber designed in this paper is expected to have a wide range of applications in the fields of terahertz imaging, stealth, sensing and detection.

Large relative cooling power in van der Waals room-temperature ferromagnet Fe5GeTe2

Due to the unique structures, van der Waals (vdW) materials have advantages over traditional magnetothermal materials in manipulating magnetothermal properties through structural modification and in cooling applications in nanodevices. Here, we study the magnetothermal properties of vdW ferromagnet Fe5GeTe2 with Curie temperature around room temperature. The results show that Fe5GeTe2 is a second-order magnetic phase transition material, and its in-plane and out-of-plane values of relative cooling power are large up, respectively, to 299.3 and 269.2 J/kg for a field change of 5 T. Compared to other vdW materials reported, Fe5GeTe2 has the greatest potential for room-temperature magnetic cooling applications.

Neuromorphic one-shot learning utilizing a phase-transition material

Design of hardware based on biological principles of neuronal computation and plasticity in the brain is a leading approach to realizing energy- and sample-efficient AI and learning machines. An important factor in selection of the hardware building blocks is the identification of candidate materials with physical properties suitable to emulate the large dynamic ranges and varied timescales of neuronal signaling. Previous work has shown that the all-or-none spiking behavior of neurons can be mimicked by threshold switches utilizing material phase transitions. Here, we demonstrate that devices based on a prototypical metal-insulator-transition material, vanadium dioxide (VO2), can be dynamically controlled to access a continuum of intermediate resistance states. Furthermore, the timescale of their intrinsic relaxation can be configured to match a range of biologically relevant timescales from milliseconds to seconds. We exploit these device properties to emulate three aspects of neuronal analog computation: fast (~1 ms) spiking in a neuronal soma compartment, slow (~100 ms) spiking in a dendritic compartment, and ultraslow (~1 s) biochemical signaling involved in temporal credit assignment for a recently discovered biological mechanism of one-shot learning. Simulations show that an artificial neural network using properties of VO2 devices to control an agent navigating a spatial environment can learn an efficient path to a reward in up to fourfold fewer trials than standard methods. The phase relaxations described in our study may be engineered in a variety of materials and can be controlled by thermal, electrical, or optical stimuli, suggesting further opportunities to emulate biological learning in neuromorphic hardware.

Intermolecular Forces Regulating the Phase-Transition Temperatures in Organic-Inorganic Hybrid Materials.

Organic-inorganic hybrid phase-transition materials have attracted widespread attention in energy storage and sensor applications due to their structural adaptability and facile synthesis. However, increasing the phase-transition temperature (Tc) effectively remains a formidable challenge. In this study, we employed a strategy to regulate intermolecular interactions (different types of hydrogen bonds and other weak interactions), utilizing bismuth chloride as an inorganic framework and azetidine, 3,3-difluoro azetidine, and 3-carboxyl azetidine as organic components to synthesize three compounds with different Tc values: [C3H8N]2BiCl5 (1, 234 K), [C3H6NF2]3BiCl6 (2, 256 K), and [C4H8O2N]3BiCl6 (3, 350 K). 1 is a one-dimensional chain structure and 2 and 3 are zero-dimensional structures. Analysis of the crystal structure and the Hirshfeld surface and 2D fingerprints further suggests that the intermolecular forces are efficiently modulated. These findings emphasize the efficacy of our strategy in enhancing Tc and may facilitate further research in this area.

A Numerical Study of the Effect of Water Speed on the Melting Process of Phase Change Materials Inside a Vertical Cylindrical Container

The present work offers a thorough analysis of the impact of water velocity on phase change material (PCM) melting in a vertical cylindrical container. A detailed quantitative analysis uses sophisticated numerical techniques, namely the ANSYS/FLUENT 16 program, to clarify the complex relationship between enthalpy and porosity during the melting process. The experimental focus is on phase transition materials based on paraffin wax, particularly Rubitherm RT42. This study’s primary goal is to evaluate the effects of different water velocities (that is, at velocities of 0.01 m/s, 0.1 m/s, and 1 m/s) on the PCM’s melting behavior at a constant temperature of 333 K. This work intends to make a substantial contribution to the development of thermal energy storage systems by investigating new perspectives on PCM behavior under various flow circumstances. The study’s key findings highlight the possible ramifications for improving PCM-based thermal energy storage devices by revealing significant differences in melting rates and behavior that correlate to changes in water velocities. Future research is recommended to explore the impact of temperature variations, container geometries, and experimental validation to improve the accuracy and practicality of the results and to advance the creation of sustainable and effective energy storage solutions.

