Structural Phase Transformation Research Articles

First‐principles calculations on LaX3 (X: Sb, Sn) as electrode material for lithium‐ion batteries

AbstractUsing first‐principle calculations, we investigate the rare‐earth intermetallic compound LaX3 (X = Sb and Sn) as a cathode material for rechargeable lithium‐ion batteries (LIBs). The calculations have been performed to look into the stability of the structure and the electronic properties of host LaX3 as well as its lithiated phases, LixLa1−xX3 (0 < x ≤ 1). In this study, we have observed a structural phase transformation of these intermetallic compounds from a cubic to a tetragonal structure upon lithiation to host structure. The ground state energy is calculated using the WIEN2k package to determine the structure stability and volume change due to lithium addition, which is further used to calculate the formation energy, open circuit voltage (OCV), and lithium‐ion storage capacity. The equilibrium structural parameters for all the phases are determined by achieving a total energy convergence of 10−4 Ry. The estimated band structure along high‐symmetry lines in the first Brillouin zone and the total as well as partial density of states demonstrate unequivocally that the addition of lithium does not change the metallic nature of these electrode materials. We have also calculated the theoretical lithium‐ion storage capacity and OCV for all the compounds. Despite a higher value for OCV larger than 5 V, many of the investigated materials could not be found suitable from a synthesis point of view due to positive formation energies. The formation energy calculation shows that LaSb3, with a 50% concentration of Li, is the most stable compound out of those investigated here. The calculated OCV for Li0.5La0.5Sb3 is 4.27 V. This is substantially higher than the value obtained up to this point for LIBs, which ranges from 3.20 to 3.65 V/cell. These improved results related to the most stable alloy (Li0.5La0.5Sb3) investigated in this work indicate that it is necessary to check the experimental feasibility of its synthesis and actual device performance.

Molecular design of highly Li-ion conductive cathode-electrolyte interface enabling excellent rate performance for lithium-ion batteries

The structural stability and ionic conductivity of the cathode electrolyte interface (CEI) film at high voltages are crucial to the nickel-rich layered cathode in Li-ion batteries (LIBs). These characteristics are largely determined by electrolyte components. Herein, an air-stable organic cyclophosphate salt named lithium 1, 3, 2-dioxaphosphinan-2-olate-2-oxide (LiDOP) is designed and synthesized as a CEI forming additive. It preferentially oxidizes and undergoes opening-ring polymerization under charging to form an organic–inorganic hybrid polymers with –LiPO4 segments and –(CH2)3– alternately connected on the cathode surface. Such a structure endows CEI film with high ionic conductivity, flexibility and mechanical strength, which can ameliorate the structure phase transformation, suppress the transition metal ion dissolution and enhance the interfacial stability at high cut-off voltage. The electrolyte with 0.2 wt% LiDOP endows 4.3 V-charged Li||LiNi0.8Co0.1Mn0.1O2 battery with 83.2 % capacity retention after 200 cycles at 5C rate. The graphite||NCM811 pouch cell shows a capacity retention of 85.6 % after 150 cycles under a 4.5 V voltage, while the cell without LiDOP shows only 23.5 %. Our work demonstrates the effectiveness of covalently coupled P-O-Li compounds as CEI film in stabilizing the interface, which provides a guidance for the electrolyte design in high-voltage LIBs.

Solvent-Responsive Nonporous Adaptive Crystals Derived from Pyridinium Hydrochloride and the Application in Iodine Adsorption.

