Coexistence Of Multiple Phases Research Articles

Bonding states underpinning structural transitions in IrTe2 observed with micro-ARPES

Competing interactions in low-dimensional materials can produce nearly degenerate electronic and structural phases. We investigate structural phase transitions in layered IrTe2 for which a number of potential transition mechanisms have been postulated. The spatial coexistence of multiple phases on the micron scale has prevented a detailed analysis of the electronic structure. By exploiting micro-angle-resolved photoemission spectroscopy obtained with synchrotron radiation we extract the electronic structure of the multiple structural phases in IrTe2 in order to address the mechanism underlying the phase transitions. We find direct evidence of lowered energy states that appear in the low-temperature phases, states previously predicted by calculations and extended here. Our results validate a proposed scenario of bonding and antibonding states as the driver of the phase transitions. Published by the American Physical Society 2024

Three‐Dimensional Imaging of the Structural Phase Transition in a Single Vanadium Dioxide Nanocrystal

Vanadium dioxide (VO2) is a strongly correlated material that exhibits a number of structural phase transitions (SPT) near to room temperature of considerable utility for various technological applications. When reduced to the nanoscale, a foreknowledge of surface and interface properties of VO2 during the SPT can facilitate the development of devices based on VO2. Herein, it is shown that Bragg coherent X‐ray diffractive imaging (BCDI) combined with machine learning is an effective means to recover three‐dimensional images of a single VO2 nanocrystal during a temperature‐induced SPT from a room‐temperature monoclinic phase to a high‐temperature rutile phase. The findings reveal the coexistence of multiple phases within the nanocrystal throughout the transition, along with missing density which indicates the presence of a newly formed rutile phase.

Design of shape memory alloys with low hysteresis via multiple phase coexistence

Shape memory alloys (SMAs) are the key components of actuators and sensors due to their shape memory effect and superelasticity. However, the thermal hysteresis associated with martensitic phase transformation limits their use in the long-duration precise control. We report a strategy that obtains SMAs with low hysteresis by constructing a composition-temperature pseudo phase diagram. This strategy is inspired by the physically parallel ferroelectric system where the hysteresis is minimized at the multiple phase coexistence point, due to the absence of energy barrier across different phases. Following this, an alloy in the phase diagram with a low hysteresis of about 5 K is synthesized. In contrast, those alloys compositionally different from the optimal one have large hysteresis. Microstructures characterization and diffraction analysis are employed to identify the multiple phase coexistence. The proposed strategy should be general and can shed light on the rational design of SMAs with low hysteresis.

KBiFe2O5 triggered-phase transition of Bi2Fe4O9 and Fe3O4 in tellurite glass with huge nonlinear and magnetic properties

In the quest for glass materials with high nonlinearity and strong magnetism to meet the demands of advancing technology, magnetic nanocrystal (NC) doping emerges as a promising approach. The paper investigates the phase transition from KBiFe2O5 to Bi2Fe4O9 and Fe3O4 NCs within a TeO2–Bi2O3–B2O3 glass matrix. The novelty of this study lies in leveraging the coexistence of multiple phases to amplify both the polarization and magnetic moment of glass. Various techniques, including X-ray diffraction, transition transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and vibrational sample magnetometer were employed to analyze the impact of NCs content and heat treatment temperature on crystallization, structure modification, and properties. KBiFe2O5 NCs doping induces changes in crystal phases and modifies the glass network structure by forming multi-valence states and altering coordination numbers, such as FeO4→FeO6, TeO4→TeO3, and BO4→BO3. Concurrently, appropriate temperature conditions result in reduced NC size, preserving glass transparency and thermal stability. Spinel Fe3O4 NCs formation at higher temperatures enhances magnetic behavior. A glass sample containing 1 mol% KBiFe2O5 NCs, heat-treated at 410 °C, exhibits a narrow bandgap (Eg) of 1.82 eV, high nonlinear parameters (α3 = 3.98 × 10−10 m/W, χ(3) = 8.65 × 10−11 esu), and a low limiting threshold (1.01 × 1012 W/m2). Additionally, owing to the incorporation of high spin states and active magnetic exchange interactions, the same glass demonstrates robust ferromagnetic behavior (Ms = 2.3 emu/g and Hc = 850 G). The approach developed in this study has been demonstrated to be highly effective in producing transparent glass with promising nonlinearity and magnetic performance suitable for photonics applications.

