Structural Phase Change Research Articles

(AlCrMoTiNi)1-XNX high entropy ceramic with high hardness and toughness prepared by co-filtered cathodic vacuum arc deposition

High entropy ceramic (HEC) coatings have become candidates for new protective coating due to their high strength. However, the hardness - toughness balance of the ceramic coatings is still a difficult problem to solve. The strong nitride forming elements Al, Ti, Cr, Mo, and the non-nitride forming element Ni were selected as the components of the (AlCrMoTiNi)1-XNX HEC coatings to regulate the hardness and toughness. When x = 0 and 0.29, the composite structure of amorphous and metallic Ni phase is observed in these coatings. When x = 0.37, 0.40, and 0.45, the phase structure changes to the composite structure of nanoscale face-centered cubic (FCC) phase, metallic Ni, and amorphous phase. When x = 0.45, the maximum hardness of the HEC coating is 31.25 GPa, and it also has high toughness with a KIC value of 3.25 MPa m1/2. The HEC coating with high hardness and toughness also presents excellent wear resistance and corrosion resistance. Therefore, the (AlCrMoTiNi)0.55N0.45 HEC coating has potential as a protective coating applied in various areas.

Theoretical Investigation of Pressure Dependent Structural and Elastic Properties of MnSi Compound

MnSi is a metallic compound that exhibits a structural phase transition as a function of pressure. At ambient conditions, MnSi has a cubic structure such as NaCl type crystal structure. However, at high pressures, it undergoes a structural phase transition to a CsCl type crystal structure. The pressure-dependent structural phase transition in MnSi has been studied using various experimental and theoretical techniques. In the present work, we have used an efficient inter-ionic potential approach to predict pressure dependent structural phase change and associated volume collapse in MnSi. Therein, the potential includes the long-range Coulomb, van der Waals (vdW) interaction, and the short-range repulsive interaction up to second neighbour ions. It has been demonstrated that the Hafemeister and Flygare approach successfully evaluates the equation of state for change in volume with respect to applied pressure. We have identified a structural phase transition from B1(NaCl) type structure to B2 (CsCl) type structure in this compound. The estimated value of phase transition pressure (Pt) is 42 GPa, which is consistent with the available reported data. The identified first order phase transformation showed a volume collapse of about 10% in the vicinity of transition. In addition, we have also investigated second order of elastic constants for MnSi compound.

Visible-light-assisted PMS activation by heterojunction photocatalyst MgIn2S4/Bi2O3 for tetracycline degradation

Composite MgIn2S4/Bi2O3 was prepared and applied to the photocatalytic degradation of tetracycline (TC) under visible light. Results showed that formation of type-II heterojunction extended the visible light response range of the composite to 628 nm, effectively limiting the rapid recombination of photogenerated carriers. Further, the degradation experiment showed that TC was effectively decomposed by the composite. The main active substances for degrading TC were SO4·−, ·OH, h+ and 1O2. Cycling experiments showed that the TC removal rate by MgIn2S4/Bi2O3 photocatalytic material was still as high as 75% after 4 cycles without any obvious changes in the crystalline phase structure.

Structural, relaxor behavior, and energy storage performance of BaTiO3–Bi (Mg2/3Nb1/3)O3 solid solutions for potential MLCC application

In the discussed work, (1-x) BaTiO3 (BT)-x Bi(Mg2/3Nb1/3)O3 (BMN) solid-combinations have been synthesized via the solid-state process; and both corresponding dielectric and ferroelectric behavior have been learned for possible Multilayer Ceramic Capacitor (MLCC) applications. The phase confirmation has been identified utilizing X-ray diffraction; and Rietveld refinement technique has been used for structural analysis that unveils the formation of pure perovskite structure of the prepared ceramics. Rietveld refinement results reveal the structural changeover from tetragonal to pseudo-cubic for x≥0.125. Raman spectroscopy measurements confirm the structural phase changes and lattice modifications due to the chemical substitutions. Microstructural analysis has been done with the help of electron micrograph. Dielectric performance of the synthesized (1-x)BaTiO3(BT)-xBi(Mg2/3Nb1/3)O3(BMN) solid solutions has been examined within a temperature range of 173K–473K at different applied frequencies. A broad phase transition and relaxor character is detected from dielectric investigation. The relaxor behavior has been quantified by the Vogel-Fulcher fitting. The thermal stability of the prepared samples was calculated by means of standard formula of Temperature Coefficient of Capacitance (TCC). Hysteresis loop was undertaken to identify the ferroelectric properties and energy storage capacity. Among all the compositions, x = 0.10 shows good thermal stability, an elevated recoverable energy density; and a remarkable efficiency that makes it suitable for MLCC applications.

