Types Of Phase Boundaries Research Articles

Modeling the phase boundaries in Cu(100)-(2√2 × √2)R45°-O missing row reconstruction (MRR) structure

Although the structure of Cu(100)-(22×2)R45°-O missing row reconstruction (MRR) has been well-established for decades, the detailed structure of its various boundaries remains an untilled area due to the difficulties in obtaining atomically resolved images. Herein, atomic arrangement of the phase boundaries existing in MRR structure was modeled on the basis of scanning tunneling microscopy (STM) investigations. By determining the periodicity and unit structure of MRR in STM images and extending them to boundary region, several types of phase boundaries were identified, resulted respectively from: (1) the mismatch between c(2 × 2)-O patches, (2) the regulation by step edges, and (3) the mismatch between Cu missing rows (MRs). With the modeled structure, it was revealed that the types of the c(2 × 2)-O mismatch induced phase boundaries (OMIPBs) are mainly dominated by the oxygen exposure and in-diffusion barrier. The step edge regulated phase boundaries (SERPBs) are always terminated with Cu-O chain and may represent an intermediate growth stage to larger MRR structure. Comparatively, Cu MRs mismatch is often reconciled by the differently oriented domains between them. As a result, the Cu MRs mismatch induced phase boundaries (CMRMIPBs) are only occasionally observed as Cu-O chains between mismatched Cu MRs that encounter shoulder-to-shoulder. For all studied boundaries, the surrounding MRR domains exhibit obvious orientation preference through inclined packing along the SP direction with the degree closely related with the width of the boundaries.

Exotic magnetization curves in classical square-kagomé spin lattices

Classical spin systems with non-coplanar ground states typically exhibit nonlinear magnetization curves characterized by kinks and jumps. Our article briefly summarizes the most important related analytical results. In a comprehensive case study, we then address AF-square kagomé and AF/FM-square kagomé spin lattices equipped with additional cross-plaquette interactions. It is known that these systems have non-coplanar ground states that assume a cuboctahedral structure in the absence of a magnetic field. When a magnetic field H is switched on, a rich variety of different phases develops from the cuboctahedral ground state, which are studied in their dependence on H and a cross-plaquette coupling constant J3>0 . For the AF square-kagomé spin lattice, we carefully identify and describe seven phases that appear in a phase diagram with five triple points. The transitions between these phases are predominantly discontinuous, although two cases exhibit continuous transitions. In contrast, the phase diagram of the AF/FM square-kagomé model shows only four phases with a single triple point, but these also lead to exotic magnetization curves. Here, too, there are two types of phase boundaries belonging to continuous and discontinuous transitions.

Topological nonmediocre nodes on two-leg superconducting quantum circuits

Topological gapless systems, as the connection of the different topological quantum phases, have received much attention. Topological nonmediocre nodes are typically observed in two- or three-dimensional gapless systems. In this paper, we demonstrate that the topological nonmediocre nodes are existent in a model that lies between one dimension and two dimensions. Superconducting circuits, as essential all-solid state quantum devices, have offered a promising platform for studying the macro-controlling quantum effects. Recently, experimental achievements have enabled the realization of tunable coupling strengths between transmon qubits and the implementation of a one-dimensional Su-Schrieffer-Heeger (SSH) model [Li X <i>et al.</i> <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1103/PhysRevApplied.10.054009">2018 <i>Phys. Rev. Appl.</i> <b>10</b> 054009</ext-link>]. According to this work, herein we present a two-leg SSH model implemented in superconducting circuits and demonstrate the existence of topological nonmediocre nodes. Firstly, two-leg superconducting circuit with transmon qubits which are coupled with their nearest-neighbor sites by capacitors is designed. To construct the two-leg SSH model, we introduce two alternating-current magnetic fluxes to drive each transmon qubit. We discover two types of phase boundaries in the SSH model and obtain the corresponding energy spectra and phase diagram. We identify two distinct topological insulating phases characterized by winding number ±1, and the corresponding edge states exhibit distinct characteristics. Moreover, we discuss the topological properties of the two phase boundaries. By representing the Bloch states as a vector field in <i>k</i> space, we demonstrate the existence of two kinks of nonmediocre nodes with first-type phase boundaries. These two nonmediocrenodes possess distinct topological charges of 1 and –1, respectively. On the other hand, the nonmediocre nodes with the second-type phase boundaries are topologically trivial. These results open the way for exploring novel topological states, ladder physical systems, and nodal point topological semimetals.