Tuning structural, dielectric, and ferroelectric properties of BTO-based ceramics through dual-site substitution

Different strategies for tuning the properties of ferroelectric materials have been employed for advancing electromechanical applications. Among several material synthesis techniques explored, site substitution is an effective approach. The present work focuses on Ba1-xCaxSnyTi1-yO3 (BCST) ceramics prepared by solid-state sintering route with different substitution levels (x = 0, 0.05 and y = 0, 0.09). The impact of site substitution on the properties of Barium Titanate (BTO), phase purity, structural analysis, chemical composition, dielectric, and ferroelectric properties have been studied. An ionic radii difference at A-site and B-site substitution is a key factor to achieve significant changes in physical and structural properties. X-ray diffraction patterns ensure the formation of pure phase perovskite structure in all the compositions. Raman spectroscopy indicates Ca substitution not only occurs at the A-site but also within the oxygen octahedra, adversely affecting the properties. Ca and Sn act as strong grain growth inhibitors, leading to a fine-grained and dense microstructure in BCST. While Ca substitution has a limited impact on the Curie temperature (TC), Sn substitution lowers TC in BST (54 °C) and BCST (50 °C) compared to BTO (126 °C). The Sn substitution results in the coexistence of multiple phases (rhombohedral, tetragonal and orthorhombic) in BST, enhancing its properties (ε' = 6118 at RT, Pr = 5.50 μC/cm2, Q11 = 0.060 m4/C2, d*33 = 526 pm/V) in comparison to BTO. These results acknowledge the role of substituents in lattice disruption, paving the way for chemistry-based materials design in the field of dielectric, actuator and energy storage applications.

DFT-based 11B solid-state NMR calculations for guiding fine local structure identification and phase-property modulation in ZnxY1-xBO3-0.5x borate oxide ion conductors.

Solid-state nuclear magnetic resonance (NMR) spectroscopy serves as a powerful technique for probing local structures. However, the interpretation of NMR signals mainly based on empirical knowledge could lead to imprecise local structural determinations. To address this, density functional theory (DFT)-based theoretical NMR calculations, aided by experimental three-dimensional continuous rotation electronic diffraction (3D cRED) technique, were performed for ZnxY1-xBO3-0.5x borate oxide ion conductors. The calculations provided fine local structure identification for the experimental 11B NMR spectra of ZnxY1-xBO3-0.5x, providing rich information on multiple experimental 11B NMR signals towards the complex boron oxide anions associated with bridging oxygen vacancies and the coexistence of the monoclinic (C2/c), hexagonal (P63/m), and trigonal (R32) phases in ZnxY1-xBO3-0.5x. Owing to the advantages of solid-state NMR in identifying closely related phases compared to X-ray/neutron diffraction technique, along with the advanced 3D cRED technique that allows for rapid phase identification and structure determination, we provide a fine local structure identification and a more inclusive insight into the coexistence of multiple phases in borate with the same composition. More importantly, this work provides guidance for phase and property modulation. Phase modulation in ZnxY1-xBO3-0.5x was carried out with thermodynamic and kinetic modulation and eventually realized the tuning of the local structures and the resultant oxide ion conductivity of ZnxY1-xBO3-0.5x. This work provides a theoretical and experimental platform to access the flexible structural assignment of boron oxide anions and therefore offers new guidance and insights into the defect structures and the phase-property modulation of inorganic solid functional materials beyond borate oxide ion conductors.

