Induced Phase Transition Research Articles

Realizing high-resistivity and low-loss Fe–Si–Al based soft magnetic powder cores through interfacial chemistry regulation

As a symbolic ceramic oxide, SiO2 is one of the most important insulating layers of soft magnetic powder cores (SMPCs). Thus, the reaction of SiO2 with Fe–Si–Al based SMPC substrates during annealing, the induced phase transition of the core-shell structure, and the influence of the latter on the magnetic characteristics of SMPCs are worth investigating. In this study, Fe–Si–Al based SMPCs were successfully synthesised using fluidised-bed chemical vapour deposition (FB-CVD) at various times, combined with an electric pressure-assisted sintering method and high-temperature annealing. The evolution of the insulating layers with different thicknesses was investigated. With increasing thickness, the insulating layers (shell) gradually transformed into Al2O3 and the Fe–Si–Al substrate (core) to Fe3Si. The newly formed Al2O3 and Fe3Si increased the coercivity and saturation magnetisation of the SMPCs, while the hysteresis loss increased with thicker insulating layers. The generated Al2O3 improved the integrity of the insulating layers, preventing possible point contact between particles, and significantly reduced the Eddy current losses. The SMPCs with the thickest insulating layers (7#) exhibited superior magnetic properties (Ms = 129.3 emu/g, resistivity = 2.51 mΩ cm, total loss = 593.1 kW/m3 at 10 mT and 100 kHz; 18.0% reduction from the maximum). Thus, a precise method of adjusting the magnetic behaviour of Fe–Si–Al based SMPCs was developed through the novel approach of building SMPCs with inorganic ceramic insulating layers, enabling a comprehensive understanding of the relationship between the thickness of insulating layers and magnetic properties, which is of significance for industrial production.

Phase engineering in nanocrystalline high-entropy alloy composites to achieve strength-plasticity synergy

In this work, the strength-plasticity synergy of Al/CoCrFeNi nanocrystalline high-entropy alloy composite (nc-HEAC) prepared by laser-inert gas condensation is achieved via nanoscale diffusion induced phase transition (DIPT) process. The yield strength and elongation of the 16%-Al/CoCrFeNi nc-HEAC annealed at 900 °C were 1338 MPa and 12.1%, showing the combination of outstanding strength and considerable ductility. The synergy of multiple strengthening mechanisms were revealed. Driving the phase transition of nanocrystalline dual-phase composites by thermal diffusion establishes a novel phase engineering design strategy for high-performance alloys.

Morphology control of volatile resistive switching in La0.67Sr0.33MnO3 thin films on LaAlO3 (001)

The development of in-memory computing hardware components based on different types of resistive materials is an active research area. These materials usually exhibit analog memory states originating from a wide range of physical mechanisms and offer rich prospects for their integration in artificial neural networks. The resistive states are classified as either non-volatile or volatile, and switching occurs when the material properties are triggered by an external stimulus such as temperature, current, voltage, or electric field. The non-volatile resistance state change is typically achieved by the switching layer’s local redox reaction that involves both electronic and ionic movement. In contrast, a volatile change in the resistance state arises due to the transition of the switching layer from an insulator to a metal. Here, we demonstrate volatile resistive switching in twinned LaAlO3 onto which strained thin films of La0.67Sr0.33MnO3 (LSMO) are deposited. An electric current induces phase transition that triggers resistive switching, close to the competing phase transition temperature in LSMO, enabled by the strong correlation between the electronic and magnetic ground states, intrinsic to such materials. This phase transition, characterized by an abrupt resistance change, is typical of a metallic to insulating behavior, due to Joule heating, and manifested as a sharp increase in the voltage with accompanying hysteresis. Our results show that such Joule heating-induced hysteretic resistive switching exhibits different profiles that depend on the substrate texture along the current path, providing an interesting direction toward new multifunctional in-memory computing devices.

Optical properties and mechanical induced phase transition of CsPb2Br5 and CsPbBr3 nanocrystals

The Cs-Pb-Br system possesses excellent optical properties and unique phase transition characteristics due to soft lattice structures. Herein, a simple and green synthetic method based on self-assembly in Dimethyl formamide (DMF) is proposed to prepare CsPb2Br5 nanocrystals (NCs) with typical tetragonal structure, which exhibit orange emission and small size around 3.87 nm. Interestingly, the phase transition from CsPb2Br5 to CsPbBr3 occurs easily in DMF through mechanical induction, while the metastable mixed-phase structural CsPbBr3 NCs with an average size of about 5 nm appear and show bright yellow emission. Afterwards, in combination with the supersaturation crystallization method, stable cubic CsPbBr3 NCs with 13 nm size are obtained and display the effective green emission. The synthesized CsPb2Br5 and steady-state CsPbBr3 NCs exhibit good optical stability in solution, while the metastable CsPbBr3 NCs undergo a change in emission from yellow to green with increasing time.