Wear suppression and interface properties of diamond tool in micro-milling of TC4 alloy under graphene nanofluid MQL environment

The sustainable micro-milling process of TC4 alloy has garnered significant attention in aerospace engineering. However, the poor machinability of TC4 alloy results in particularly severe tool wear. Tool wear directly affects the machining quality of the parts, and traditional cutting fluids of suppressing tool wear indirectly increase production costs and pollute the environment. Therefore, to suppress the negative effects caused by tool wear, this paper proposes the application of water-based graphene nanofluid in the micro-milling of TC4 alloy in diamond tools. Firstly, micro-milling experiments and molecular dynamics simulations were conducted in different environments, including dry and water-based graphene nanofluid environments. Finally, tool surface wear morphology, milling forces, surface elements and structural phase changes were compared in detail. The results show that tool wear, including adhesive wear, abrasive wear, and edge chipping, was suppressed by graphene nanofluids compared to dry conditions, thereby increasing tool life. The graphene nanofluid improved the contact state between the tool and workpiece interface, reducing the milling forces. In addition, molecular dynamics indicates that the catalytic effect of the transition elements in the workpiece on the diamond tool was also weakened, and the carbon atoms of graphene were used as a sacrificial source to balance the catalytic effect. Graphitization and diffuse wear of the diamond were suppressed. More importantly, the water-based graphene nanofluid not only improves the wear resistance of the tool, but the LCA results show its potential for sustainability. Consequently, it holds promise for advancing the sustainable processing of challenging materials.

Ericksen-Landau Modular Strain Energies for Reconstructive Phase Transformations in 2D Crystals

By using modular functions on the upper complex half-plane, we study a class of strain energies for crystalline materials whose global invariance originates from the full symmetry group of the underlying lattice. This follows Ericksen’s suggestion which aimed at extending the Landau-type theories to encompass the behavior of crystals undergoing structural phase transformation, with twinning, microstructure formation, and possibly associated plasticity effects. Here we investigate such Ericksen-Landau strain energies for the modelling of reconstructive transformations, focusing on the prototypical case of the square-hexagonal phase change in 2D crystals. We study the bifurcation and valley-floor network of these potentials, and use one in the simulation of a quasi-static shearing test. We observe typical effects associated with the micro-mechanics of phase transformation in crystals, in particular, the bursty progress of the structural phase change, characterized by intermittent stress-relaxation through microstructure formation, mediated, in this reconstructive case, by defect nucleation and movement in the lattice.

In situ characterization of Ni-rich NMC811 thin films prepared by sol-gel method using different scanning probe microscopy techniques

In this paper, LiNi0.8Co0.1Mn0.1O2 (NMC811) thin films were prepared by the sol-gel method based on different parameter conditions, and the microstructure and electrochemical properties of the films were compared to obtain the film sample under the best preparation parameters. In order to explain the formation mechanism of cell battery performance based on the NMC811 cathode at the nano scale, electrochemical strain microscopy, conductive atomic force microscopy and Kelvin probe force microscopy are specifically utilized to study the changes of NMC811 thin film in electrochemical deformation, conductivity, and potential distribution under different electrical and thermal fields. The results indicate that the local amplitude, conductivity, and electrical potential of thin film in the scanning region increases with the voltage from 0 V to 3 V and the temperature from 25 °C to 150 °C. However, the electrochemical deformation, conductivity, and potential of the film decrease significantly when the voltage is applied to 4 V or the temperature rises to 200 °C.These results provide visual evidence for the influence of external field on the phase structure change and lithium-ion diffusion behavior of NMC811 thin film.

