Reverse Phase Transition Research Articles

Physical mechanism for nanocrystalline NiTi alloy with ultrasmall-sized grains exhibiting one-way shape memory effect without temperature-induced phase transformation

In the present work, a novel finding is that nanocrystalline NiTi alloy with ultrasmall-sized grains (where the diameter of grains is less than or equal to 10 nm) presents one-way shape memory effect (OWSME) without temperature-induced phase transformation, where the involved physical mechanism is revealed by combining experiments with molecular dynamics simulation (MD). The results show that fraction of grain boundaries (GBs) is so much that temperature-induced martensitic transformation is suppressed, but it leads to a certain unrecoverable strain. The following loading results in increase of strain and decrease of Gibbs free energy, which leads to stress-induced martensitic transition. After unloading, Gibbs free energy is increased by the release of elastic strain, which leads to partial reverse martensitic transition. Consequently, OWSME in nanocrystalline NiTi alloy with ultrasmall-sized grains is aroused by retained stress-induced martensitic transition followed by its reverse phase transition rather than temperature-induced one followed by its reverse phase transition.

Pressure/temperature-assisted crystallographic engineering–A strategy for developing the infrared phosphors

Light-emitting diodes utilizing the near-infrared (NIR), harnessed through the doping of Cr ion with structural engineering to tune the luminescent properties, provide a compelling avenue for cutting-edge high-tech industries. Overcoming the challenge of altering the local coordination surrounding the activators is crucial for advancing novel NIR phosphors. Here, we propose a pressure-assisted crystallographic engineering strategy to design the new Cr-doped phosphors. Implementing this approach at high temperature and pressure facilitates the phase transition from β-LiGaO2:Cr to α-LiGaO2:Cr, enabling the LiGaO2:Cr material to emit the NIR light, which was initially unattainable. Additionally, we demonstrate the in-situ monitoring of the reverse phase transition from α-LiGaO2:Cr to β-LiGaO2:Cr, validated by in-situ temperature-dependent high-resolution synchrotron X-ray diffraction. Furthermore, α-LiGaO2:Cr and β-LiGaO2:Cr exhibit unexpected optical properties characterized through synchrotron X-ray absorption, photoluminescence, temperature-dependent, and pressure-dependent analyses. Moreover, the α-LiGaO2:Cr shows strong mechanoluminescence and persistent luminescence. This research paves the way for developing novel NIR phosphors and sheds light on the analyses of pressure-assisted research.

“ μ s P-E curve” and reverse phase transition of antiferroelectric ceramics during ultra-fast charge–discharge

Antiferroelectric materials hold great potential for energy storage applications. However, a significant challenge lies in the disparity ΔW between the rapid discharge energy density Wdis and the recoverable energy density Wre. Quantitative analysis is still lacking, and the ultra-fast reverse ferroelectric–antiferroelectric (FE–AFE) transition behavior at the microsecond scale remains unknown. In this study, a pulse technique was employed instead of the Sawyer–Tower method to obtain the “μs P-E loop” during rapid charge–discharge processes. The “μs P-E curve” clearly illustrates the distinct FE–AFE transition behavior during rapid discharge in comparison to low-frequency conditions. Under pulsed conditions, the FE–AFE transition field was observed to decrease, and even a “remanent polarization” was observed, leading to a reduction in discharge energy during fast discharge. Moreover, through the enhancement of relaxor behavior and the increased diffuseness of FE–AFE switching, the μs P-E loop tended to resemble that observed at low frequencies, thereby resulting in more efficient discharge performance. This study introduced a technique for investigating the ultra-fast FE–AFE transition. Furthermore, it unveiled the origin of ΔW and provided an effective method for achieving high discharge energy density.