Thermally Induced Phase Transition of Polybutene-1 from Form I′ to Form II through Melt Recrystallization: Crucial Role of Chain Entanglement

Thermally Induced Phase Transition of Polybutene-1 from Form I′ to Form II through Melt Recrystallization: Crucial Role of Chain Entanglement

Soft Actuators Based on Spin‐Crossover Particles Embedded in Thermoplastic Polyurethane

Molecular spin‐crossover (SCO) complexes are phase‐change materials that develop large spontaneous strains across the thermally induced phase transition, which can be advantageously used in designing soft actuators. Herein, a bilayer bending cantilever, made of thermoplastic polyurethane (TPU) with embedded [Fe(NH2trz)3](SO4) SCO particles (25 wt%), is presented. The proposed actuator is fabricated by blade casting an SCO@TPU layer on a conducting Ag@TPU film to convert electrothermal input into mechanical response. Experiments are conducted to characterize the curvature of bilayer beams, which is then further analyzed using the Euler–Bernoulli beam theory. The beam curvature change, free transformation strain, and effective work density associated with the SCO are 0.11 mm−1, 1.6%, and 1.25 mJ cm−3, respectively. Further, the open‐ and closed‐loop response of the actuator is investigated using a custom‐built setup. The open‐loop identification suggests that the actuator gain increases monotonously when the control current increases. This natural adaptive character can explain the drastically diminished response time in closed‐loop proportional–integral–derivative control experiments (2–3 s). Finally, tracking experiments are carried out to evaluate the robustness of the actuator with and without payloads. The results for 30 240 endurance cycles reveal a mean positioning error of 0.8%.

Nonvolatile Multilevel Switching of Silicon Photonic Devices with In2O3/GST Segmented Structures

AbstractReconfigurable silicon photonic devices are widely used in numerous emerging fields such as optical interconnects, photonic neural networks, quantum computing, and microwave photonics. Currently, phase change materials (PCMs) have been extensively investigated as promising candidates for building switching units due to their strong refractive index modulation. Here, nonvolatile multilevel switching of silicon photonic devices with Ge2Sb2Te5 (GST) is demonstrated with In2O3 transparent microheaters that are compatible with diverse material platforms. With GST integrated on the silicon photonic waveguides and Mach‐Zehnder interferometers (MZIs), repeatable and reversible multilevel modulation of GST is achieved by electro‐thermally induced phase transitions. Particularly, the segmented switching unit of In2O3 and GST is proposed and demonstrated to be capable of producing about one order of magnitude larger temperature gradient than that of the nonsegmented unit, resulting in up to 64 distinguishable switching levels of 6‐bit precision, and fine‐tuning of the switching voltage pulses is promising to push the precision even further, to 7‐bit, or 128 distinguishable switching levels. The capability of precise multilevel phase‐change modulation is crucial to further facilitate the development of nonvolatile reconfigurable switches and variable attenuation devices as building blocks in large‐scale programmable optoelectronic systems.

Thermally Induced Phase Transition of Cubic Structure II Hydrate: Crystal Structures of Tetrahydropyran–CO2 Binary Hydrate

We report a thermally induced phase transition of cubic structure II hydrates of tetrahydropyran (THP) and CO2 below about 140 K. The phase transition was characterized by powder X-ray diffraction measurements at variable temperatures. A dynamical ordering of the CO2 guests in small pentagonal dodecahedral 512 host water cages, not previously observed in the simple CO2 hydrate, occurs simultaneously with the symmetry lowering transition from a cubic structure II (space group Fd-3m with cell dimensions a = 17.3202(7) Å at 153 K) to a tetragonal (space group I41/amd with cell dimensions a = 17.484(4) Å and c = 12.145(1) Å at 138 K) unit cell. The effect of guest molecules on the phase transition at low temperatures is discussed, which demonstrates that the clathrate hydrate structures and thermodynamic properties can be modified by adjusting the size and chemical structure of larger and smaller guest molecules.