Multi‐Length Engineering of (K, Na)NbO3 Films for Lead‐Free Piezoelectric Acoustic Sensors with High Sensitivity

AbstractWith increasing concerns about noise pollution, the pursuit of highly dependable piezoelectric acoustic sensors for real‐time noise monitoring has come to the forefront of scientific research. Lead‐based perovskite piezoelectric films, exemplified by lead zirconate titanate Pb(Zr,Ti)O3 (PZT), surpass traditional piezoelectric materials such as ZnO and AlN in their piezoelectric properties, promising substantial advancements in next‐generation acoustic sensor technologies. However, the toxic nature of lead in PZT materials poses formidable environmental and human health risks. In an unprecedented breakthrough, it presents the pioneering development of an environmentally benign lead‐free piezoelectric Micro‐Electro‐Mechanical System (MEMS) acoustic sensor based on potassium sodium niobate (K,Na)NbO3 (KNN) film. High‐quality <001> textured 3 µm‐thick KNN film is successfully integrated into commercially used Si substrate, rendering exceptional piezoelectricity (transverse piezoelectric coefficients e31* of ≈8.5 C m−2) with satisfactory thermal stability. The atomic‐scale Z‐contrast imaging and piezoresponse force microscopy characterizations reveal that the outstanding piezoresponse originates from the local coexistence of multiple phases and the enhancement of extrinsic piezoelectric contributions from in‐plane polarization anisotropy. Finite element simulation is employed to design the triangular cantilever structure and annular diaphragm structure, each corresponding to different operating bandwidths. The resultant MEMS acoustic sensors stand out with outstanding acoustic performance (the high sensitivity and expansive receiving field of view), which are attributed to the microstructural engineering at multi‐length scales for the excellent piezoelectric properties of KNN film. These features enable sensitive acoustic monitoring in various environments, including large‐scale power grids and urban traffic.

Editorial: Multiphase flow in energy studies and applications—A special issue for MTCUE-2022

Establishing a clean, low-carbon, and efficient energy system is paramount for the sustainable development of industries and human society. Multiphase flows are encountered extensively in various energy applications, including transportation, conversion, and utilization of fossil, renewable, hydrogen, and nuclear energies. These flows encompass a wide range of phenomena, such as fluid flow, heat and mass transfer, combustion, and chemical reactions. However, multiphase flows are highly intricate due to the coexistence of multiple phases, states, and components, as well as the interactions among them that occur across diverse spatiotemporal scales. Consequently, both academia and industry face significant challenges in comprehending and harnessing multiphase flows. Thus, establishing connections between basic research and industrial applications in the field of multiphase flows is fundamental and indispensable for advancements in energy science and technologies.

Reversible Ultrathin PtOx Formation at the Buried Pt/YSZ(111) Interface Studied In Situ under Electrochemical Polarization.

Three different platinum oxides are observed by in situ X-ray diffraction during electrochemical potential cycles of platinum thin film model electrodes on yttria-stabilized zirconia (YSZ) at a temperature of 702 K in air. Scanning electron microscopy and atomic force microscopy performed before and after the in situ electrochemical X-ray experiments indicate that approximately 20% of the platinum electrode has locally delaminated from the substrate by forming pyramidlike blisters. The oxides and their locations are identified as (1) an ultrathin PtOx at the buried Pt/YSZ interface, which forms reversibly upon anodic polarization; (2) polycrystalline β-PtO2, which forms irreversibly upon anodic polarization on the inside of the blisters; and (3) an ultrathin α-PtO2 at the Pt/air interface, which forms by thermal oxidation and which does not depend on the electrochemical polarization. Thermodynamic and kinetic aspects are discussed to explain the coexistence of multiple phases at the same electrochemical conditions.

Mechanics Underpinning Phase Separation of Hydrogels.

This paper reveals the underpinning role of mechanical constraints and dynamic loading in triggering volume phase transitions and phase separation of hydrogels. Using the Flory-Rehner free energy that does not predict phase separation of hydrogels under equilibrium free swelling, we show that mechanical constraints can lead to coexistence of multiple phases. We systematically obtain the states of equilibrium for hydrogels under various mechanical constraints and unravel how mechanical constraints change the convexity of the free energy and monotonicity of the stress-stretch curves, leading to phase coexistence. Using a phase-field model, we predict the pattern evolution of phase coexistence and show that many features cannot be captured by the homogeneous states of equilibrium due to large mismatch stretch between the coexisting phases. We further reveal that the system size, quenching rate, and loading rate can significantly influence the phase behavior, which provides insights for experimental studies related to morphological patterns of hydrogels.

