Structural Phase Transformation Research Articles

Size effect on the structural and magnetic phase transformations of iron nanoparticles.

Iron nanoparticles are among the most promising low-dimensional materials in terms of applications. This particularity is attributable to the magnetic properties of these nanoparticles, which exhibit different allotropes as a function of temperature. In this work, we sought to characterise at the atomic scale how their structural and magnetic transformations can be affected by the size. To achieve this objective, we developed a tight-binding model incorporating a magnetic contribution via a Stoner term implemented in a Monte Carlo code to relax the structure and the magnetic state. Using our approach, we show that magnetism is strongly reinforced by the surface, which leads to an increase in the Curie temperature as the size of the particle decreases contrary to the solid-solid transition temperature. Our work thus provides a deep understanding at the atomic scale of the key factors that determine the structural and magnetic properties of Fe nanoparticles, shedding more light on their unique character, which is crucial for further applications.

Features of the Structure Evolution and Phase Transformations During Annealing of the VT22 Titanium Alloy Depending on the Initial State

Features of the Structure Evolution and Phase Transformations During Annealing of the VT22 Titanium Alloy Depending on the Initial State

Nucleation control and separation of ethyl maltol polymorphs under different growth conditions through solution crystallization process in selected solvent environments

Nucleation control, separation and growth of Form-I, II & III polymorphs of ethyl maltol were achieved through solution crystallization processes. Morphology, unit cell structure and polymorphic phase transformations were revealed for the first time.

Strategies to alleviate distortive phase transformations in Li-ion intercalation reactions: an example with vanadium pentoxide.

Chemical and electrochemical Li-ion insertion in transition metal oxides, either via a phase transformation reaction (ions insert into specific crystallographic sites of the host lattice) or a solid solution insertion (ions distribute uniformly throughout the host lattice), enables high energy density electrochemical energy storage. Many phase transformation cathode materials, that undergo two-phase reactions, exhibit high theoretical capacities arising from multi-electron redox reactions. However, challenges in distortive phase transformations and uncontrolled phase nucleation, propagation, segregation, and co-existence continue to limit the energy density, (dis)charging rate performances, and cycling stability of available phase transformation cathode materials. Vanadium pentoxide (V2O5), a classical layered intercalation host material with high theoretical capacity, undergoes irreversible structural changes and capacity fading when intercalating more than one lithium ion per V2O5 unit in its thermodynamically stable phase. Here, we review recent synthetic strategies to alter the V-O connectivity, thereby alleviating distortive phase transformations and promoting solid solution-based Li-ion insertion in V2O5. We also summarize several widely accessible and classical molecular-based analytical tools that can provide local structural dynamics and phase transformation mechanism information on the lithiation of V2O5, including single-crystal X-ray diffraction, infrared and Raman spectroscopy, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopy.

Structural-phase transformations of 12% chromium ferritic-martensitic steel EP-823

The features of phase transformations of 12 % chromium ferritic-martensitic steel EP-823 under heating and cooling conditions in the temperature range from 30 to 1100 ℃ were studied by the methods of high-temperature X-ray diffraction analysis (XRD) in situ and differential scanning calorimetry (DSC). According to XRD in situ data, upon heating, the temperatures of the beginning and end of the (α → γ) transformation of ferrite (martensite – austenite) are Ac1 ≈ 880 °C, Ac3 ≈ 1000 °C, respectively. Upon cooling, a diffusion (γ → α) transformation occurs with critical points – Аr1 ≈ 860°С (beginning temperature) and Аr3 ≈ 840 °С (end temperature). According to DSC data, during heating, the critical points of the (α → γ) transformation are Ac1 ≈ 840 °C and Ac3 ≈ 900 °C. During cooling, a martensitic (γ → α) transformation is realized with critical points of the beginning of Ms = 344 ℃ and the end of Mf = 212 ℃ of this transformation. The XRD in situ analysis revealed no precipitation of carbide phases under heating and cooling conditions of steel EP-823. Position of the critical points of phase transformations depends on the research method (XRD in situ or DSC), which is determined by the difference in effective (taking into account the time for shooting in the XRD method) heating-cooling rate. The effect of elemental composition on the position of critical points of phase transformations and the formation of structural-phase states of ferritic-martensitic steels is discussed. It is shown that the increased content of ferrite-stabilizing elements (Cr, Mo, Nb) in composition of EP-823 steel, compared with other steels of the same class, expands the region of existence of the ferrite phase, which can contribute to an increase in the temperature of Ac1 .