(AlCrNiTiZr)Nx high-entropy nitride coatings with enhanced hardness via tailoring N2 flow rates for anti-wear applications

(AlCrNiTiZr)Nx high-entropy nitride coatings with enhanced hardness are prepared by reactive magnetron cosputtering. The chemical composition, microstructure, as well as mechanical and tribological properties of the coatings are studied systematically. With N2 flow rates from 0 to 16 SCCM, the nitrogen content of the coatings increases to 55.7 at. % and the phase structure changes from amorphous to face-centered cubic. The hardness of the coating increases, obviously, with an increase in the nitrogen content. When the nitrogen flow rate is 12 SCCM, the coating has the highest hardness of 31.77 GPa and the lowest wear rate of 1.23 × 10−5 mm3/(N m) at room temperature. The wear resistance results show that all the hardness, adhesion strength, and damage tolerance contribute to the coating’s wear resistance.

Interannual Variability in the Boreal Summer Intraseasonal Oscillation Modulates the Meridional Migration of Western North Pacific Tropical Cyclone Genesis

Abstract Prior studies have emphasized the influence of the boreal summer intraseasonal oscillation (BSISO) on basin-scale and global-scale tropical cyclones (TCs). An improved understanding of the BSISO’s impact on TCs at various climate time scales will likely lead to improved subseasonal-to-seasonal prediction. This study explores the impact of BSISO interannual variability on western North Pacific (WNP) TCs. We find that interannual meridional variability in the BSISO modulates the meridional migration of WNP TC genesis and is related to changes in BSISO phase structure. These structural changes are characterized by occurrence frequency changes for individual BSISO phases between the equatorial region over the eastern Indian Ocean (EIO)–Maritime Continent (MC) and the subtropical region over the South China Sea (SCS)–western Pacific. This interannual north–south change of the BSISO appears to be associated with changes in sea surface temperature over the MC region and WNP mid-to-low-tropospheric moisture advection, mainly via remote forcing of a Gill-type Rossby response to BSISO convection and a large meridional asymmetry of the low-level background moisture distribution. During years with increased BSISO residence time over the subtropical SCS–western Pacific, more TCs occur over the northern WNP due to TC-favorable BSISO-associated convection and circulation. In contrast, more TCs occur over the southern WNP in years with increased BSISO convection residence time over the equatorial EIO–MC. We find that the increase in frequency of BSISO phase occurrence over the subtropical SCS–western Pacific since the late 1990s has potentially contributed to a recent poleward shift of WNP TC genesis.

Synthesis, structural, morphological and optical properties of environment friendly yellow inorganic pigment Bi4Zr3O12

This study reports on the structural, morphological, microstructural, electronic and optical properties of 5 nm (annealed at 300 °C) and 8 nm (annealed at 500 °C) sized nanocrystals of yellow inorganic pigment Bi4Zr3O12 prepared by sol-gel auto-combustion technique. Increase in the annealing temperature from 300 °C to 500 °C does not led to structural phase change but results in minor shifts in the 2θ position of Bragg peaks towards the higher angle side, which is attributed to reduction in the unit cell volume due to well crystallization. Phase pure formation and well crystallization of 8 nm sized Bi4Zr3O12 pigment in the fluorite type fcc symmetry in the space group Fm3‾m (No. 225) have been revealed first time by detailed Rietveld profile refinement of the X-ray diffractogram, FTIR, SAED and HRTEM analysis. The FESEM micrographs showed micro-flower type morphology of the rod shaped nanocrystals of the Bi4Zr3O12 pigments. EDS and XPS analysis confirmed the stoichiometry of the constituent elements present in the Bi4Zr3O12 pigments. XPS analysis evaluated +3, +4 and −2 oxidation states of the Bi, Zr and oxygen ions respectively and also rule out presence of organic species in the two pigments. ESR, Fluorescence and XPS analysis affirmed formation of oxygen vacancies in the two pigments. UV–Vis–NIR optical reflectance data showed marginal increment in the optical band gap upon raising the annealing temperature but 8 nm sized Bi4Zr3O12 nanocrystals have shown greater reflectance in comparison to 5 nm sized Bi4Zr3O12 nanocrystals. The photoluminescence spectroscopic analysis and CIE coordinates along with CCT values showed that yellow Bi4Zr3O12 pigment could be useful for optical devices and yellow pigment applications.