The origin of piezoelectric enhancement in compositionally graded ferroelectrics with sinusoidal variation

The direct piezoelectric effect of BaTiO3↔ Ba1−xSrxTiO3 graded ferroelectrics, whose compositions change in a sinusoidal form, is investigated via an extended phase-field method. The obtained results demonstrate that the piezoelectric coefficient can be significantly enhanced by controlling the amplitude of sinusoidal variation. The origin of piezoelectric enhancement is investigated by considering the formation of polarization domain structures and their behaviors under strain. Although a ferroelectric tetragonal phase or a paraelectric cubic phase primarily form in homogeneous Ba1−xSrxTiO3 ferroelectrics with a different content x, interestingly, an unusual ferroelectric monoclinic phase can be formed in compositionally graded ferroelectrics, giving rise to the coexistence of multiple phases. The monoclinic phase emerges as a result of the process that reduces built-in electric potential induced by a large gradient of polarization. In turn, the formation of the monoclinic phase gives rise to transient zones that make the polarization field more susceptible to external strains, thereby enhancing the piezoelectric response. We further demonstrate that the piezoelectric enhancement strongly depends on the volume fraction of the monoclinic phase in compositionally graded ferroelectrics, suggesting a route for the rational design of polarization domains and piezoelectric effects.

Probing ethane phase changes in bead pack via high-field NMR spectroscopy

Phase equilibria analysis in two-phase systems requires discernment of the individual phases as well as the interfacial region. The phase behavior of fluids in constraint geometries have been studied through several techniques. High-Field Nuclear Magnetic Resonance (HF-NMR) can be used to detect fluid phases, i.e. gas, liquid, or supercritical fluid, in the bulk or under confinement. In solution-state HF-NMR, each phase exhibits a distinct chemical shift that correlates to the phase density. In turn, the emergence of multimodal in NMR spectra reveals the coexistence of multiple phases in fluid systems. Our results for ethane show that HF-NMR can enable tracking phase changes in the bulk, but also in macro-scale (10–100′s μm in pore size) porous systems at various pressure and temperature conditions, even when the system us out of equilibrium. These results creates potential opportunities to investigate phase changes influenced by confinement in porous systems, though additional steps are necessary.

Stable Yellow Light-Emitting Diodes Based on Quasi-Two-Dimensional Perovskites.

Perovskite light-emitting diodes (PeLEDs) show great potential in display and lighting because of their tunable wavelength, narrow emission bandwidths, and high color purity. Currently, the external quantum efficiency (EQE) of red and green PeLEDs has reached >23%. However, yellow PeLEDs are still rarely reported because of phase separation in mixed-halide perovskites and the coexistence of multiple phases in quasi-two-dimensional (quasi-2D) perovskites L2An-1BnX3n+1 (n = 1, 2, 3, ...), where L is a bulky organoammonium ligand. Here, we fabricate stable yellow PeLEDs by manipulating the phase distribution and incorporating rubidium cations (Rb+) in quasi-2D perovskites. The transient absorption results confirm that alkylammonium ligand butyl ammonium (BA) has a narrower phase distribution than phenylethyl ammonium (PEA) in the quasi-2D perovskites, resulting in a more blue-shifted emission peak. We further incorporate a proper molar ratio of Rb+ in the (BA)2CsPb2I7 perovskite to blue-shift the emission peak to the yellow range. Finally, the yellow PeLEDs exhibit an EQE of 3.5%, and the stable emission peak is located at 595 nm. Our work provides a useful approach for the fabrication of highly efficient and stable yellow PeLEDs.