120 MeV swift Au9+ ion induced phase transition in ZrO2: monoclinic to tetragonal and cubic to tetragonal structure

This study reports the effect of 120 MeV swift Au9+ ion irradiation on the structures of monoclinic, tetragonal and cubic ZrO2, probed through x-ray diffraction (XRD) and Raman spectroscopy. Three phases of ZrO2 were prepared using the solution combustion method. The tetragonal and cubic phases of ZrO2 were stabilized at room temperature by adding 6% and 10% of yttrium ions, respectively. Both the XRD and Raman results confirm the partial phase transition from monoclinic to tetragonal, which was approximately 74%. Tetragonal ZrO2 is stable under 120 MeV Au9+ ion irradiation. Interestingly, a phase transition from cubic to tetragonal ZrO2 was observed under 120 MeV Au9+ ion irradiation. The roles of transient temperature, defects and strain in the lattice induced by swift heavy ions are discussed. This study reveals the structural stability of different phases of ZrO2 under swift heavy ion irradiation and should be helpful in choosing potential hosts for various applications such as inert fuel matrix inside the core of nuclear reactors, oxygen sensors and accelerators, and radiation shielding.

Enhancing the toughness of nano-composite coating for light alloys by the plastic phase transformation of zirconia

Toughness of ceramic coatings is essential for engineering deploys of light alloys, especially for the scenarios tackling with corrosion and wear. This work reports a toughened ZrO2/MgO coating on Mg alloy enabled by stress-induced martensite transformation from tetragonal zirconia (t-ZrO2) to monoclinic zirconia (m-ZrO2), which is achieved by the plasma electrolytic oxidation (PEO) process. Observations reveal that the interfaces between ZrO2 and MgO grains are essential in inducing phase transition during the toughening process. Interestingly, semi-coherent interfaces were found between t-ZrO2 and MgO, and the mismatched atoms at the interface cause local lattice distortions. These lattice distortions provide an appropriate dislocation density (2.2 × 105 /m2–4.1 × 105 /m2), which not only ensures the stability of the interface but also provides a stress transfer channel to induce martensite transformation of ZrO2. The plastic phase transformation is accompanied with volume expansion of ZrO2 grains, thus a compressive stress field is generated to resist the crack propagation with an enhancement of the plasticity of the composite ceramics. As a result, the toughness of the enhanced coating is about 1.15 times higher than that of the traditional PEO coating. This work provides an alternative strategy for designing toughened ceramic coatings for light alloys.

Tuning magnetic anisotropy in SrRuO3 thin film by Ru vacancies induced phase transition

Effective control of magnetic anisotropy, including perpendicular magnetic anisotropy (PMA) and lateral magnetic anisotropy, is important for the design of low-power and high-density spintronic devices. However, the rarity of oxide materials with PMA and stringent conditions required to control magnetic anisotropy have prevented its large-scale application. Here, we demonstrate that the magnetic anisotropy of SrRuO3 films can be specified on-demand by adjusting the content of Ru vacancies to control the structure of the films. With the increase in Ru vacancies, the structure of SrRuO3 changes from orthorhombic to tetragonal. The field angle dependence of the Hall resistance confirmed that the uniaxial magnetic easy axis of SrRuO3 thin films continuously rotates in the (100)pc crystallographic plane, which is identical to the continuous phase transition. Our results not only provide a way to continuously tune the physical properties of epitaxial oxide films by continuously changing the composition but also help to provide guidance for the on-demand design of spintronic devices.

Highly efficient p-i-n perovskite solar cells that endure temperature variations.

Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. We stabilized the perovskite black phase and improved solar cell performance using the ordered dipolar structure of β-poly(1,1-difluoroethylene) to control perovskite film crystallization and energy alignment. We demonstrated p-i-n perovskite solar cells with a record power conversion efficiency of 24.6% over 18 square millimeters and 23.1% over 1 square centimeter, which retained 96 and 88% of the efficiency after 1000 hours of 1-sun maximum power point tracking at 25° and 75°C, respectively. Devices under rapid thermal cycling between -60° and +80°C showed no sign of fatigue, demonstrating the impact of the ordered dipolar structure on the operational stability of perovskite solar cells.

Quantum order-by-disorder induced phase transition in Rydberg ladders with staggered detuning

^{87} Rb87Rb atoms are known to have long-lived Rydberg excited states with controllable excitation amplitude (detuning) and strong repulsive van der Waals interaction V_{{r} {r'}}Vrr′ between excited atoms at sites {r}r and {r'}r′. Here we study such atoms in a two-leg ladder geometry in the presence of both staggered and uniform detuning with amplitudes \DeltaΔ and \lambdaλ respectively. We show that when V_{{r r'}} \gg(\ll) \Delta, \lambdaVrr′≫(≪)Δ,λ for |{r}-{r'}|=1(>1)|r−r′|=1(>1), these ladders host a plateau for a wide range of \lambda/\Deltaλ/Δ where the ground states are selected by a quantum order-by-disorder mechanism from a macroscopically degenerate manifold of Fock states with fixed Rydberg excitation density 1/41/4. Our study further unravels the presence of an emergent Ising transition stabilized via the order-by-disorder mechanism inside the plateau. We identify the competing terms responsible for the transition and estimate a critical detuning \lambda_c/\Delta=1/3λc/Δ=1/3 which agrees well with exact-diagonalization based numerical studies. We also study the fate of this transition for a realistic interaction potential V_{{r} {r'}} = V_0 /|{r}-{r'}|^6Vrr′=V0/|r−r′|6, demonstrate that it survives for a wide range of V_0V0, and provide analytic estimate of \lambda_cλc as a function of V_0V0. This allows for the possibility of a direct verification of this transition in standard experiments which we discuss.