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

AbstractCorundum and transition alumina powders are commonly produced through the Bayer process—that is, by digestion of bauxite in a sodium hydroxide solution, followed by gibbsite precipitation, which contains significant amounts of Na+ ions. During the de‐hydroxylation of gibbsite, Na+ is associated with retardation of the structural phase transformations between transition alumina and corundum (α‐Al2O3) phases, although the exact role of Na is unclear. The influence of Na+ ions on the phase transformation of γ‐Al2O3 to α‐alumina was investigated by varying the concentration of NaOH in aqueous γ‐Al2O3 suspensions. The phase transformation behavior of γ‐Al2O3 was monitored through thermal analysis, X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectrometer (XPS), and transmission electron microscope. As the Na concentration in γ‐alumina suspensions increased, the amount of α‐Al2O3 decreased in samples that were heat treated at 1200°C for 2 h. XPS analysis indicated that washing transition alumina powders with NH4OH solutions had decreased the surface concentration of Na+ and facilitated the phase transformation to α‐Al2O3.

Structure Investigation of Mesogenic Homo- and Copolymers Based on Chiral and Achiral Acrylates

The X-ray diffraction method was used to study the structure of mesogenic homo- and copolymers based on chiral and achiral acrylates (disubstituted biphenyl and phenylbenzoate) under the orienting influence of magnetic and (in some cases) electric fields. The analysis of diffraction patterns was carried out in terms of the Hosemann model of a paracrystal using structural modeling and diffraction calculations on models. It was established that chiral and achiral homopolymers form smectic bilayer polar structures, but the structure of the achiral homopolymer possesses weak polarization due to small value of total dipole moment of C=O groups in the side chains. The copolymers (as the chiral homopolymer) form smectic bilayer polar helicoidal structures. The distribution of chiral and achiral components in the layers of the common bilayer depends on their ratios in the copolymer. In turn, this distribution affects both the step of helicoidal structure and the nature of structural-phase transformations in the copolymers. A comparative evaluation of the orientational effects of magnetic and electric fields on the structure of the chiral homopolymer and the copolymers has been carried out. The analysis of the temperature dependences of diffraction and structural parameters of the investigated polymers allowed us to explain some features of their behaviour within seemingly similar (by the type of X-ray patterns) smectic phases.

Synthesis of novel nanocomposite of g-C3N4 coated ZnO–MoS2 for energy storage and photocatalytic applications

Fabrication of heterostructures for energy storage and environmental remedial applications is an interesting subject of research that has been undertaken in this present investigation. The incorporation of g-C3N4 into ZnO:MoS2 heterojunction nanocomposite was accomplished by wet-chemical route and characterized by various techniques to ascertain its structure, morphology, and study its potential electro-optical characteristics. The g-C3N4@ZnO:MoS2 sample was investigated by x-ray diffraction (XRD) which reveals the co-existence of the ZnO, MoS2 and C3N4 phases linked to characteristic crystallographic planes in the spectrum, validating the formation of ternary nanocomposite. The XRD patterns of the pristine samples were also considered as reference to understand the structural evolution and phase transformations. Field emission scanning electron microscopy (FESEM) study states the formation of heterogeneous nanostructures having nanoparticles embedded on 2-D nanosheets like structures. Studies using energy dispersive spectroscopy (EDS) and elemental mapping show that all the elements that are linked to the above hybrid nanocomposite are present. Transmission electron microscopy (TEM) provided clear insights on the microstructure as we can identify the distribution of ZnO and MoS2 nanostructures on layered g-C3N4 nanosheets. The chemical composition and oxidation states of elements were elucidated by X-ray photoelectron spectroscopy (XPS) study, which added another layer of confirmation on the structural evolution of the ternary nanocomposite. Fourier transformed infrared (FTIR) study revealed the layered structure of sp2 hybridized bonding features of C and N in g-C3N4, besides Zn–O and Mo–S stretching vibrations. The nanocomposite demonstrated improved photodegradation efficacy and decomposed alizarin red and methylene blue dyes significantly with better stability and reusability. MoS2 as a co-catalyst acts as an electron acceptor/accelerator in the Z-scheme composite photocatalysis leading to improved photocatalytic efficiency. The resulting heterostructured material delivered a higher specific capacitance of 10.85 F/g with good capacitance retention. Electrochemical study revealed the energy storage capability of the hybrid system.