Thickness‐Driven Morphotropic Phase Transition in Metastable Ferroelectric CaTiO3 Films

AbstractThe intimate coexistence of multiple phases in ferroelectrics has been shown to result in exotic electromechanical properties, such as giant piezoelectricity. Here, via a thickness‐driven phase transition, the phase coexistence and enhanced piezoelectricity in a few tens of nanometers thick, Pb‐free CaTiO3 films are demonstrated. Due to the competition between interfacial and bulk energies, as film thickness increases, epitaxial CaTiO3 films exhibit a ferroelectric‐to‐paraelectric phase transition that is concomitant with the rhombohedral‐to‐orthorhombic structural transition. This so‐called thickness‐driven morphotropic phase transition (MPT) in nanoscale CaTiO3 films stems from the metastable nature of ferroelectricity. The resulting morphotropic phase boundary at the atomic scale in nanoscale CaTiO3 films is visualized. It is also shown that this thickness‐driven MPT can lead to reasonably good piezoelectricity at the nanoscale. This study highlights the rich phase evolution of complex ferroelectrics as a novel platform to control the functionality of nanoscale electromechanical devices.

Enhanced strains of Nb-doped BNKT-4ST piezoelectric ceramics via phase boundary and domain design

A strategy that constructs the morphotropic phase boundary and manipulates the domain structure has been used to design the component of 0.96[Bi0.5(Na0.84K0.16)0.5Ti(1-x)NbxO3]-0.04SrTiO3 (BNKT-4ST-100xNb) to enhance the strain properties for actuator application. Non-equivalent Nb5+ donor doping modulates the phase transition from the mixture of rhombohedral and tetragonal phases to the pseudocubic phase and results in the coexistence of multiple phases. Moreover, the high-resolution TEM confirms the existence of polar nano regions that contribute to the macroscopic relaxor behaviour. The size of the domains is reduced with increasing Nb5+, resulting in an enhanced relaxor behaviour. The ferroelectric-relaxor transition temperature decreases from 85 to below 30 °C, implying a non-ergodic to ergodic relaxor transition. An improved strain of 0.56% and a giant normalized strain of 1120 pm/V were achieved for BNKT-4ST-1.5Nb, which were attributed to the unique domain structure in which nanodomains are embedded in an undistorted cubic matrix. Ferroelectric, antiferroelectric, and relaxor phases coexist. As the electric field is large enough, a reversible phase transition occurs. Furthermore, good temperature stability was obtained due to the stability of the nanodomains, and no degradation in strains was observed even after 104 cycles, which may originate from the reversible phase transition and dynamic domain wall. The results show that this design strategy offers a reference way to improve the strain behaviour and that BNKT-4ST-100xNb ceramics could be a potential material for high-displacement actuator applications.

Highly-efficient piezocatalytic performance of nanocrystalline BaTi0.89Sn0.11O3 catalyst with Tc near room temperature

Abstract Inducing changes in polarization of a ferroelectric material by applied stress is recently regarded as a fascinating approach to achieve piezocatalysis in case of both dye degradation and H2 generation. The polarization-driven ferroelectrics are expected to reveal superior performance near Curie temperature (Tc) due to the maximum polarization change, but lack experimental proof. In this work, BaTi0.89Sn0.11O3 (BTS) with high piezoelectric coefficient and low Tc is taken as an example for materials of this kind. BTS nanoparticles with multiple phase coexistence and low Tc ~ 40 °C were prepared and used for dyes degradation and hydrogen generation. In-situ piezoresponse scanning force microscopy revealed a much-enhanced piezoelectric response near Tc, resulting in a highly-active piezocatalyst. The Rhodamine B (RhB) and Methyl orange (MO) could be decomposed within 15 min and 60 min, respectively. Superior H2 generation rates of 141.1 and 360.2 μ mol g−1 h−1 were observed for BTS and BTS@Ag nanoparticles under ultrasonic irradiation at 15 °C. Furthermore, a highly-efficient pyrocatalytic performance with BTS nanoparticles was also found under cold–hot cycle excitation near Tc. This work demonstrates an efficient and low-cost strategy for water remediation via employing low Tc ferroelectrics by harvesting vibration or thermal energy from the surroundings.

