Observation Of Phase Transition Research Articles

High-P–T impedance measurements using a laser-heated diamond anvil cell

The electrical conductivity (EC) of minerals found on Earth and throughout the solar system is a fundamental transport property that is used to understand various dynamical phenomena in planetary interiors. High-pressure and high-temperature (P-T) EC measurements are also an important tool for observing phase transitions. Impedance measurements can accurately measure the EC of a nonmetallic sample. In previous measurements under static conditions using a laser-heated diamond-anvil cell (LHDAC), only direct current resistance is measured, but this method overestimates the bulk sample resistance. Moreover, the previous methodology could only be applied to nontransparent samples in an LHDAC using infrared lasers, limiting the range of measurable composition. To the best of our knowledge, no in situ high-P-T EC measurements of transparent materials have been reported using LHDAC techniques. We developed a novel impedance measurement technique under high-P-T conditions in an LHDAC that applies to transparent samples. As a validation, we measured the EC of Mg0.9Fe0.1SiO3 bridgmanite up to 51GPa and 2000K and found that the results are consistent with those of previous studies. We also measured the EC values of sodium chloride to compare with those of previous studies, as well as those of cubic boron nitride and zirconia cement to quantify how well they insulate under high P-T conditions. This is the first report of the impedance and EC measurements of transparent minerals in an LHDAC, which allows the measurement of Fe-poor/-free materials, including the major constituents of the interiors of gas giants and icy planets, under extreme conditions.

Experimental data and thermodynamic modeling of the CO2 + Acetone + Efavirenz system at high pressures

It is important to understand the fluid phase behavior of the systems containing CO2, acetone, and Efavirenz for processes that use supercritical fluids to produce micro and/or nanoparticles for drug encapsulation. Thus, the purpose of this work is to measure experimentally data on the phase transitions of CO2 + Efavirenz and CO2 + acetone + Efavirenz systems using the visual static synthetic method and a variable-volume cell integrated into the experimental equipment. The experimental settings for the binary system were: pressures up to 16 MPa, temperatures of 333.15, 338.15, and 343.15 K, and the global Efavirenz mole fraction from 4 × 10−5 up to 15 × 10−5. The experimental settings for the ternary system were: pressure up to 10 MPa, temperatures from 303.15 to 333.15 K, and the global CO2 mole fraction from 0.2 up to 0.9. For the binary systems, the observed phase transitions are solid–fluid transitions; for the ternary systems, the observed phase transitions are bubble point (BP) transitions. Thermodynamic simulations using the Group Contribution Volume-Translated Peng-Robinson (GC-VT-PR) and Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state (EoS) demonstrated a striking correlation with experimental data. The relative deviations from pressure and temperature corroborate the efficiency of the thermodynamic models used in this work.

Shock wave induced conformational phase transition of L-leucine

Systematic shock wave recovery studies on materials are very much needed for a deeper understanding of the role of hydrogen bonds and their stability at dynamic shocked conditions, especially on amino acid. In the present investigation, one of the simplest amino acids and potentially an important non-linear optical material of l-α-Leucine (C6H13NO2) powder samples have been chosen so as to assess the crystallographic phase stability by employing powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) techniques. Remarkably, the test sample undergoes a conformational phase change from phase-I (low-temperature P21) to phase –II (high-temperature P21) at the 50 shocked conditions whereas phase-II remains to be stable up to 200 shocks and the observed phase transition is interpreted and compared with the previously reported article (Facanha Filho et al., Phys. Chem. Chem. Phys., 2011, 13, 6576–6583). It could be considered that the observed phase is due to the conformational changes occurring in the sample.

Phase Transitions for One-Dimensional Lorenz-Like Expanding Maps

Given an one-dimensional Lorenz-like expanding map we describe a class \({\mathcal {A}}\) of potentials \(\phi :[0,1]\longrightarrow {\mathbb {R}}\) admitting at most one equilibrium measure and we construct a family of continuous but not weak-Hölder continuous potentials for which we observe phase transitions. This give a certain generalization of the results proved in Pesin and Zhang (J Stat Phys 122(6):1095–1110, 2006), where the authors have proved this for a smaller class of potentials, that is, for uniformly expanding maps and weak-Hölder continuous potentials. Indeed, the class \({\mathcal {A}}\) form an open and dense subset of \(C([0,1],{\mathbb {R}})\), with the usual \({\mathcal {C}}^0\) topology.

Quantum Phase Transition in the Spin Transport Properties of Ferromagnetic Metal-Insulator-Metal Hybrid Materials.