Evaluation of various phase-transition materials for steep switching super-low power application in the latest technology node

Recently, a phase-transition field effect transistor (phase-FET) integrated with a phase-transition material (PTM) is attracting attention as a steep switching device, and attempts to solve the power consumption limitation of conventional CMOS using various PTMs are continuing. In order to utilize the phase-FET, it is essential to design an appropriate device and circuit characteristics by carefully considering the close correlation between the baseline-FET and the PTM and the hysteresis characteristics caused by the phase-transition. In this work, by integrating various PTMs according to the baseline FETs in various technology nodes, the logic and SRAM characteristics implemented the phase-FET were investigated, and the appropriate PTM and the electrical characteristic target required for the PTM were presented through systematic analysis. As a result, it was confirmed that single crystalline vanadium di-oxide (SC VO2) has characteristics suitable for constructing phase-FETs compared to other candidate PTMs in 32 nm planar FET, 7 nm Fin-FET, and 3 nm gate-all-around FET technology nodes. As a result of benchmarking with conventional-FET at each technology node, in the case of logic, the speed is 26.15% (32 nm), 20.26% (7 nm), and 20.05% (3 nm), and in the case of memory, standby power, read stability and write time are improved.

Numerical investigation of an amalgamation of two phase change materials thermal energy storage system

In the last three decades, many researchers have published their findings on the storage of thermal energy using various phase transition materials (both organic and non-organic). One of their goals was to have a higher heat storage capacity with a shorter heat charging cycle for thermal energy storage. This study looked into a floating capsule thermal energy storage system (TESS). A number of spherical capsules filled with beeswax were placed in a paraffin-filled cylindrical shell. With heat transfer fluid flowing through three hexagonal tubes arranged at 120° inside the TESS core, the two phase change materials (beeswax with a thermal conductivity of 0.25 W/mK and paraffin with a thermal conductivity of 0.23 W/mK) were charged and discharged. For the proposed TESS, a mathematical model was created and utilised to forecast thermal energy storage capacity and charging/discharge times for various configurations. In TESS, a 70–30% mixture of the two PCMs results in a 21.5 percent increase in heat storage capacity when beeswax alone is used, and an 8.4 percent decrease in storage capacity when paraffin alone is used. For a heat storage capacity of 7300 kJ, the model estimates charging and discharging times of around 2.6 and 3.2 hours, respectively.

Novel polyurethane foam with low released heat for application in bone binder

AbstractBecause of the significant advantages of bone adhesives compared with traditional mechanical fixation, many scholars have studied polyurethane bone adhesives. However, polyurethane will release a lot of heat in the reaction process, producing high temperature. The high temperature does not only easily cause a human discomfort but also will destroy the tissue structure of human. In this paper, a new polyurethane composite based on phase transition materials and hydroxyapatite is prepared to reduce released heat for application in bone binder. The mechanical properties, adhesive strength, and released heat‐induced temperature of polyurethane composite are investigated in detail. It exhibits good viscoelastic performance with a large elastic deformation (>30%) and good adhesive strength (>0.2 MPa). Furthermore, the released heat of polyurethane composite is effectively reduced, in which the temperature drastically decreases from 110.4 to 41.8°C. The work does not only confirm formation of high‐performance bone binder but also provides a new method to reduce released heat of polyurethane for various applications.

Nanoelectrical monitoring the nonvolatile behavior of VO2 under multi-field stimulate by conductive atomic force microscopy

The ability to control the metal–insulator phase transition is crucial for future neuromorphic and memristive technologies. The key goal of this implementation is to understand and control the nanoscale mechanisms that support these two fundamental switching modalities (volatile and non-volatile states). Here, by adjusting the temperature (60 °C) close to the metal–insulator transition temperature, external application of low voltage (1 V) and laser excitation (18.6 mw · cm−2) can complete the metal–insulator transition of vanadium dioxide (VO2). The nonvolatile behavior of the VO2 devices was nanoelectrically monitored using conductive atomic force microscopy (C-AFM). Using this technique, we were able to reversibly transform the local switching response from volatile to nonvolatile, providing a unique approach for nanoelectrical monitoring in phase transition materials.

Computational Fluid Dynamic Analysis of Solar Dryer Equipped with Different Phase Change Materials

A phase change material (PCM) is an organic (or inorganic) chemical that may store and release thermal energy in latent form as it changes physical states. This investigation aims to see how phase transition materials influence the thermal efficiency of the solar dryer. For the performance analysis, three PCMs were used: paraffin wax, lauric acid, and palmitic acid. As drying material, 5 mm thick potato slices were employed. According to the computational results, the total input thermal energy for the dryer for paraffin wax, lauric acid, and palmitic acid was about 17.36 MJ, 18.46 MJ, and 17.76 MJ, respectively, for 2 kg drying mass. When paraffin wax, lauric acid, and palmitic acid were utilized, the overall efficiency of the dryer increased by about 87%, 40.2%, and 12.4%, respectively, compared to the conventional dryer. By comparing the results of simulations and predictions, it is concluded that paraffin wax is the best-performing PCM for solar dryers as the energy storage material.