The effect of pre-deformation loading on the cyclic hysteresis behavior of nanocrystalline NiTi alloy：A molecular dynamic study

In this work, the effect of pre-deformation loading on the cyclic hysteresis behavior of nanocrystalline NiTi alloy is investigated by the molecular dynamic. The nanocrystalline NiTi is subjected to a large monotonic pre-deformation loading firstly to generate the irrecoverable deformation on the initial model. After this pre-deformation treatment, the other cyclic loading is exerted on the nanocrystalline NiTi to estimate the effect of pre-deformation on cyclic hysteresis behavior. The simulation results show that the plateau length of phase transition and the hysteresis loop area decreases with the increase of pre-deformation loading. When the nanocrystalline NiTi model undergoes a pre-deformation of martensite plasticity, the hysteresis curve transforms from sigmoidal-shaped to shuttle-shaped, and the MD simulation also reveals that the hysteresis behavior is gradually dominated by the dislocation motion instead of the phase transition. The corresponding micro mechanism of this degeneration of super-elasticity could be explained by the fact that the dislocations brought by the pre-deformation hinder the reverse phase transition, which results in the accumulation of residual martensite phase and disordered structure. Furthermore, the models with different grain sizes and temperatures are also considered in the MD simulation. The simulation results proved that the dislocation motion is enhanced by the temperature increase, which brings a higher hysteresis energy under a large pre-deformation loading. For the grain size effect, the reduction of the grain size leads to a higher dislocation density, which results in a more obvious phase transition degeneration phenomenon for the model with a smaller grain size.

Effect of strain rate on the microstructure evolution and superplastic deformation behavior of cold-rolled medium Mn lightweight steel

This work investigates the high-temperature tensile behavior of a Medium Mn lightweight steel (MMLS) with a chemical composition of Fe-0.3C-7.0Mn-3.5Al. The MMLS was prepared by hot-rolling followed by cold-rolling to produce a complete martensite microstructure with a high density of dislocations. The tensile tests were conducted at 800 °C within the strain rate range of 5 × 10−4 s−1-2.5 × 10−2 s−1 to explore the effect of microstructural evolution and deformation mechanism by strain rates during the tensile deformation. The results showed that the deformation behavior and mechanism of the MMLS depend not only on the initial grain size and morphology but also on the microstructure evolution during deformation. The MMLS exhibits high strain rate superplasticity (HSRS) behavior, and the deformation mechanisms are dependent on the strain rate. At lower strain rate (5 × 10−4 s−1), dislocation slip/creep is more pronounced in the γ-phase, and grain boundary sliding (GBS) is inhibited during the early deformation period, contributing to the significant texture enhancement. At moderate rate (5 × 10−3 s−1), GBS dominates deformation, while at high strain rate (2.5 × 10−2 s−1), dislocation activity and dynamic recrystallization (DRX) play a significant role. The HSRS behavior of MMLS is related to the dynamic reverse phase transition from cold-rolled ferrite to austenitic/ferrite fine-grained dual-phase structure. This work provides a theoretical basis for the development of superplastic MMLS with improved HSRS behavior and controlled the microstructure/mechanical property of component parts.

Pressure-Induced Reverse Structural Transition of Calcite at Temperatures up to 873 K and Pressures up to 19.7 GPa

In situ Raman scattering and electrical conductivity experiments have been performed to investigate the structural phase transitions of calcite during the compressed and decompressed processes in a diamond anvil cell at temperatures of 298–873 K and pressures up to 19.7 GPa. Upon compression, calcite (CaCO3-I phase) underwent three structural phase transitions from CaCO3-I to CaCO3-II phases at 1.6 GPa, from CaCO3-II to CaCO3-III phases at 2.2 GPa, and from CaCO3-III to CaCO3-VI phases at 16.8 GPa under room temperature conditions, which were evidenced by the evolution of Raman peaks, as well as the discontinuities in the pressure-dependent Raman shifts and electrical conductivity. Upon decompression, the structural phase transitions from CaCO3-VI to CaCO3-III to CaCO3-II to CaCO3-I phases took place at the respective pressures of 5.4, 1.5, and 0.4 GPa, indicating the reversibility of calcite. Furthermore, an obvious ~11 GPa of pressure hysteresis was detected in the CaCO3-VI to CaCO3-III phase transition, whereas other reverse phase transition pressures were very close to those of compressed results. At three given representative pressure conditions (i.e., 10.5, 12.5, and 13.8 GPa), a series of electrical conductivity experiments were performed at temperature ranges of 323–873 K to explore the temperature-dependent relation of CaCO3-III to CaCO3-VI structural phase transition. With increasing pressure, the transition temperature between CaCO3-III and CaCO3-VI phases gradually decreases, which reveals an obviously negative temperature-pressure relation, i.e., P (GPa) = 19.219 (±1.105) − 0.011 (±0.002) T (K). Our acquired phase diagram of calcite can be employed to understand the high-pressure structural transitions and phase stability for carbonate minerals along various subducting slabs in the deep Earth’s interior.