Perpendicular magnetic tunnel junctions provide a technologically important design platform for studying metal-insulator-metal heterostructure materials. Accurate characterization of the sensitivity of their electronic structure to proximity coupling effects based on first-principles calculations is key in the fundamental understanding of their emergent collective properties at macroscopic scales. Here, we use an effective field theory that combines ab initio calculations of the electronic structure within density functional theory with the plane waves calculation of the spin polarised conductance to gain insights into the proximity effect induced magnetoelectric couplings that arise in the transport of spin angular momentum when a monolayer tunnel barrier material is integrated into the magnetic tunnel junction. We find that the spin density of states exhibits a discontinuous change from half-metallic to the metallic character in the presence of monolayer hexagonal boron nitride when the applied electric field reaches a critical amplitude, and this signals a first order transition in the transport phase. This unravels an electric-field induced quantum phase transition in the presence of a monolayer hexagonal boron nitride tunnel barrier quite unlike molybdenum disulphide. The role of the applied electric field in the observed phase transition is understood in terms of the induced spin-flip transition and the charge transfer at the constituent interfaces. The results of this study show that the choice of the tunnel barrier layer material plays a nontrivial role in determining the magnetoelectric couplings during spin tunnelling under external field bias.

Temperature‐Dependent Phase Transitions in HfxZr1‐xO2 Mixed Oxides: Indications of a Proper Ferroelectric Material

AbstractKnowledge about phase transitions in doped HfO2 and ZrO2‐based films is crucial for developing future ferroelectric devices. These devices should perform in ambient temperature ranges with no degradation of device performance. Here, the phase transition from the polar orthorhombic to the nonpolar tetragonal phase in thin films is of significant interest. Detailed electrical and structural characterization is performed on 10 nm mixed HfxZr1‐xO2 binary oxides with different ZrO2 in HfO2 and small changes in oxygen content. Both dopant and oxygen content directly impact the phase transition temperature between the polar and nonpolar phase. A first‐order phase transition with thermal hysteresis is observed from the nonpolar to the polar phase with a maximum in the dielectric constant. The observed phase transition temperatures confirm trends as obtained by DFT calculations. Based on the outcome of the measurements, the classification of the ferroelectric material is discussed.

Phase Transitions of BiVO4 under High Pressure and High Temperature

We have studied the occurrence of phase transitions in two polymorphs of BiVO4 under high-pressure and high-temperature conditions by means of X-ray diffraction measurements. The fergusonite polymorph undergoes a phase transition at 1.5(1) GPa and room temperature into a tetragonal scheelite-type structure. The same transition takes place at 523(1) K and ambient pressure. A second phase transition takes place at room temperature under compression at 16(1) GPa. The transition is from the tetragonal scheelite structure to a monoclinic structure (space group P21/c). All observed phase transitions are reversible. The zircon polymorph counterpart also transforms under compression into the scheelite-type structure. In this case, the transitions take place at 4.3(1) GPa and room temperature and at 653(1) K and ambient pressure. The zircon–scheelite transition is nonreversible. The experiments support that the fergusonite–scheelite transformation is a second-order transition and that the zircon–scheelite transformation is a first-order transition. Finally, we have also determined the compressibility and the thermal expansion of the fergusonite, scheelite, and zircon phases.

3D pattern formation from coupled Cahn-Hilliard and Swift-Hohenberg equations: Morphological phases transitions of polymers, bock and diblock copolymers

This work proposes a new mathematical model of a ternary mixture composed of coupled Cahn-Hilliard and Swift-Hohenberg equations solved in three dimensions (3D) through a pseudo-spectral implicit method (a numerical method of the fast Fourier transform). The 3D numerical solutions dynamic is analyzed through its structure factor and growth law to study its behavior and some observed phase transitions. These numerical solutions evolve into glassy and crystalline phases in the form of 3D patterns. The new model has a free energy functional that considers small monomers of polymer (or copolymeric) chains taken into the Edwards free energy, as well as solvent-monomers and solvent-stretch free energies whose dynamic is given by the Cahn-Hilliard and Allen-Cahn equations. Isotropic and anisotropic phases from polymers, block, and diblock copolymers blend such that these phases have a morphological diversity of classical and complex structures. As an application of the dynamics of the new ternary model, it has a diversity of morphologies which allows obtaining porous polymeric materials manufactured by a novel 3D printing technique: the mathematical design process and 3D printing assisted manufacturing (MDP-3DPAM). This method allows the proposal of a new technique for the design and creation of polymeric materials with controlled pore size distribution starting with computational modeling.