Irradiation-induced corrosion tendencies evolution at the phase boundaries containing carbides in duplex stainless steel

Irradiation-assisted stress corrosion cracking normally initiates and propagates along grain/phase boundaries. Here, by using scanning Kelvin probe force microscopy, we characterized the Volta potential difference (VPD) changes prior and after proton irradiation at austenite/carbide (γ/C), ferrite/carbide (δ/C) and austenite/ferrite (γ/δ) interfaces in a 308 L stainless steel. It was found that, prior to irradiation, γ/C boundary had the lowest VPD, followed by δ/C and γ/δ. VPDs of all three types of phase boundaries slightly decreased after proton irradiation, wherein the γ/C boundary showed the largest VPD drop, followed by δ/C and γ/δ. The γ/C interface demonstrates the highest tendency of corrosion.

Proposal of a rhombohedral-tetragonal phase composition for maximizing piezoelectricity of (K,Na)NbO3 ceramics

Great progress in the field of piezoelectricity of (K,Na)NbO3 (KNN) lead-free ceramics, driven by emerging rhombohedral-tetragonal (R-T) phase boundary, has instigated research activity regarding elaborate controls of the phase boundary structure. Through phase-microstructure-property mapping in KNN ceramics doped with Bi-containing perovskite oxides, in this study we for the first time report the existence of a certain R-T phase boundary state by which to create maximum piezoelectric response in KNN systems. This phase boundary condition is usually comprised of approximately 15% R phase and 85% T phase, regardless of the choice of dopant material. Any deviation from this phase composition, either by inclusion of orthorhombic (O) phase or by enrichment of R phase, has a negative effect on the value of d33. These findings can provide useful guidance for chemical doping control associated with the type of phase boundary and the phase composition for advanced KNN-based materials.

The phase structure and dielectric properties around a new type of phase boundary in a lead ytterbium niobite based solid solution.

The phase boundaries of dielectric materials have constantly been valuable for instructing the design of phase structures, revealing correlations between compositions and structures, and attaining the desired functional properties for piezoelectric, pyroelectric, electrostriction, electrocaloric, energy storage and energy harvesting applications. We here observe a new type of phase boundary in a solid solution of xPbTiO3·(1 - x)Pb(Yb1/2Nb1/2)O3 (x = 0.00-0.20), which is between an antiferroelectric (AFE) phase and a relaxor ferroelectric (RFE) phase. x = 0.10 is confirmed as the phase boundary. XRD, TEM, PFM and Raman spectroscopy analysis reveal two fundamental traits of the phase structure: (1) the polar state changes from AFE to FE order; and (2) the domain range evolves from micrometer-sized to nanometer-sized, both of which are normally separated but coexist around the phase boundary. The intriguing phase structure contributes to the distinctive dielectric properties: (1) a broad compositional zone (x < 0.10 and x ≥ 0.14) features low remnant polarization, low hysteresis and highly reversible domain wall motion, and is expected to be utilized for dielectric energy storage and electrostriction applications; and (2) a narrow nonergodic RFE zone (0.10 ≤ x < 0.14) demonstrates remnant and maximum polarization, co-dominated by composition and temperature, and has potential for pyroelectric and electrocaloric applications.

Stable 1T Tungsten Disulfide Monolayer and Its Junctions: Growth and Atomic Structures.

Transition-metal dichalcogenides in the 1T phase have been a subject of increasing interest, which is partly due to their fascinating physical properties and partly to their potential applications in the next generation of electronic devices, including supercapacitors, electrocatalytic hydrogen evolution, and phase-transition memories. The primary method for obtaining 1T WS2 or MoS2 has been using ion intercalation in combination with solution-based exfoliation. The resulting flakes are small in size and tend to aggregate upon deposition, forming an intercalant-TMD complex with small 1T and 1T' patches embedded in the 2H matrix. Existing growth methods have, however, produced WS2 or MoS2 solely in the 2H phase. Here, we have refined the growth approach to obtain monolayer 1T WS2 up to 80 μm in size based on chemical vapor deposition. With the aid of synergistic catalysts (iron oxide and sodium chloride), 1T WS2 can nucleate in the infant stage of the growth, forming special butterfly-like single crystals with the 1T phase in one wing and the 2H phase in the other. Distinctive types of phase boundaries are discovered at the 1T-2H interface. The 1T structure thus grown is thermodynamically stable over time and even persists at a high temperature above 800 °C, allowing for a stepwise edge epitaxy of lateral 1T heterostructures. Atomic images show that the 1T WS2-MoS2 heterojunction features a coherent and defectless interface with a sharp atomic transition. The stable 1T phase represents a missing piece of the puzzle in the research of atomic thin van der Waals crystals, and our growth approach provides an accessible way of filling this gap.