Topotactic Transition: A Promising Opportunity for Creating New Oxides

AbstractTopotactic transition is a structural phase change in a matrix crystal lattice mediated by the ordered loss/gain and rearrangement of atoms, leading to unusual coordination environments and metal atoms with rare valent states. As early as in 1990s, low temperature hydride reduction is utilized to realize the topotactic transition. Since then, topological transformations are developed via multiple approaches. Especially, the recent discovery of the Ni‐based superconductivity in infinite‐layer nickelates has greatly boosted the topotactic transition mean to synthesizing new oxides for exploring exotic functional properties. In this review, a detailed and generalized introduction is provided to oxygen‐related topotactic transition. The main body of the review includes four parts: the structure‐facilitated effects, the mechanism of the topotactic transition, some examples of topotactic transition methods adopted in different metal oxides (V, Mn, Fe, Co, Ni) and the related applications. This study is to provide timely and thorough strategies to successfully realize topotactic transitions for researchers who are eager to create new oxide phases or new oxide materials with desired functions.

Near-90° Switch in the Polar Axis of Dion-Jacobson Perovskites by Halide Substitution.

Ferroelectricity in two-dimensional hybrid (2D) organic-inorganic perovskites (HOIPs) can be engineered by tuning the chemical composition of the organic or inorganic components to lower the structural symmetry and order-disorder phase change. Less efforts are made toward understanding how the direction of the polar axis is affected by the chemical structure, which directly impacts the anisotropic charge order and nonlinear optical response. To date, the reported ferroelectric 2D Dion-Jacobson (DJ) [PbI4]2- perovskites exhibit exclusively out-of-plane polarization. Here, we discover that the polar axis in ferroelectric 2D Dion-Jacobson (DJ) perovskites can be tuned from the out-of-plane (OOP) to the in-plane (IP) direction by substituting the iodide with bromide in the lead halide layer. The spatial symmetry of the nonlinear optical response in bromide and iodide DJ perovskites was probed by polarized second harmonic generation (SHG). Density functional theory calculations revealed that the switching of the polar axis, synonymous with the change in the orientation of the sum of the dipole moments (DMs) of organic cations, is caused by the conformation change of organic cations induced by halide substitution.

Surface Energies of LaMnO3 High-Index Surfaces Obtained from Density-Functional Theory

The first six cubic LaMnO3 high-index surfaces, (210), (211), (221), (310), (311), and (320), are examined for the first time. The unrelaxed and relaxed surface energies of the surfaces are computed as a function of surface model thickness using unrelaxed and relaxed surface models, respectively. The (210), (320), (211), and (221) surfaces are found to be more stable than the low-index (011) and (111) surfaces. Helping to explain this result, the surface terminations of the (210), (320), (211), or (221) surface are seen to exhibit a rotational relaxation of the MnO6 or oxygen octahedra extending from the surface into the bulk. By contrast, the relaxed surface energies of the (310) and (311) surfaces are concluded to be difficult to determine due to a structural transformation or phase change in the surface models of the surfaces away from cubic LaMnO3. The finding of a phase change is important. It indicates that a phase change in the surface models of a surface for another material could occur if the surface is relatively open and a different phase of the material is stable at low temperature. When modeling such a surface, two steps are suggested to be taken.