Novel hybrid-CMOS inverter utilizing phase transition material for enhancing digital logic performance at lower operating voltages

This research paper introduces a novel design for a hybrid-CMOS inverter using vanadium dioxide (VO2), a phase transition material. The proposed inverter exhibits a remarkably steep transition for falling logic at the output(1–0). By leveraging the insulating to metallic current density (IC-IMT) of VO2, the depth and gain of this transition can be finely tuned. Notably, a higher IC-IMT value yields a greater gain in the transition slope. In comparison to a traditional CMOS inverter, the designed inverter demonstrates several advantages. It achieves higher values of lower noise margin (NML) and significantly reduces static power dissipation by 97.7%. These promising outcomes present an exciting opportunity for designing inverters at lower drain voltages, especially in devices operating at lower technology nodes. Furthermore, the hybrid-CMOS inverter is designed to excel in the sub-threshold region of operation, resulting in elevated values of lower noise margin and reduced leakage current values.

Tuning ferroelectric phase transition temperature by enantiomer fraction

Tuning phase transition temperature is one of the central issues in phase transition materials. Herein, we report a case study of using enantiomer fraction engineering as a promising strategy to tune the Curie temperature (TC) and related properties of ferroelectrics. A series of metal-halide perovskite ferroelectrics (S−3AMP)x(R−3AMP)1−xPbBr4 was synthesized where 3AMP is the 3-(aminomethyl)piperidine divalent cation and enantiomer fraction x varies between 0 and 1 (0 and 1 = enantiomers; 0.5 = racemate). With the change of the enantiomer fraction, the TC, second-harmonic generation intensity, degree of circular polarization of photoluminescence, and photoluminescence intensity of the materials have been tuned. Particularly, when x = 0.70 − 1, a continuously linear tuning of the TC is achieved, showing a tunable temperature range of about 73 K. This strategy provides an effective means and insights for regulating the phase transition temperature and chiroptical properties of functional materials.

Preparation and Properties of Graphene/Novel Degradable Plastics Hybrid Low Enthalpy of Phase Transition Materials

Graphene (GNs) were chosen to modify hybrid and novel degradable plastics PTLA/polymethyl methacrylate (PMMA). The low enthalpy of melting phase transformation (MEPT) materials (PTLA/PMMA)/GNs were prepared by adding the GNs at different mass fraction(1%, 2%, 3%, 4%) into PTLA/PMMA, and the properties of the hybrid phase change materials were characterized. The results indicated that the MEPT of PTLA/PMMA materials can be significantly reduced with the addition of GNs. The addition of 3% (mass) GNs made the MEPT of PTLA/PMMA material decreased by more than 50%. With the increase of GNs mass fraction, the MEPT hardly changed; Fourier transformed infrared (FT-IR) spectra showed that the interaction between GNs and PTLA/PMMA was physical; Scanning electron microscope (SEM) images showed that the components of GNs and PTLA/PMMA were mixed evenly without phase separation; The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) cycle performance tests showed that the decomposition temperature of the (PTLA/PMMA)/GNs material was up to 280 °C, and the properties could remain stable during the circulation process. The addition of GNs could effectively reduce the MEPT of the (PTLA/PMMA)/GNs material, increase the heat transfer efficiency, and have good thermal reliability.

Reversible Elastomer–Fluid Transitions for Metamorphosic Robots

AbstractEndowing robots with reversible phase transition ability, especially between elastomer and fluid states, can significantly broaden their functionality and applicability. Limited attempts have been made to realize the reversible elastomer–fluid transition. Existing phase transition materials in robotics have over‐hard (≈4 GPa) or over‐soft (≈4 kPa) stiffness in the solid states, which should be further investigated to perform more compliant motions. To address these challenges, a reversible elastomer–fluid transition mechanism enabled by magnetically induced hot melt materials (MIMMs) is presented. The transition principle is explained and material characterizations are conducted. MIMMs‐based metamorphosic robots endow self‐metamorphosing abilities, such as self‐healing, spatial reshaping, self‐division/assembly, and additive manufacturability. When interacting with external environments, MIMMs‐based robots can perform further multifunctional abilities, such as collaborations for structure repairs, swimming by symbiosis with external objects, flowing through a narrow terrain by transiting to fluid, and working with elastomeric structures for stiffness‐variable fluid soft actuators. The proposed elastomer–fluid transitions open a new path for robots to generate more flexible and metamorphosic motions, thereby addressing the cross‐phase transformation challenges that soft robots face.