Quantum Dot Phase Transition Simulation with Hybrid Quantum Annealing via Metropolis-Adjusted Stochastic Gradient Langevin Dynamics

We report a hybrid quantum-classical simulation approach for simulating the optical phase transition observed experimentally in the ultrahigh-density type-II InAs quantum dot array. A hybrid simulation scheme, which contains stochastic gradient Langevin dynamics (a well-known Bayesian machine learning algorithm for big data) along with adiabatic quantum annealing, is developed to reproduce the experimentally observed phase transition. By implementing the simulation scheme into a quantum circuit, we successfully verified the phase transition observed in the experiment. Our work demonstrates for the first time the feasibility of hybridizing quantum computation with classical Langevin dynamics for the analysis of carrier dynamics and quantum phase transition of the quantum dot.

Critical field analysis and magnetic properties of perovskite manganese oxide La0.8Ca0.2Mn1-xNixO3(x = 0.0,0.1,0.2)

Critical field analysis and the magnetocaloric effect of the polycrystalline perovskite manganese oxide samples, La0.8Ca0.2Mn1-xNixO3 (x = 0.0,0.1,0.2), which were prepared using a traditional solid phase reaction method, were explored. The data obtained from X-ray diffraction (XRD) measurements of the polycrystalline samples show good single-phase properties. The replacement of a given Mn3+ ion fraction by Ni2+ions decreased the crystal parameters and unit cell volume, Curie temperature (Tc), and the magnetic and the magnetic entropy change. These property changes originate from the partial substitution of Mn3+ ions by Ni2+, which changes the Mn3+/Mn4+ ratio and consequently weakens the double exchange (DE) effect. At an applied magnetic field of 7 T, the maximum difference in magnetic entropy of the undoped sample is 6.15 J/kg•K, and the refrigeration efficiency is 422.94 J/kg. The critical parameters of the parent material and the doped sample fit well to the Tricritical model. The La0.8Ca0.2Mn1-xNixO3 samples with x = 0.0 exhibit crossover of the phase transitions, which can be first or second order. The observed phase transitions of samples with x = 0.1 and 0.2 are exclusively second order. Around the TC of La0.8Ca0.2Mn1-xNixO3 (x = 0.0, 0.1 and 0.2) compounds, the correlation of the magnetic field with the maximum change in magnetic entropy follows a power law.

Enabling direct CO2 electrolysis by alkali metal cation substituted membranes in a gas diffusion electrode reactor

Direct gas phase electrolysis using a membrane electrode assembly (MEA) reactor has been recognized as a promising direction for large scale continuous CO2 conversion. The so called “zero-gap” CO2 reduction was however seldom achieved when proton is the main charge carrier in the system due to the overwhelmed competing hydrogen evolution reaction (HER) taking place at the cathode. In this work, the suppression of HER is achieved by regulating the rate of proton transport through the membrane electrolytes and is realized by the modification of the sulfonic acid side chains with alkali metal cations. The MEA’s CO2 reduction reaction (CO2RR) faradaic efficiency (CO2RR-FE) is significantly improved as the alkali cations are varied sequentially from Li to Cs. Such improvement is attributed to the significantly hindered proton transport in the Cs-MEA, as reflected by the substantially larger high frequency resistance (HFR), which leads to enhanced competitive adsorption of CO2 on the copper catalyst. In addition, the Cs-MEA showed the highest robustness for both the membrane cations and the copper cathode against leaching and corrosion. Moreover, the observed phase transition of copper metal into faceted cuprous oxide crystals exposing low index surfaces also favors CO2RR over HER. The collective desirable properties of the Cs-MEA result in the best CO2RR performance, exhibiting a maximum CO2RR-FE of 0.44% at −1.2 V vs RHE and a space time yield (STY) of 1.06 mmol·h−1·gcat-1 for methane (CH4) and 2.02 mmol·h−1·gcat-1 for carbon monoxide (CO).

Investigation of ferroelectric phase transitions in TlZnPO4 stuffed tridymite compound

This study elucidates both structural and physical behaviors of Thallium–Zinc Orthophosphate (TlZnPO4) compound via solid-state reaction. Advanced analytical techniques were performed to study the microstructure and investigate the existence of phase transitions in this material. Raman and impedance spectroscopy were studied to understand the behavior of the studied material and to determine its vibrational and electrical properties. At room temperature, the XRPD analysis confirmed that the synthesized material could be satisfactorily indexed using a P21 space group of the monoclinic unit cell. DSC analysis reveals the existence of two reversible phase transitions at T1 ​= ​546/498 ​K and T2 ​= ​646/600 ​K (Heating/Cooling). The first combine both order-disorder and displacive mechanism, while the second is displacive. SEM analysis reveals that the grains size is in the micrometric scale. Raman, as well as impedance spectroscopy analysis, proved the existence of two phase transitions. These transitions arise from the rotation of both ZnOn (n = 4, 5) and PO4 in the opposite direction. This rotation provokes a change in coordination of Zn atoms from ZnO5 to ZnO4, achieving higher symmetry. The electrical study confirmed the existence of a non-Debye type relaxation attributed to the grain contribution. The dielectric study proved that the observed phase transitions are ferroelectric.