Progress on the doping and phase boundary design of potassium–sodium niobate lead-free ceramics

Potassium–sodium niobate (K,Na)NbO3/(KNN) lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones. In recent years, the author’s group concentrated their work on KNN-based ceramics. This paper reviews the main obtained results in authors’ laboratory on how to enhance the piezoelectric properties of KNN-based ceramics, including the ions or compounds substitution, the constructing and types of phase boundaries near room temperature, the investigation of other tools (sintering aids, synthesis technique, poling conditions) on properties. All the published papers up to now show the developing higher performance with maintaining high Curie temperature of KNN-based ceramics which has great potential for the future and is the key to success for the field.

Influence of the Type of Phase Boundary on the Deformation Behavior and Evolution of a Defect Subsystem of Heterophase Alloys with FCC Matrix, Strengthened by Micro- and Nanoparticles

A mathematical model of plastic deformation of dispersion-hardened materials with FCC matrix and strengthening particles having various coupling with the matrix is presented. The model is based on the equations of balance of strain-induced defects of various types with allowance for their transformation in the process of plastic deformation. The influence of scale characteristics of the strengthening phase, temperature, and strain rate on the evolution of the dislocation subsystem and on strain hardening of an alloy with FCC matrix is investigated. Strain hardening is observed in materials with nanosized strengthening phase that is more intense than in materials with larger particles, independent of phase coupling with the matrix, for the same volume fraction of the strengthening phase.

New lead-free piezoelectric ceramics based on (K0.48Na0.52)(Nb0.95Ta0.05)O3–Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3

(1 - x)(K0.48Na0.52)(Nb0.95Ta0.05)O3-xBi0.5(Na0.7K0.2Li0.1)0.5ZrO3 lead-free piezoelectric ceramics with a new type of phase boundary have been designed and fabricated. This phase boundary lies in the compositional range of 0.04 ≤ x ≤ 0.05, and is formed by the coexistence of the rhombohedral, orthorhombic, and tetragonal phases. Interestingly, we found that the ferroelectric, dielectric, and piezoelectric properties of the ceramics with compositions near the phase boundary are significantly enhanced. In particular, the ceramic with x = 0.045 shows the best piezoelectric behavior of d33 ∼ 290 pC/N and kp ∼ 0.42 among all the compositions studied in this work, and it also exhibits a good thermal stability at annealing temperatures of ≤270 °C. All these results indicate that such a material system is a good candidate for lead-free piezoelectric applications in the future.

Evolution of incommensurate spin order with magnetic field and temperature in the itinerant antiferromagnet GdSi

GdSi exhibits spin-density-wave (SDW) order arising from the cooperative interplay of sizeable local moments and a partially nested Fermi sea of itinerant electrons. Using magnetotransport, magnetization, and nonresonant magnetic x-ray diffraction techniques, we determine the H-T phase diagrams of GdSi for magnetic fields up to 21 T, where antiferromagnetic order is no longer stable, and field directions along each of the three major crystal axes. While the incommensurate magnetic ordering vector that characterizes the SDW is robust under magnetic field, the multiple spin structures of this compound are highly flexible and rotate relative to the applied field via either canting or spin-flop processes. The antiferromagnetic spin densities always arrange themselves transverse to the applied magnetic field direction. The phase diagrams are delineated by two types of phase boundaries: one separates a collinear from a planar spin structure associated with a lattice structural transition, and the other defines a spin flop transition that is only weakly temperature dependent. The major features of the phase diagrams along each of the crystal axes can be explained by the combination of local moment and global Fermi surface physics at play.

Tracking multi-phase boundaries using an integration-based approach

An integration-based method to track multi-phase boundaries for multi-component alloys systems is proposed. The foundation of the method is considering the phase boundary tracking as an initial value problem. It starts with the utilization of Gibbs–Duhem relation to find the slope of a phase boundary (the partial derivatives of the solvus temperature with respect to the equilibrium phase composition) and the partial derivatives of partition coefficients with respect to the equilibrium phase composition. Then, with these derivatives and a pair of known initial points on a phase boundary, the rest of the phase boundary can be calculated using a numerical integration technique such as the Runge–Kutta or Predictor–Corrector method in a stepwise manner. The integration method has been applied to track various types of phase boundaries in binary, ternary and quaternary systems. The calculated ones are in good agreement with the ones obtained by the commercial CALPHAD software Thermo-Calc. It provides a different computational method for the tracking of multi-phase boundaries and might be useful in the calculation of phase diagram when combined with the overlapping of Zero Phase Fraction (ZPF) lines technique and global minimization technique.