Stabilizing Cobalt-Free Li-Rich Layered Oxide Cathodes By Site-Specific Doping

The limited theoretical capacity of traditional cathode materials solely based on transition metal (TM) redox has been a primary factor for the ceiling placed on the energy density of LIBs. In this regard, Li-rich layered oxides (LLOs) have received a great deal of attention, due to their high reversible capacity (> 250 mAh g-1) and high energy density (900 Wh kg-1), courtesy of the TM redox and the additional high-voltage O2- redox.1, 2 Although the electrochemical performance of Co-free LLOs is significantly less satisfactory, developing Co-free cathodes is inevitably a holy grail owing to cobalt’s economic, ethical, and political issues caused by high-cost toxicity. Therefore, studies on Co-free LLOs are necessary for creating long-term benefits for the cathode industry.Unfortunately, Co-free LLOs suffer from capacity and voltage decay on cycling, which for now obviously limits the materials use outside the academics laboratory. It is well accepted that that performance decay is primarily attributed to the irreversible anionic redox and structural degradation in LLOs. The doping strategy has been widely used to address the voltage decay of LLOs.3 While the dopant is typically introduced to the layered R m component, the lithium-rich component (C2/c) in the LLOs, which is the source of anionic redox, has always been ignored.Our team comprehensively investigates the structural involution of LLOs based on a Co-free Li-rich Mn-based Li1.2Ni0.2Mn0.6O2 (LNMO) cathode using in-operando and ex-situ synchrotron-based characterizations. We learned through mechanistic characterization that the transition from the monoclinic (C2/c) to the hexagonal (R-3m) behaviour is an intrinsic behaviour of LLOs for the first time. According to this structure-function relationship, we introduced a small quantity of one electrochemically active metal, ruthenium, into both R-3m and C2/c components in LNMO and found that the oxygen lattice and structural stability can be significantly improved by the site-specific doping against lithiation and delithiation processes.4 Additionally, reducing the irreversible TM migration is key to advancing the performance of layered oxide cathode materials. Contrary to many previous studies that emphasize suppressing cation migration, our team proposed that reversible tetrahedral-octahedral TM migration helps inhibit the formation of undesirable structural changes and phase transformation. The oxidation state of TM, such as Ni, Mn, and Co, are easily trapped into the octahedral sites in the Li layer due to their high octahedral-site splitting energy when a large amount of Li has extracted from the structure. By introducing Cr into LNMO, we found that Cr can migrate reversibly between the tetrahedral and octahedral sites, which makes Cr-doped LNMO possess significantly enhanced structural stability and thus achieve higher electrochemical performance than LNMO.In all, our research focuses on the site-specific doping of the Co-free LLOs and understanding the structure- and chemistry-function relationship of the LLOs. The findings in our work might provide possible pathways for the future design of high-performance cathode materials for lithium-ion batteries and may also apply to developing cathode materials for other energy storage systems.Reference S. Hu, A. S. Pillai, G. Liang, W. K. Pang, H. Wang, Q. Li and Z. Guo, Electrochem. Energy Rev., 2019, 2, 277-311.M. Han, J. Jiao, Z. Liu, X. Shen, Q. Zhang, H.-J. Lin, C.-T. Chen, Q. Kong, W. K. Pang, Z. Guo, R. Yu, L. Gu, Z. Hu, Z. Wang and L. Chen, Adv. Energy Mater., 2020, 10, 1903634.Y. Fan, W. Zhang, Y. Zhao, Z. Guo and Q. Cai, Energy Stor. Mater., 2021, 40, 51-71.Y. Fan, E. Olsson, G. Liang, Z. Wang, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, J. Li, F. Zhang, Y. Zhao, W. K. Pang, Q. Cai and Z. Guo, Angew. Chem. Int. Ed., 2022, DOI: 10.1002/anie.202213806.