Investigation of ion transport properties in Er–W co-doped La2Mo2O9 electrolytes

Here we present the structural, vibrational, dielectric as well as ionic transport properties in a series of La2-xErxMo1.7W0·3O9 (for 0 ≤ x ≤ 0.5). Stabilization of cubic β-phase at room temperature was achieved by doping, evident from XRD and conductivity plots. Raman analysis suggests a change in phase structure and deformation in Mo-polyhedra due to doping. Ionic conductivity of 10 mol% Er-doped sample was found to be 3.6 × 10−2 S/cm similar to that of pure La2Mo2O9 at 700 °C. Two different conduction mechanisms prevail: Arrhenius type below 450 °C and Vogel-Tammann-Fulcher (VTF) type above 450 °C. Dielectric constant and loss studies indicate the presence of two dielectric relaxations in the co-doped samples with different relaxation times attributed to the short-range diffusion of oxygen ions between different sites, i.e., O (1) ↔ O (2) and O (1) ↔ O (3). Electric modulus studies suggests that the relaxation mechanism is independent of temperature and composition.

Coexistent VO2 (M) and VO2 (B) Polymorphous Thin Films with Multiphase-Driven Insulator-Metal Transition.

Reversible insulator-metal transition (IMT) and structure phase change in vanadium dioxide (VO2) remain vital and challenging with complex polymorphs. It is always essential to understand the polymorphs that coexist in desired VO2 materials and their IMT behaviors. Different electrical properties and lattice alignments in VO2 (M) and VO2 (B) phases have enabled the creation of versatile functional devices. Here, we present polymorphous VO2 thin films with coexistent VO2 (M) and VO2 (B) phases and phase-dependent IMT behaviors. The presence of VO2 (B) phases may induce lattice distortions in VO2 (M). The plane spacing of (011)M in the VO2 (M) phase becomes widened, and the V-V and V-O vibrations shift when more VO2 (B) phase exists in the VO2 (M) matrix. Significantly, the coexisting VO2 (B) phases promote the IMT temperature of the polymorphous VO2 thin films. We expect that such coexistent polymorphs and IMT variations would help us to understand the microstructures and IMT in the desired VO2 materials and contribute to advanced electronic transistors and optoelectronic devices.

Activated carbon incorporated graphene oxide with SnO2 and TiO2-Zn nanocomposite for supercapacitor application

In this work, we have reported maximum specific capacity of novel activated carbon/graphene oxide/tin oxide (AC/GO/SnO2) and activated carbon/graphene oxide/titanium-zinc acetate dehydrate (AC/GO/TiO2-Zn) nanocomposites was synthesized by using hydrothermal method. The characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Ultraviolet-visible (UV-Vis.) absorption spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HR-TEM) were used to confirm the structural phase change, morphology, and microstructural arrangement in the AC/GO/SnO2 and AC/GO/TiO2-Zn nanocomposite. The symmetry supercapacitor electrode device was fabricated using the configuration of AC/GO/SnO2 and AC/GO/TiO2-Zn nanocomposite. The electrochemical properties of the fabricated nanocomposite electrodes and the fabricated supercapacitor was characterized using cyclic voltammetry (CV), galvanostatic charging-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques with 3 M KOH gel electrolytes. The AC/GO/TiO2-Zn electrode showed a maximum specific capacity of 1491.6 Fg−1 at a current density of 2.5 Ag−1 and a cycle stability of the capacity retention of 61.80 % even after 10,000 cycles. This result shows that the AC/GO/TiO2-Zn is an electrode material with good electrochemical reversibility and cycle stability for supercapacitor applications.

Radio Wave-Activated Chemotherapy-A Novel Nanoparticle Thermoresponsive Copolymer Drug Delivery Platform.

Radio waves are highly penetrating, non-ionizing, and cause minimal damage to surrounding tissues. Radio wave control of drug release has been achieved using a novel thermoresponsive copolymer bound to a superparamagnetic iron oxide nanoparticle (SPION) core. A NIPAM-acrylamide-methacrolein copolymer underwent a coil-to-globular structure phase change upon reaching a critical temperature above the human body temperature but below hyperthermic temperatures. The copolymer was covalently bound to SPIONs which increase in temperature upon exposure to radio waves. This effect could be controlled by varying input energies and frequencies. For controlled drug release, proteins were bound via aldehyde groups on the copolymer and amine groups on the protein. The radio wave-induced heating of the complex thereby released the drug-bearing proteins. The fine-tuning of the radio wave exposure allowed multiple cycles of protein-drug release. The fluorescent tagging of the complex by FITC was also achieved in situ, allowing the tagging of the complex. The localization of the complex could also be achieved in vitro under a permanent magnetic field.