Reverse phase transitions in binary neutron-star systems with exotic-matter cores

Multi-messenger observations of binary neutron star mergers provide a unique opportunity to constrain the dense-matter equation of state. Although it is known from quantum chromodynamics that hadronic matter will undergo a phase transition to exotic forms of matter, e.g., quark matter, the onset density of such a phase transition cannot be computed from first principles. Hence, it remains an open question if such phase transitions occur inside isolated neutron stars or during binary neutron star mergers, or if they appear at even higher densities that are not realized in the Cosmos. In this article, we perform numerical-relativity simulations of neutron-star mergers and investigate scenarios in which the onset density of such a phase transition is exceeded in at least one inspiralling binary component. Our simulations reveal that shortly before the merger it is possible that such stars undergo a "reverse phase transition", i.e., densities decrease and the quark core inside the star disappears leaving a purely hadronic star at merger. After the merger, when densities increase once more, the phase transition occurs again and leads, in the cases considered in this work, to a rapid formation of a black hole. We compute the gravitational-wave signal and the mass ejection for our simulations of such scenarios and find clear signatures that are related to the post-merger phase transition, e.g., smaller ejecta masses due to the softening of the equation of state through the quark core formation. Unfortunately, we do not find measurable imprints of the reverse phase transition.

Диэлектрическо-спектроскопическая сепарация характеристик механизмов проводимости в нанкристаллическх пленках AgI

The study of the frequency dependence of the components of the complex permittivity of thin (100 nm) nanocrystal silver iodide (AgI) films revealed the presence of two different types of relaxation processes, sharply differing in their relaxation times: tau1<<tau2. It is established that the small relaxation time of tau1 is the time of formation of a stable configuration of the internal electric field when the external high-frequency sinusoidal electric field is shielded by a system of free conduction electrons. On the contrary, a long relaxation time of tau2 characterizes the process of shielding a low-frequency external field by a system of quasi-free silver ions. It is shown that the temperature dependence of the numerical value of tau1(T) has a thermal hysteresis with a loop, the position of the heating and cooling branches of which coincides with the temperature region of the forward and reverse phase transitions in the AgI film: semiconductor-superionic and superionic-semi-conductor. The results of calculating the parameters of dielectric spectra in the framework of Debye theory are presented, demonstrating good agreement with the parameters of the proposed electrical circuit of the film sample calculated by the complex impedance method

Hysteresis effect on austenite-martensite interface in Ni-Mn-Ga single crystal

The experiments on Ni-Mn-Ga single crystal shape memory alloy under a heating-cooling cycle demonstrate that the automatically generated twin laminate structure of the compatible austenite-martensite interface in the forward martensitic phase transition is significantly different from that in the reverse phase transition, even though the temperature hysteresis is small (As−Ms around 4 °C). Moreover, after the cooling-induced austenite → martensite transition, the remaining twin laminate is so fine (layer width around 1 μm) that the neighbouring twin boundaries merge with each other and disappear, making the fine twin laminate evolve into a single martensite variant (i.e., spontaneous detwinning). These observations provide insights into the relation between the hysteresis (phase-transition driving forces), austenite-martensite interface, and the basic material parameters such as twin boundary energy and softening modulus during the phase transition.

Macromolecular and Solution Properties of the Recombinant Fusion Protein HUG

The recombinant fusion protein HELP-UnaG (HUG) is a bifunctional product that exhibits human elastin-like polypeptide (HELP)-specific thermal behavior, defined as a reverse phase transition, and UnaG-specific bilirubin-dependent fluorescence emission. HUG provides an interesting model to understand how its two domains influence each other’s properties. Turbidimetric, calorimetric, and light scattering measurements were used to determine different parameters for the reverse temperature transition and coacervation behavior. This shows that the UnaG domain has a measurable but limited effect on the thermal properties of HELP. Although the HELP domain decreased the affinity of UnaG for bilirubin, HUG retained the property of displacing bilirubin from bovine serum albumin and thus remains one of the strongest bilirubin-binding proteins known to date. These data demonstrate that HELP can be used to create new bifunctional fusion products that pave the way for expanded technological applications.