Nonporous adaptive crystals (NACs) are crystalline nonporous materials that can undergo a structural adaptive phase transformation to accommodate specific guest via porous cavity or lattice voids. Most of the NACs are based on pillararenes because of their flexible backbone and intrinsic porous structure. Here a readily prepared organic hydrochloride of 4-(4-(diphenylamino)phenyl)pyridin-1-ium chloride (TPAPyH), exhibiting the solvent dimension-dependent adaptive crystallinity is reported. Wherein it forms a nonporous α crystal in a solvent with larger dimensions, while forming two porous β and γ crystals capable of accommodating solvent molecules in solvent with small size. Furthermore, the thermal-induced single-crystal-to-single-crystal (SCSC) transition from the β to α phase can be initiated. Upon exposure to iodine vapor or immersion in aqueous solution, the nonporous α phase transforms to porous β phase by adsorbing iodine molecules. Owing to the formation of trihalide anion I2Cl- within the crystal cavity, TPAPyH exhibits remarkable performance in iodine storage, with a high uptaking capacity of 1.27 g g-1 and elevated iodine desorption temperature of up to 110 and 82°C following the first and second adsorption stage. The unexpected adaptivity of TPAPyH inspires the design of NACs for selective adsorption and separation of volatile compound from organic small molecules.

Local electronic structures of annealing induced phases in cobalt doped TiO2 nanoparticles: a combined study of transmission electron microscopy and x-ray absorption fine structure spectroscopy

The evolution of the nanostructures and electronic properties of 5% cobalt-doped TiO2 nanoparticles (NPs) annealed at 400 °C, 600 °C, and 800 °C have been investigated to understand the structural phase transformations through chemical co-precipitation synthesis. A detailed analysis of the X-ray Diffractogram confirms that the sample annealed at 400 °C is anatase, at 600 °C, the mixed phase of anatase and rutile evolves, and at 800 °C, the sample is of rutile structure. A detailed morphological study by scanning transmission electron microscope provides the particle size, lattice spacing, and variation in polycrystalline grain growth at different phases. Electron Energy Loss Spectroscopy analysis indicates from the O K, Co, and Ti L 2,3-edges that Ti4+ ions are primarily in an octahedral symmetry with the oxygen ligands changing their structural phases from anatase to mixed phase and then stable rutile phase with increasing temperature of annealing. X-ray Absorption Near Edge Spectroscopy (XANES) extracts information about the varying oxidation states and 3-dimensional geometry of Ti-ions. The unresolved issues of the structural details at the atomic-scale picture with the local environment of the cation with a few nearest neighbour shells are derived from Extended X-ray Absorption Fine Structure (EXAFS) and pre-edge parts of the absorption spectra. The limits of EXAFS in this situation of asymmetric bond length disorder, which is typical for mixed-valence oxides, are generated to reconcile the two data and highlight the value of pre-edge XANES analysis for identifying local heterogeneities in structural and compositional motifs. TiO2 possesses unique properties depending upon its structural phase. The Ti L 2,3-edge spectrum indicates that there is an octahedron connectivity of the Oxygen atoms at the anatase state which transforms to a higher energetic tetrahedral correspondence as it proceeds towards the rutile phase. The driving force behind such interest is to modulate the properties of TiO2 NPs to better photocatalytic material and to integrate its application as a versatile energy storage device.

Structural Order-Disorder Analysis of Thermally-Activated Water-Washed Kaolin Particles Using Fourier Transform Infrared Spectroscopy

During the calcination of kaolin particles, kaolinite is thermally activated at high temperatures, causing the crystal structure to collapse and yielding amorphous metakaolinite through dehydroxylation. This metakaolinite is used as a supplementary cementitious material, and one of the most important factors influencing the pozzolanic properties is calcination conditions. Fourier transform infrared spectroscopy (FTIR) has become useful in distinguishing and obtaining information about structural order-disorder and phase transformation following the calcination process. In this study, water-washed kaolin particles were thermally activated at elevated temperatures ranging from 600 to 800 °C for 3–4 h at a rate of 10 °C/min before being analyzed with FTIR to determine the optimum conditions for calcining kaolin particles by examining functional groups, and also to study structural order-disorder or crystallinity of calcined kaolin particles. The most reactive metakaolinite state of water-washed kaolin particles was achieved after 3 h of calcination at 800 °C. Using both empirical and numerical approaches, variations in the position and relative intensity of O-H stretching and deformation of hydroxyl groups in the infrared spectrum can be used to classify the degree of structural order of water-washed kaolin particles. By increasing the calcination temperatures and period, the well-ordered and partially-ordered structures of kaolin particles were transformed into well-ordered, partially-ordered, and poorly-ordered structures. These structural disorder and crystallinity have a significant impact on pozzolanic activity because well-ordered kaolinite can be transformed into less reactive metakaolinite, whereas poorly-ordered kaolinite with high defects can be transformed into more reactive metakaolinite. However, in this study, the structure of water-washed kaolin particles that achieved complete dehydroxylation was discovered to be partially-ordered to poorly-ordered and can be transformed into highly reactive pozzolans.