MLLPA: A Machine Learning‐assisted Python module to study phase‐specific events in lipid membranes

Machine Learning-assisted Lipid Phase Analysis (MLLPA) is a new Python 3 module developed to analyze phase domains in a lipid membrane based on lipid molecular states. Reading standard simulation coordinate and trajectory files, the software first analyze the phase composition of the lipid membrane by using machine learning tools to label each individual molecules with respect to their state, and then decompose the simulation box using Voronoi tessellations to analyze the local environment of all the molecules of interest. MLLPA is versatile as it can read from multiple format (e.g., GROMACS, LAMMPS) and from either all-atom (e.g., CHARMM36) or coarse-grain models (e.g., Martini). It can also analyze multiple geometries of membranes (e.g., bilayers, vesicles). Finally, the software allows for training with more than two phases, allowing for multiple phase coexistence analysis.

Polymorph co-existence and its implication on transport dynamics in monomer and trimer strontium meta-silicate

Alkali metal doped strontium meta-silicate, a highly conductive system, is being studied as an alternative to solid electrolyte for Solid Oxide Fuel Cells (SOFCs). Its high electrical conductivity is attributed to its structure and dopant strategies. Based on the recent reports, it was observed that it can exist in multiple forms depending upon synthesis route and conditions. The present study deals with the analysis of polymorphism inside strontium meta-silicate (SrSiO3)X using two different configurations viz. monomer (M) corresponding to X = 1 and Trimer (T) corresponding to X = 3, and without any dopant, to ruled out any secondary glassy phase inside the parent compound. The structural analysis showed that for the samples prepared via solid state reaction (SSR) route, the compound contains multiple phases simultaneously irrespective of the temperature and configuration. The present work showed the co-existence and stability of three phases of meta-silicate synthesised via SSR even at high temperatures. The co-existence of multiple phases has led to the enhancement of conductivity by two orders of magnitude in intermediate temperature range of operation for SOFCs.

Ultrahigh piezoelectricity in lead-free piezoceramics by synergistic design

Abstract Following increased environmental concerns on the toxicity of lead, the discovery of ultrahigh piezoelectricity in lead-free piezoelectric materials is critical for the substitution of commercial lead zirconate titanate (PZT) ceramics in numerous electronic devices. In this work, a synergistic design strategy is proposed to enhance the piezoelectricity in lead-free piezoelectric materials by flattening the Gibbs free energy density profile, via the coexistence of multiple phases and local structural heterogeneity. This strategic material design approach is based on first-principles calculations combined with Landau phenomenological theory and phase field simulations. Sustainable Stannum-doped BaTiO3 lead-free ferroelectric ceramics are prepared to validate our proposed mechanism, and a giant piezoelectric coefficient d33 > 1100 pC/N is achieved, being the highest value reported in lead-free piezoceramics. The mechanism and paradigm of the excellent piezoelectricity achieved here provides a feasible solution for replacing lead-based piezoelectrics by lead-free counterparts.

Multiphase coexistence and enhanced piezoelectric properties in (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 lead-free ceramics

A new lead-free piezoelectric solid solution system with the formula of (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 were prepared using a conventional solid-phase sintering method, and we investigated the relationship between the composition, microstructure, phase structure and electrical properties of the ceramics. It was found that adding Bi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 induced the ceramics transition from a single orthorhombic structure to a coexistence of multiple phases, and a three-phase coexistence of rhombohedral, orthorhombic and tetragonal phases was present in the composition range x = 0.03 to 0.035. Enhanced piezoelectric properties were obtained for the ceramics near the three-phase coexistence region, with the largest piezoelectric constant d33 of 253 pC/N and the highest planar electromechanical coupling coefficient of 0.36. Additionally, a rough phase diagram for the solid solution system was established by using the critical temperatures determined by the temperature-dependent dielectric properties. The authors believe that these results can provide a useful reference for the development of (K,Na)NbO3-based lead-free piezoelectric ceramics.