Raman spectroscopy study and dielectric anomalies in Bi1-xEux AFM FeO3 thin films.

BiFeO3 is a multiferroic material, so its ferroelectric and ferromagnetic properties are coupled. Due to the presence of magneto-electric coupling in the system, magnetic changes are obvious in the dielectric spectra. As a thin film of BFO exhibits a weak magnetic moment, dielectric analysis can be utilized to observe different magnetic transitions. In the present work, thin films of Eu3+ substituted BiFeO3 are prepared to stabilize the Perovskite phase. The role of Eu3+ substitution in triggering the structural phase transformation is analyzed using Raman analysis. Capacitance and dissipation spectrum as a function of temperature for various Eu3+ concentrations are studied in detail. The presence of various transitions is observed in the dielectric permittivity. The possible origin of the transitions in permittivity spectra is discussed in terms of spin-lattice and charge interactions and their degrees of freedom. Substitution with rare-earth ions significantly affects the system's magnetic characteristic, including contribution from magnetization from sub-lattice and magnetic anisotropy. Eu3+ substitution led to the change in the spin reorientation axis, which has been explained in terms of phenomenological and microscopic variation in magnetization due to the contribution from the rare earth ion.

Вплив аргонвмісного середовища відпалу на перебіг структурно-фазових перетворень в тонкоплівкових композиціях Ni/Ti

This study is focused on the effect of isothermal annealing in an argon atmosphere (200 Pa) in the temperature range of 200–600 °C on the evolution of diffusion-induced structural phase transformations in Ni/Ti layered thin films with different modulation period but similar total thickness of 60 nm. Changes in the structure and phase composition of nanoscale films have been examined using X-ray diffraction technique, and the chemical composition has been analyzed using secondary ion mass spectrometry. Annealing at 300 °C induces the development of diffusion interaction between the Ni and Ti layers, leading to the formation of intermetallic NixTiy phases of various stoichiometry at higher annealing temperatures. It is shown that an increased number of layers promotes a significant activation of diffusion processes between the components of the system, resulting in a change in its phase composition at lower annealing temperatures. Meanwhile, for all investigated samples, annealing at elevated temperatures (>500 °C) causes the agglomeration of Ti on the free surface with the probable formation of a protective oxide layer. It was established that the decisive influence on thermally induced phase formation is exerted by two competing factors: the use of an argon-containing annealing atmosphere contributes to the intensification of mass transfer processes between the materials of metal nanolayers compared to similar heat treatment in a vacuum, while the decrease of the modulation period of the thin-film system promotes the amorphization processes at the interface between metal layers with a corresponding inhibition of structural ordering processes. Keywords: nanoscale films, NiTi, diffusion, argon, isothermal annealing.