Coarsening dynamics of the convective Cahn-Hilliard equation

We characterize the coarsening dynamics associated with a convective Cahn-Hilliard equation (cCH) in one space dimension. First, we derive a sharp-interface theory through a matched asymptotic analysis. Two types of phase boundaries (kink and anti-kink) arise, due to the presence of convection, and their motions are governed to leading order by a nearest-neighbors interaction coarsening dynamical system ( CDS ). Theoretical predictions on CDS include: • The characteristic length L M for coarsening exhibits the temporal power law scaling t 1/2; provided L M is appropriately small with respect to the Peclet length scale L P . • Binary coalescence of phase boundaries is impossible. • Ternary coalescence only occurs through the kink-ternary interaction; two kinks meet an anti-kink resulting in a kink. Direct numerical simulations performed on both CDS and cCH confirm each of these predictions. A linear stability analysis of CDS identifies a pinching mechanism as the dominant instability, which in turn leads to kink-ternaries. We propose a self-similar period-doubling pinch ansatz as a model for the coarsening process, from which an analytical coarsening law for the characteristic length scale L M emerges. It predicts both the scaling constant c of the t 1/2 regime, i.e. L M =ct 1/2 , as well as the crossover to logarithmically slow coarsening as L M crosses L P . Our analytical coarsening law stands in good qualitative agreement with large-scale numerical simulations that have been performed on cCH.

Control of phase separation behavior of PC/PMMA blends and their application to the gas separation membranes

Gas transport and thermodynamic properties for the blends of polycarbonate (PC) and polymethylmethacrylate (PMMA) were studied. To explore glass transition temperatures of blends and their phase separation temperatures due to a lower critical solution temperature, LCST, a type of phase boundary, transparent blend films that are miscible and do not contain solvent-induced PC crystals were prepared by controlling molecular weights of each component. The average value of interaction energy densities between PC and PMMA obtained from the phase boundaries and the equation of a state theory based on the lattice fluid model was 0.04 cal/cm3. This result confirmed that miscibility of PC and PMMA blends at equilibrium depends upon the molecular weights of components. Gas transport properties of miscible blends and immiscible blends having the same chemical components and composition but a difference in morphology were examined at 35°C and 1 atm for the gases N2 and O2. Permeability and apparent diffusion coefficients were ranked in the order of the immiscible blend having a domain–matrix structure > the immiscible blend having an interconnected structure > the miscible blend. These results might be related to the differences in the local chain motions that depend on the intermolecular mixing level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2950–2959, 1999

Spinodal decomposition and succeeding crystallization in PCL/SAN blends

For a binary blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5wt% of acrylonitrile, the lower critical solution temperature (LCST) type of phase boundary was determined by thermo-optical analysis. A critical mixture, 80/20 PCL/SAN blend, initially underwent spinodal decomposition (SD) above the LCST and then crystallized at a lower temperature (40°C). Isothermal crystallization was analyzed by differential scanning calorimetry. The longer the SD duration the higher the rate of crystallization. An optimum SD time yielding the highest degree of crystallization was found to exist at a relatively early stage of SD (ca. 5min). The blend via the optimum time of SD showed the highest melting point. In the blend, a very long and straight crystal lamella was observed by transmission electron microscopy. Thus, the effect of the degree of demixing on the succeeding crystallization was revealed.

Microstructural changes during superplastic deformation of powder-consolidated nickel-base superalloy IN–100

Changes in the microstructure occurring during superplastic deformation of the powder-consolidated nickel-base superalloy IN–100 at 1311 K are reported. The initial microstructure was shown to contain a range of recovered and recrystallized grains together with some warm-worked unrecrystallized grains of high dislocation density. Heating to the test temperature and holding produced no changes in microstructure other than dissolution of M23C6 precipitates. Prolonged annealing at the test temperature without deformation led principally both to a reduction in the volume fraction of warm-worked areas and removal of some dislocations from recrystallized grains. Deformation in the high strainrate regime (region III) produced grain refinement associated with a marked increase in dislocation density and some cavitation. Some randomization of the distribution of MC carbides on the prior particle boundaries occurred which implied that substantial grain-boundary sliding had taken place. In the regime of optimal superplasticity (region II) structural modification occurred gradually. After deformation at the lowest strain rates (region I) a reduction in dislocation density was again observed with most grains dislocation free. Extensive dislocation activity was noted at all types of phase boundaries during deformation in regions I and II. From the observations it is concluded that deformation in regions I and II takes place by grain-boundary sliding with accommodation by both slip and diffusion with the diffusional component increasing as the strain rate decreases.

Representation of different types of phase boundaries

Representation of different types of phase boundaries