First-order phase transition in nanotubular titanium dioxide

Titanium dioxide (TiO2) nanotubes array with the length of 16 μm and the outer diameter of 100 nm were synthesized by anodic oxidation of titanium foil in an electrolyte solution containing a fluorine-containing solution of ethylene glycol. The selected synthesis conditions make it possible to separate the nanotubular array from the titanium foil and study it as a homogeneous functional material. The performed scanning electron microscopy study and Brunauer--Emmett--Teller analysis allowed to get data on the morphology of the samples. X-ray diffraction, thermogravimetric, and differential scanning calorimetry analysis made it possible to determine the temperature of the phase transition of the amorphous state into crystalline anatase (sp.gr. I4/amd). Observed phase transition of first order takes place at temperature about 350oC. Keywords: nanotubular titanium dioxide films, anodic oxidation, phase transition, anatase, TG, DSC.

Effect of Interactions between Vehicles and Mid-Block Crosswalks on Traffic Flow and CO2 Emission

Unsignalized mid-block raised crosswalks have been adopted as inclusive transport strategies, providing humps to reduce vehicles’ speed to promote drivers to yield to pedestrians. The interaction between vehicles and pedestrians can induce local jams that can merge to become a gridlock. The purpose of this paper is to investigate the interaction between vehicles and the mid-block raised crosswalk, analyzing its effects on traffic flow, instantaneous CO2 emissions, and energy dissipation. A pedestrian–vehicle cellular automata model was developed, where a single-lane road with a mid-block raised crosswalk is considered. The lane boundaries were controlled with the injections rate (α) and extraction rate (β), while the pedestrians’ entrance was controlled with the rate (αp). The system’s phase diagram was constructed, identifying four phases: maximum current, jamming, congestion, and gridlock. All observed phase transitions are of the second order. The transition from maximum current (or jamming) phase to gridlock phase is not noticed. Moreover, since the crosswalk is a bottleneck, the gridlock phase takes place when the pedestrians’ influx exceeds a critical value (αp > 0.8). The study also revealed that the crosswalk is the main precursor of energy dissipation and CO2 emissions, whose major effects are observed during the jamming phase.

Characterization of an Al-Cu-Mg-Zn multi principal element alloy by experimental and computational screening methods

We present a combined experimental and computational investigation of phase stability and mechanical properties in the Al-Cu-Mg-Zn quaternary system. Samples containing different relative compositions were prepared using magnetron sputtering and investigated by electron microscopic and X-ray based methods. To classify the technical relevance of the samples, the indentation hardness was measured. The phase stability was studied computationally using a cluster expansion approach based on density functional theory (DFT) methods in a comprehensive screening of the structural and stoichiometric configuration space. Upon decreasing Cu concentration, a transition from an FCC to a mixed FCC/BCC crystal system and significant changes in the mechanical properties depending on Valence Electron Concentration (VEC) and atomic size differences (δr) was observed experimentally. The corresponding crystallographic phases were assigned by XRD and the experimentally observed phase transition was confirmed by the computational screening of formation energies. Since to date, quaternary complex light metal alloy systems cannot be reliably predicted, this is an important step towards a priori modelling of this class of materials.

On the Origin of Zero Interface Resistance in the Li6.25Al0.25La3Zr2O12|Li0 System: An Atomistic Investigation.

Understanding the nature of ion transfer at the interface between Li metal and solid electrolytes (SE) is essential for further optimization of all-solid-state Li-ion batteries. Thus, the Li transfer across the SE|Li metal interface is investigated by means of ab initio calculations based on density functional theory in this work. The aluminum-doped garnet Li6.25Al0.25La3Zr2O12 (LLZO) is considered as a model SE due to its practical stability against Li metal. A low-energy interface model in bicrystal geometry is constructed and investigated by nudged elastic band calculations as well as ab initio molecular dynamics (AIMD) simulations. In order to distinguish between interface and bulk transport in the AIMD simulations, a post-processing protocol is developed. We find that the activation energies and diffusivities of Li are comparable in bulk LLZO and across the interface, substantiating that the interface kinetics are not rate-limiting. Moreover, electronic structure analysis indicates that charge transfer occurs gradually. Finally, Al3+ loss of LLZO at the interface rationalizes the experimentally observed phase transition from cubic to tetragonal observed close to Li metal contacts.