Study of Structure-Phase Transformations during Hydrogen Desorption by a VT1-0 Titanium Alloy and an E110 Zirconium Alloy

Study of Structure-Phase Transformations during Hydrogen Desorption by a VT1-0 Titanium Alloy and an E110 Zirconium Alloy

Experimental investigations on the microstructural evolution and their influence on mechanical, tribological and corrosion performance of wire-arc additive manufactured SS316L structure

The study investigates the feasibility of emerging wire arc additive manufacturing technology to fabricate steel structures. The grain morphology and phase transformation of the WAAM-printed structure have been thoroughly examined and investigated their influence on the mechanical, tribological, and corrosion performance. The structure is characterized by fine equiaxed grains nearer to the cold substrate and coarse columnar grains along the upper regions. The average grain size in the top, middle, and bottom regions of the printed wall is 12.34 ± 5.81 µm, 10.27 ± 2.84 µm, and 4.33 ± 0.89 µm respectively. The higher temperature gradient in the bottom regions led to the ferrite-austenite solidification mode that switched toward the primary austenite solidification mode in the upper layers. The printed parts witness superior mechanical properties with an improved micro-hardness and tensile strength however reduced ductility compared to the conventionally produced steel. The longitudinal direction of the printed parts experienced slightly higher hardness than the transverse. The tribological performance in different regions is investigated under different loading conditions and discovered an improvement in the wear-resistant properties of the fabricated part to its wrought counterpart even at high load conditions. Moreover, comparative corrosion resistance properties of the WAAM and wrought steel were detected with a slightly higher corrosion rate along the upper region in a moderately saline environment with flowing and stagnant conditions. The study detects the dependence of the characteristics properties on the grain morphology and existing phases in different regions of the arc additive-manufactured steel wall.

Effect of silver doping on electrical characteristics of aluminum/HfO2/p-silicon metal-oxide-semiconductor devices

In this study, undoped and silver (Ag) doped hafnium oxide (HfO2) thin films were prepared by sol-gel dipping method and their effect as an interface material in a p-Si-based metal-oxide-semiconductor device was investigated for the first time. The structural effects of Ag doping were investigated using x-ray diffraction patterns. Al/HfO2:Ag/p-Si devices were fabricated using these films, and their electrical properties were characterized by measuring current-voltage (I–V) curves at room temperature. The ideality factor values of the devices decreased from 4.09 to 2.20 as the Ag doping ratio increased. Simultaneously, the barrier height values increased from 0.60 eV to 0.81 eV. The calculated series resistance values, determined by two different methods, demonstrated that the lowest resistance values were obtained at a 1% Ag doping ratio. Furthermore, the interface state densities were found to vary with the doping ratio. The improvement in electrical parameters resulting from Ag doping can be attributed to the reduction in molar volume due to structural phase transformation. The decrease in the ideality factor suggests enhanced carrier transport efficiency, while the increase in barrier height indicates improved energy band alignment at the metal/semiconductor interface.

Correlating Phonons and Deformations: A Method for Structural Phase Transformation Analysis in Metal–Organic Frameworks

Correlating Phonons and Deformations: A Method for Structural Phase Transformation Analysis in Metal–Organic Frameworks

Enhanced thermoelectric and mechanical properties of polycrystalline cubic SnSe by AgBiTe2 alloying

Recently, the cubic SnSe with multiple valleys and low thermal conductivity has become the focus of current research and receives extensive attention worldwide. However, the cubic SnSe is difficult to exist stably at normal temperature and pressure. In this work, the cubic rock-salt SnSe samples were successfully stabilized at room temperature by AgBiTe2 alloying. Microstructure and thermoelectric properties of the Sn1–2x(AgBi)xSe1–2xTe2x (x = 0, 0.10, 0.15, 0.20, 0.25, 0.30) were studied systematically. With the increase of AgBiTe2 addition, the crystal structure of SnSe gradually transformed from orthorhombic to cubic phase. Due to the doping of heterogeneous atoms and the phase structural transformation, the carrier concentration and carrier mobility of Sn1–2x(AgBi)xSe1–2xTe2x were optimized, thus the electrical properties were significantly enhanced. An obviously enhanced zTmax of 0.70 at 750 K and a zTave of 0.29 (300–750 K) were achieved in Sn0.50(AgBi)0.25Se0.50Te0.50. In addition, the mechanical properties of Sn1–2x(AgBi)xSe1–2xTe2x were also strengthened. A higher Vickers hardness of ∼1.8 GPa was obtained in Sn0.40(AgBi)0.30Se0.40Te0.60.