Phase Transformation of VO2/rGO Composites as High‐Voltage Cathodes in Zinc‐Ion Batteries

AbstractAqueous zinc‐ion batteries (ZIBs) are becoming widely concerned candidates as stationary and safe energy storage technology. Vanadium oxides display promising role as cathodes for ZIBs owing to their inherent merits in structures and multiple valence states. However, their unsatisfactory electrical conductivity and narrow voltage window hinder the practical application. Moreover, the charge storage mechanism at the high voltage is unclear. Herein, we synthesized VO2/rGO composites with high electrical conductivity and demonstrated an electrochemically induced phase transition from tunneled VO2/rGO to Zn3(OH)2V2O7 ⋅ 2H2O/rGO with a laminated structure and an enhanced interlayer spacing during the first charge to 1.6 V, which shows preferable Zn2+ storage capacity. Concretely, the electrochemical window of as‐assembled ZIB expands to 1.6 V with a specific capacity of 329.9 mAh g−1 at 0.1 A g−1, exhibiting wider window compared with the ZIBs based vanadium oxide reported previously. Simultaneously, a long stable lifetime of 84 % capacity retention over 1,000 cycles can be recorded. Our work opens a new idea of design strategy to develop high‐voltage ZIBs.

Supramolecular design of CO2-responsive lipid nanomaterials

HypothesisStimuli-responsive materials can innovate in various fields, including food and pharmaceutical sciences. Their response to a specific stimulus can be utilized to release loaded bioactive molecules or sense their presence. The biocompatibility and abundance of CO2 in the environment make it an exciting stimulus for such applications. We hypothesize the formation of CO2-responsive self-assemblies of oleyl-amidine in water. Their integration into glycerol-monooleate-based (GMO) dispersions is further thought to form CO2-switchable liquid crystalline nanoparticles. The switch from an non-charged acetamidine surfactant to its cationic amidinium form triggers curvature changes that ultimately induces phase transitions. ExperimentsThe CO2-switchable lipid (E)-N,N-dimethyl-N-((Z)-octadec-9-en1-yl)acetimidamide (OAm) is synthesized and formulated into emulsions and dispersed liquid crystals with GMO. The supramolecular structure and its response to CO2 are characterized using small angle X-ray scattering, dynamic light scattering, ζ-potential measurements and cryogenic transmission electron microscopy. FindingsDepending on the composition, OAm is discovered to self-assemble into a variety of CO2-responsive lyotropic liquid crystalline structures that can be dispersed in excess water. CO2-triggered colloidal transformations from unstructured OAm-in-water emulsions to direct micelles; dispersed inverse hexagonal phase to direct rod-like micelles, and sponge phase to vesicles are discovered. These structural changes are driven by the reaction of OAm’s amidine headgroup with CO2. The results provide a fundamental understanding of CO2-triggered functional nanomaterials and may guide their future design into delivery platforms and biosensors.

A Biomimetic Bilayer Hydrogel Actuator Based on Thermoresponsive Gelatin Methacryloyl-Poly(N-isopropylacrylamide) Hydrogel with Three-Dimensional Printability.

Development of hydrogel-based actuators with programmable deformation is an important topic that arouses much attention in fundamental and applied research. Most of these actuators are nonbiodegradable or work under nonphysiological conditions. Herein, a temperature-responsive and biodegradable gelatin methacryloyl (GelMA)-poly(N-isopropylacrylamide) hydrogel (i.e., GN hydrogel) network was explored as the active layer of a bilayer actuator. Small-angle X-ray scattering (SAXS) revealed that the GN hydrogel formed a mesoglobular structure (∼230 Å) upon a thermally induced phase transition. Rheological data supported that the GN hydrogel possessed 3D printability and tunable mechanical properties. A bilayer hydrogel actuator composed of active GN and passive GelMA layers was optimized by varying the layer thickness and compositions to achieve large, reproducible, and anisotropic bending with a curvature of ∼5.5 cm-1. Different patterns of the active layer were designed for actuation in programmable control. The 3D printed GN hydrogel constructs showed significant volume reduction (∼25-60% depending on construct design) at 37 °C with the resolution enhanced by the thermo-triggered actuation, while they were able to fully reswell at room temperature. A more intricate 3D printed butterfly actuator demonstrated the ability to mimic the wing movement through thermoresponsiveness. Furthermore, myoblasts laden in the GN hydrogel exhibited significant proliferation of ∼376% in 14 days. This study provides a new fabrication approach for developing biomimetic devices, artificial muscles, and soft robotics for biomedical applications.