High resolution study of the n = 7–9 p,p’-n-alkylazobenzenes phase transitions by photopyroelectric and adiabatic scanning calorimetries

A study of phase transitions of photochromic p,p’-n-alkylazobenzenes compounds was carried out by means of adiabatic scanning calorimetry (ASC) and photopyroelectric calorimetry (PPE) techniques, yielding accurately the temperature dependence of the enthalpy and of the specific heat capacity across the observed phase transitions, and the corresponding enthalpy of transition values. In addition, polarization microscopy imaging of the sample texture was performed together with the PPE calorimetric evaluations to establish the nature of the involved phases. By performing PPE calorimetric evaluations during UV irradiation of the samples, the influence of the photoinduced trans to cis isomerization of the nAB molecules on the occurrence of the phase transitions was assessed.

Segregation on the nanoscale coupled to liquid water polyamorphism in supercooled aqueous ionic-liquid solution.

The most intriguing hypothesis explaining many water anomalies is a metastable liquid-liquid phase transition (LLPT) at high pressure and low temperatures, experimentally hidden by homogeneous nucleation. Recent infrared spectroscopic experiments showed that upon addition of hydrazinium trifluoroacetate to water, the supercooled ionic solution undergoes a sharp, reversible LLPT at ambient pressure, possible offspring of that in pure water. Here, we calculate the temperature-dependent signature of the OH-stretching band, reporting on the low/high density phase of water, in neat water and in the same experimentally investigated ionic solution. The comparison between the infrared signature of the pure liquid and that of the ionic solution can be achieved only computationally, providing insight into the nature of the experimentally observed phase transition and allowing us to investigate the effects of ionic compounds on the high to low density supercooled liquid water transition. We show that the experimentally observed crossover behavior in the ionic solution can be reproduced only if the phase transition between the low- and high-density liquid states of water is coupled to a mixing-unmixing transition between the water component and the ions: at low temperatures, water and ions are separated and the water component is a low density liquid. At high temperatures, water and ions get mixed and the water component is a high-density liquid. The separation at low temperatures into ion-rich and ion-poor regions allows unveiling the polyamorphic nature of liquid water, leading to a crossover behavior resembling that observed in supercooled neat water under high pressure.

Stepwise Stress-Induced Transformations of Metal-Organic Polyhedral Cluster-Based Assemblies: Where Conformational and Supramolecular Features Meet.

Understanding the factors governing the formation of supramolecular structures and phase transitions between various forms of molecular crystals is pivotal for developing dynamic, stimuli-responsive materials and polymorph-controlled syntheses. Here, we investigate the pressure-induced dynamic of both the intrinsic molecular structure and the supramolecular network of a predesigned polyhedral oxo-centered zinc cluster incorporating monoanionic N,N'-diphenylformamidinate and featuring N-bonded phenyl groups in close proximity to the primary coordination sphere. We demonstrate that the model oxo cluster is prone to undergoing pressure-induced conformational transformations of the secondary coordination sphere and simultaneous stepwise (initially every second polyhedral molecule undergoes the conformational transformations) and reversible transitions from an ambient phase α to high-pressure phases β and γ, as single-crystal-to-single-crystal events. The observed phase transitions illustrate the key role of an interplay between the low-energy conformation perturbations and cooperative intra- and intermolecular noncovalent interactions.

Antiperovskite K3OI for K-Ion Solid State Electrolyte.

Discovering new K-ion solid-state electrolytes is crucial for the emerging K-batteries to improve energy density, cycle life, and safety. Here, we present a combined experimental and theoretical study of antiperovskite K3OI as a K-ion solid-state electrolyte. A solid-solid phase transition at approximately 240 °C induces an increase in ionic conductivity by 2 orders of magnitude. Anion disorder in the I-O sublattice is found to be a potential mechanism for the observed phase transition. The Ba-doped K3OI sample K2.9Ba0.05OI achieves 3.5 mS cm-1 after the phase transition with a low activation energy of 0.36 eV. Stable cycling of K/K2.9Ba0.05OI/K symmetric cells are observed with a low overpotential of 50 mV at 0.5 mA/cm2 at 270 °C. This study not only reports K3OI as a promising K-ion solid-state electrolyte that is compatible with reactive K metal but also improves the understanding of alkali antiperovskite solid-state electrolytes in general.