Study of the Effect of Adding Nb2O5 on Calcium Titanate-Based Ferroelectric Ceramics

This paper considers the effect of adding niobium oxide (Nb2O5) to ferroelectric ceramics based on calcium titanate (CaTiO3), and establishes a connection between the observed alterations in strength and dielectric properties and the variation in the Nb2O5 dopant concentration in the ceramics’ composition. The method of mechanochemical solid-phase synthesis was used as the main method for obtaining the ceramics, followed by thermal sintering under specified conditions in order to form a stable phase composition of the ceramics, and to initialize phase transformations in the composition. Based on the assessment of the phase composition of the resulting ceramics, it was determined that a growth in the Nb2O5 dopant concentration beyond 0.10 mol results in the formation of an orthorhombic-phase CaNb2O4 of the Pbcm(57) spatial system, the weight contribution of which grows. A growth in the Nb2O5 additive concentration results in the formation of two-phase ceramics, the formation of which allows for an enhancement in the mechanical strength of ceramics and resistance to external influences. During the study of the dependence of the strength properties on the dopant concentration alteration, a three-stage change in hardness and crack resistance was established, regarding both structural ordering and phase transformations. The measurement of dielectric characteristics showed the direct dependence of dielectric losses and the dielectric constant on the phase composition of ceramics.

A Review of Electric Potential-Controlled Boundary Lubrication

Tribotronics represents the modulation of friction via an external electric potential, a field with promising ramifications for intelligent devices, precision manufacturing, and biomedical applications. A profound elucidation of mechanisms that allow for potential-controlled friction is foundational to further research in this tribotronic domain. This article provides a comprehensive review of the research progress in electro-controlled friction over the past few decades, approached from the perspective of the boundary lubrication film at the friction interface, a direct influencer of electro-controlled friction performance. The mechanisms of potential-controlled friction are categorized into three distinct classifications, contingent on the formation mode of the boundary lubrication film: potential-induced interfacial redox reactions, interfacial physical adsorption, and interfacial phase structure transformations. Furthermore, an outlook on the application prospects of electro-controlled friction is provided. Finally, several research directions worth exploring in the field of electro-controlled friction are proposed. The authors hope that this article will further promote the application of electro-controlled friction technology in engineering and provide intellectual inspiration for related researchers.

High-entropy (YErYbLu)2SiO5 ceramic aerogel: A potential ceramic insulator with low thermal conductivity

Conventional oxide aerogels have limitations in terms of structural damage and phase transformation at high temperatures. A novel high-entropy (YErYbLu)2SiO5 ceramic aerogel was synthesized by a combination of the sol-gel process, supercritical drying, and high-temperature calcination. The successful synthesis of a high-entropy (YErYbLu)2SiO5 ceramic aerogel in a single phase after calcination at 1250 °C was confirmed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The high-entropy ceramic aerogel (YErYbLu)2SiO5 still shows excellent structural and phase stability after annealing at 1400 °C. The structurally reconstructed samples (RSO) exhibit low densities ranging from 1.79 to 3.28 g/cm3, room-temperature thermal conductivities between 0.109 and 0.253 W·m-1 K-1, and fracture toughness values ranging from 0.61 to 9.70 MPa. Notably, the lowest thermal conductivity is less than 1/10 of that of the corresponding dense crystalline ceramics. Furthermore, the RSO has a low coefficient of thermal expansion within the temperature range of 360–1200 °C (ranging from 5.84 × 10−6 °C−1 to 7.36 × 10−6 °C−1). The RSO exhibits high residual strength retention after thermal shock testing. These properties position the high-entropy (YErYbLu)2SiO5 ceramic aerogel as a promising candidate for nano-thermal insulation as a porous ceramic material that undergoes structural reconstruction.