Resistive switching polarity reversal due to ferroelectrically induced phase transition at BiFeO3/Ca0.96Ce0.04MnO3 heterostructures

Ferroelectric resistive switching (RS) devices with functional oxide electrodes allow controlled emergent phenomena at an interface. Here, we demonstrate RS polarity reversal due to ferroelectrically induced phase transition at a doped charge transfer insulator interface. For BiFeO3/Ca0.96Ce0.04MnO3 bilayers grown on a NdAlO3 substrate, by applying voltages to a Ca0.96Ce0.04MnO3 bottom electrode, the resistance changes from a high resistance state (HRS) to a low resistance state (LRS) during a positive voltage cycle (0 → 3 → 0 V), and from a LRS to a HRS during a negative voltage cycle (0 → −3 → 0 V). The RS polarity is completely opposite the expected RS behavior in ferroelectric heterostructures induced by polarization reversal. It is proposed that the unique resistance switching polarity is attributed to the band-filling controlled metal-insulator transition in a Ca0.96Ce0.04MnO3 film, triggered by ferroelectric based electrostatic doping. The results address the importance of ferroelectric field effect on the electronic properties of the interfacial system in ferroelectric/complex oxide-based resistive memory devices.

Fluid–Structure Interaction of a thin cylindrical shell filled with a non-Newtonian fluid

This paper presents the results of an extensive experimental campaign on the dynamic interactions between an elastic structure and a non-Newtonian fluid. The structure consists of a thin circular cylindrical shell, with the bottom end clamped to a shaking table, and the top end carrying a heavy mass. The fluid is a mixture of water and cornstarch, also known as oobleck. The system dynamics has been analyzed in the presence of different fluid levels (i.e., empty, partially, and full-filled). The experimental modal analysis has been carried out to identify the modal properties of the system. High energy tests have been performed by means of a seismic excitation consisting in a stepped sine sweep, spanning the forcing frequency within the neighborhoods where strong resonance phenomena take place. Different excitation amplitudes have been considered in order to induce phase transitions in the fluid, and the onset of complex dynamics has been detected using Fourier spectra and bifurcation diagrams of the Poincaré maps: when the fluid–solid​ transition occurs, the entangled non-Newtonian fluid rheology results in a complex dynamic scenario where period-doubling cascades, quasiperiodic and chaotic responses can be observed.

Nanostructure-dependent nanobubble drag reduction on NiTi self-adaption surface

Under the inspiration of visualized nanobubbles associated with rugged interface, molecular simulations are performed to study thermally induced phase transition in NiTi shape-memory alloys. The perfect reversibility between the cubic austenite B2 and monoclinic martensitic B19′ phases showed two types of morphological structures in the nanoscale. The nanostructures were established as the wall of the nanochannel, which was used to predict the nanobubble flow behavior in the ternary system. Results indicated that the interface with low-temperature B19′ exhibited attractiveness to trap the nanobubble, resulting in low drag coefficient. Conversely, the interface with high-temperature B2 repulsed the nanobubbles as the bulk one, resulting in high drag coefficient. This study provides foresight to invest in shape memories for nanostructure temperature response, which helps realize nanobubble drag reduction.

Measuring T1 relaxation in paramagnetic solids with solid-state NMR: a case study on the milling induced phase transition in Li6CoO4.

Solid-state NMR has been a vital tool for the study of structural evolution of cathodes in lithium-ion and sodium-ion batteries. However, the differentiation of relaxation parameters for certain sites is difficult owing to limited spectral resolution associated with strong anisotropic hyperfine interaction. Here we propose a novel IR-pjMATPASS method that can measure T1 relaxation with site-specific resolution for paramagnetic solids. We apply this method to the characterization of ball-milling induced order-disorder phase transition in Li6CoO4 as a case study. The quasi-quantitate 7Li NMR enables the synthetic optimization of high energy ball-milling conditions to harvest a disordered cubic phase through site-specific 7Li T1 measurements. The example study shown here provides a quantitative strategy for NMR studies of paramagnetic solids.