The curvature effect in Gaussian random fields

Random field models are mathematical structures used in the study of stochastic complex systems. In this paper, we compute the shape operator of Gaussian random field manifolds using the first and second fundamental forms (Fisher information matrices). Using Markov chain Monte Carlo techniques, we simulate the dynamics of these random fields and compute the Gaussian, mean and principal curvatures of the parametric space, analyzing how these quantities change along dynamics exhibiting phase transitions. During the simulations, we have observed an unexpected phenomenon that we called the curvature effect, which indicates that a highly asymmetric geometric deformation happens in the underlying parametric space when there are significant increase/decrease in the system’s entropy. When the system undergoes a phase transition from randomness to clustered behavior the curvature is smaller than that observed in the reverse phase transition. This asymmetric pattern relates to the emergence of hysteresis phenomenon, leading to an intrinsic arrow of time along the random field dynamics.

Thermo-mechanical coupling shock waves propagation with phase transition under impact loading

In the present study, a thermo-mechanical coupling model including constitutive relation and kinetics for phase transformation is developed to study stress wave propagation in shape memory TiNi rods. The front tracking/capturing method is adopted for numerical analysis and impact experiments are performed to verify theoretical model. It is demonstrated that, a phase transition shock wave will be induced during loading due to the mixed phase hardening effect originating from the temperature dependence of transformation stress, and for unloading, double wave profile (an elastic wave and a shock wave with reverse phase transition) will be excited since the change of unloading path caused by the transient temperature rise during loading. Furthermore, shock wave propagation speeds are increased with loading stress, while driving force acting on the shock wave is supplied by shock dissipation energy, in which the temperature gradient across the shock front plays an important role. SHPB experiments show that the phase change wavefront is also a moving temperature interface, which will have an important influence on the stress wave structure. Taylor impact experiments show that the proposed kinetic relation in this paper is in good agreement with the experimental results, which reflects the intrinsic characteristic of materials with strong nonlinear thermo-mechanical coupling behavior.

Thermokinetic EMF during a reverse phase transition in titanium nickelide as a way of information recording

The external factors that influence on the thermokinetic EMF value in the Ti – 50 at.% Ni samples were determined. A method for setting thermokinetic EMF in certain sections of the TiNi wire was developed. The thermokinetic EMF value was measured directly using a digital millivoltmeter MNIPI V7-72. The sections of the Ti – 50 at.% Ni wire samples were subjected to tensile tests on a tensile machine IP 5158-5. On the basis of calorimetric studies, the kinetics of martensitic transformations was investigated. It was found that the direct phase transition affects the thermokinetic EMF value of the Ti – 50 at.% Ni during thermal cycling. Thermal cycling in the temperature range of the complete martensitic transformation causes the thermokinetic EMF value reduction by 0.16 mV by the 15th temperature cycle. The degradation of the thermokinetic EMF value by 0.04 mV took place during thermal cycling in the temperature range of the incomplete martensitic transformation by the 70th thermal cycle. The thermokinetic EMF value was restored to 0.22 mV with increasing temperature to 240 °С, as in the case of annealing at temperatures of 400÷800 °С. The thermokinetic EMF value is associated with a change in physical and mechanical properties of the alloy during thermal cycling. It is characterized by a change in stages of the phase transition and a shift of the characteristic temperatures. On the basis of the obtained experimental data, a method was proposed for a purposeful setting of extended TiNi wire sections with the thermokinetic EMF value from 0 to 0.6 mV, using different methods of influence on its value (thermal cycling, deformation, temperature change in heating zone). The proposed technical solution can be used as a method for information recording.