Tailoring high-energy storage NaNbO3-based materials from antiferroelectric to relaxor states

Reversible field-induced phase transitions define antiferroelectric perovskite oxides and lay the foundation for high-energy storage density materials, required for future green technologies. However, promising new antiferroelectrics are hampered by transition´s irreversibility and low electrical resistivity. Here, we demonstrate an approach to overcome these problems by adjusting the local structure and defect chemistry, delivering NaNbO3-based antiferroelectrics with well-defined double polarization loops. The attending reversible phase transition and structural changes at different length scales are probed by in situ high-energy X-ray diffraction, total scattering, transmission electron microcopy, and nuclear magnetic resonance spectroscopy. We show that the energy-storage density of the antiferroelectric compositions can be increased by an order of magnitude, while increasing the chemical disorder transforms the material to a relaxor state with a high energy efficiency of 90%. The results provide guidelines for efficient design of (anti-)ferroelectrics and open the way for the development of new material systems for a sustainable future.

Random networks of disconnected nanoparticles in dielectric layers as a source of electric responsivity

Many efforts are currently focused on materials with responsive features for neural-inspired devices. Different approaches are followed, based on various mechanisms – from ferroelectric switching to structural phase changes, from magnetic tunnel junctions to metal filament formation. Here we analyze an alternative strategy based on an unconventional electrical response arising from percolative charge transport and charge trapping in discrete random networks of oxide nanostructures in a dielectric matrix. After an analysis of the mechanisms which can potentially be a source of a plastic response in this class of systems, we report evidence of this behavior in a system comprising an alkali-germanosilicate amorphous matrix with incorporated Ga-oxide nanostructures. The active material – consisting in a film 70 nm thick interfaced to p-type Si and Au electrodes – gives a responsive behavior to pulsed bias which is accompanied by bias dependent electric conduction, with resistivity changes of an order of magnitude by applying 2 V, as well as a dielectric response with hysteretic features, as expected by the model. The results represent a first proof of concept of an unexplored strategy for the design of responsive systems.

Tuning superconductivity and charge density wave order in TaSe2 through Pt intercalation

Tantalum diselenide ($\mathrm{Ta}{\mathrm{Se}}_{2}$) has emerged as a promising platform to investigate the interplay between two intriguing quantum electronic states in materials: the charge density wave order (CDW) and superconductivity. In this work, we report the ability to tune these quantum electronic states by intercalating Pt into $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$. By introducing 20% of Pt into $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$, we demonstrate that the structural phase changes from the $2H$ to the $4{H}_{b}$ phase of $\mathrm{Ta}{\mathrm{Se}}_{2}$ with Pt atoms intercalated within the van der Waals spacing. According to the Fermi surface of the $4{H}_{b}$ phase, a Lifshitz transition occurred, destroying the Fermi-surface nesting found in the $2H$ phase. This can be attributed to the structural phase transformation and the influence of donated electrons from Pt, thus tuning the Van Hove singularities into the Fermi-level vicinity, suppressing the CDW state, and enhancing the superconducting temperature $({T}_{c})$ to $\ensuremath{\sim}2.7$ K. The resulting superconducting properties of the $4{H}_{b}\ensuremath{-}\mathrm{P}{\mathrm{t}}_{0.2}\mathrm{Ta}{\mathrm{Se}}_{2}$ are consistent with those of a BCS type-II superconductor, with a superconducting gap of 3.0 meV. Our results provide insights into the role of electron doping and structural phase changes in fine-tuning quantum electronic-state phenomena in materials. These findings could have significant implications in designing superconducting materials with tailored properties for practical applications.