Seismic anisotropy, dominant slip systems and phase transitions in the lowermost mantle

SUMMARY The presence of seismic anisotropy at the base of the Earth's mantle is well established, but there is no consensus on the deformation mechanisms in lower mantle minerals that could explain it. Strong anisotropy in magnesium post-perovskite (pPv) has been invoked, but different studies disagree on the dominant slip systems at play. Here, we aim to further constrain this by implementing the most recent results from atomistic models and high-pressure deformation experiments, coupled with a realistic composition and a 3-D geodynamic model, to compare the resulting deformation-induced anisotropy with seismic observations of the lowermost mantle. We account for forward and reverse phase transitions from bridgmanite (Pv) to pPv. We find that pPv with either dominant (001) or (010) slip can both explain the seismically observed anisotropy in colder regions where downwellings turn to horizontal flow, but only a model with dominant (001) slip matches seismic observations at the root of hotter large-scale upwellings. Allowing for partial melt does not change these conclusions, while it significantly increases the strength of anisotropy and reduces shear and compressional velocities at the base of upwellings.

Probing the lattice structure of dynamically compressed and released single crystal iron through the alpha to epsilon phase transition

Experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1 μm thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 100 J, 10 ns duration laser pulse incident on the polyimide ablator was used to shock compress the iron samples to initial stresses greater than 25 GPa, exceeding the ∼13 GPa alpha (body-centered-cubic or bcc structure) to epsilon (hexagonal-close-packed or hcp structure) phase transition stress. XRD measurements were performed at various times relative to the shock wave entering the iron sample: early times, <∼150 ps while the initial shock waves propagated through the iron; intermediate times, after the iron equilibrated with the ablator and window reaching a plateau stress state (12 or 17 GPa) lasting several nanoseconds; and late times, during uniaxial strain release. The early time measurements show that in <∼150 ps, the high-pressure hcp phase is relaxed with a c/a ratio of 1.61, contrary to previous laser shock experiments where a c/a ratio of 1.7 was inferred. In the plateau stress state and partially released states, XRD measurements showed that the hcp structure retained a c/a ratio of 1.61 with no observable changes in the microstructure. Upon stress release at ∼1 GPa/ns release rate, the reverse phase transition (hcp to bcc) to the original single crystal orientation (implying a transformation memory effect) was observed to reach completion somewhere between 13 and 11 GPa, indicating little stress hysteresis under rapid uniaxial strain release. A similar memory effect for the reverse hcp to bcc transformation has been previously observed under hydrostatic compression. However, the bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism.

Kinetics of iron α-εphase transition under thermodynamic path of multiple shock loading-unloading

The dynamics of iron under extreme conditions like high temperature and high pressure has been well studied for several decades. But, there have been not many reports about the phase transition kinetics coupled with complicated thermodynamic paths, especially loading-unloading-reloading path, which is closer to the real applications. A three-layer structure impactor with five stages performed in the front-surface experiment is made up to approach the special path. We choose epoxy to be the adhesive as it has low impedance and high strength. Tantalum, the standard material of high impedance which also has single wave structure, is selected for reloading process. The wave profile shows a 3-wave structure in the first unloading period and the inverse phase transition threshold is calculated to be about 11.3 GPa. This onset pressure of reverse phase transition is not consistent with Barker’s result, higher than his result (about 2.5 GPa). By comparing with recalculated result of Jensen’s data, we find that our result is consistent with theirs.In this work the inverse phase transition ends at about 10 GPa, the value from this way which is higher than Barker’s finding, even higher than his result of the threshold pressure of reverse phase transition. And at this state there remains 12%–15% of ε phase. So it cannot be seen as the completed reverse phase transformation. The phase transition onset pressure is 10–12 GPa on the reloading path and it is about 1–2 GPa lower than the first phase transition. By simulating the wave profile, the discrepancy of using different phase transformation characteristic time <i>τ</i> as 30 ns and 5 ns is analyzed. It can be seen that the phase transition rate of reloading is faster than that of the first loading process. These phenomena may be caused by the twins and the dislocations which are produced by the inverse phase transition. Also, as unloading time becomes longer, the mass fraction of ε phase becomes lesser and the onset pressure of α → ε phase transition becomes lower. This because with more ε phases transforming into α phase, more twins and dislocations will be produced in material. Therefore, it brings the lower onset pressure.

Influence of heat treatment on thermokinetic EMF during reverse phase transition in titanium nickelide

The effect of duration and annealing temperature in the range of 400–800 °C on the thermokinetic EMF value in titanium nickelide, the composition of which is close to the equi-atomic one, at a reverse phase transition was investigated. Thermokinetic EMF was measured directly using a digital millivoltmeter MNIPI V7-72. The phase and elemental composition of the alloy and the kinetics of thermoelastic phase transformations have been checked by X-ray diffraction and calorimetric studies, and X-ray microanalysis. Annealing at temperatures of 500 and 800 °C leads to an increase in the thermokinetic EMF value from 0.22 to 0.25 mV. Removal of the oxide layer from the sample surface annealed at 700 °C for 0.5 h leads to an increase in the thermokinetic EMF value from 0.22 to 0.26 mV for the 1-st thermal cycle. It was found that thermal cycling causes a decrease in the thermokinetic EMF values down to 0.98 mV for the 20th thermal cycle for the samples without an oxide layer and to 0.3 mV for the samples with an oxide layer, respectively. With the increase in annealing time up to 20 h at 700 °C, the decrease in the thermokinetic emf value to 0.16 mV was observed. The thermokinetic EMF value after heat treatment is associated with changes in the physical and mechanical properties of the alloy and characterized by a shift of the characteristic temperatures of the phase transition. The research results are important for understanding the physics of thermoelectric phenomena in shape memory alloys during nonstationary heating and can be used both to control the homogeneity of their physical and mechanical properties and to design smart actuators and sensors, mechanisms of control systems.

Spinodal decomposition influence of austenite on martensitic transition in a Mn-13 at.%Cu alloy

The effect of ageing regimes at temperatures in a range from 400 °C to 520 °C and time for up to 120 h on the spinodal decomposition of austenite in an as-quenched Mn–13Cu alloy is investigated using small-angle neutron scattering and in situ neutron diffraction. The as-quenched from 850 °C alloy has a 100% antiferromagnetic martensitic structure that can be described as a face-centered tetragonal (f.c.t.) lattice at room temperature (RT). In the early stage of the ageing process (for 8 h at 400–480 °C or for the first 16 h at 440 °C), the decomposition of the high-temperature face-centered cubic (f.c.c.) phase into an Mn-rich f.c.c. matrix and Cu-rich clusters takes place. Higher ageing temperature or longer ageing time leads to the formation of α-Mn inclusions with a body-centered cubic (b.c.c.) structure, retained after cooling to RT. Martensitic transition temperatures strongly depend on the ageing temperature and time, i.e., on the degree of chemical decomposition in austenite. The linear relationship between phase transition temperatures and Mn content in the matrix is quantitatively established. The thermal hysteresis between a direct and reverse phase transition does not change with ageing treatment. According to the in situ neutron diffraction results, structural and magnetic transitions occur at the same temperature during heating and cooling.

Stability of Shape Memory Alloy rods under reverse phase transformation in case of initial tensile phase-structural strains

Stability of a round cross section rod of Shape Memory Alloys under reverse phase transition where the initial strain was obtained with the help of reverse loading and subsequent unloading was investigated. It was shown that the additional structural transformation connected with buckling could not take place within the framework of a given model of the constitutive equations for Shape Memory Alloys. Numerical solutions in various problem statements and concepts were obtained.

2D Derivative Phase Induced Growth of 3D All Inorganic Perovskite Micro–Nanowire Array Based Photodetectors

AbstractA large number of derivative phases in inorganic perovskites are reported with special structures and extraordinary performances in photoelectronic device applications. The reverse phase transition between derivative phases and perovskites usually induces recrystallization or forms mixed components. In this work, derivative phase‐induced growth of the CsPbBr3 micro–nanowire (MW) array by utilizing phase transition of the 2D CsPb2Br5 phase is reported. Owing to its layered structure and phase transition, annealing of CsPb2Br5 at a temperature of 550 °C combined with solvent quenching leads to a templating effect to form a high‐quality CsBr MW array. Subsequent PbBr2 deposition and the second annealing are employed to form aligned CsPbBr3 MW arrays. Based on this method, a CsPbBr3 MW array‐based photodetector is fabricated. The large grain size, less grain boundaries, and lower surface potential of the CsPbBr3 MW array lead to high device performance with a responsivity of 7.66 A W−1, a detectivity of ≈1012 Jones, and long‐term operational stability over 1900 min.