Study of Structural-Phase Transformations and Kinetics of Decomposition of Supersaturated Solid Solution of Fire-Resistant Magnesium Alloy VML26

Study of Structural-Phase Transformations and Kinetics of Decomposition of Supersaturated Solid Solution of Fire-Resistant Magnesium Alloy VML26

СТРУКТУРА И СВОЙСТВА ПОРОШКОВЫХ МАТЕРИАЛОВ НА ОСНОВЕ МЕХАНОСИНТЕЗИРОВАННЫХ МЕТАЛЛОМАТРИЧНЫХ КОМПОЗИТОВ Ni-TiC

The article considers the mechanochemical preparation of TiC-Ni composites in reaction mixtures of Ti-C-Ni powders and the formation of the structure of materials during their sintering under pressure. The synthesis was carried out in an AGO-2 planetary ball mill with a mixture processing time of 12 and 20 min; their subsequent sintering was performed at a temperature of 950 °C and a pressure of 130 MPa. The results of diffraction studies are presented for structural-phase transformations in mixtures of equimolar composition of titanium and carbon depending on the nickel content in the range of 50–70 wt.%. It is established that an increase in the Ni concentration leads to a decrease in the size of the formed TiCx crystallites from 29 ± 1 to 16 ± 1 nm. A high carbon content TiC0.88–0.98 carbide is formed in Ti-C-(50 and 60 %)Ni compositions and non-stoichiometric TiC0.62–0.78 at 70 % Ni. The microstructure of dispersion-strengthened grains of the nickel solid solution is formed during sintering of TiC/(50–60 %)Ni mechanocomposites. Titanium carbide inclusions have a spherical shape and a diameter of 60–100 nm. When sintering TiC/70%Ni, depleted titanium carbide has a grain boundary distribution with the formation of large (~400 nm) agglomerates. The microhardness of sintered materials is in the range of 850–900 HV.

Development of Promising Steels for Railway Rails of a New Generation Using Modeling of Phase-Structural Transformations

Development of Promising Steels for Railway Rails of a New Generation Using Modeling of Phase-Structural Transformations

Low-temperature diffusion in thin-film Pt-(Au-)-Co heterostructures: a structural and magnetic characterization

Formation of functional thin films for nanoelectronics and magnetic data storage via thermally induced diffusion-driven structural phase transformations in multilayer stacks is a promising technology-relevant approach. Ferromagnetic thin films based on Co Pt alloys are considered as a material science platform for the development of various applications such as spin valves, spin orbit torque devices, and high-density data storage media. Here, we study diffusion processes in Pt–Co-based stacks with the focus on the effect of layers inversion (Pt/Co/substrate versus Co/Pt/substrate) and insertion of an intermediate Au layer on the structural transitions and magnetic properties. We demonstrate that the layer stacking has a pronounced effect on the diffusion rate at temperatures, where the diffusion is dominated by grain boundaries. We quantify effective diffusion coefficients, which characterize the diffusion rate of Co and Pt through the interface and grain boundaries, providing the possibility to control the homogenization rate of the Pt–Co-based heterostructures. The obtained values are in the range of 10−16–10−13 cm2 s−1 for temperatures of 150 °C–350 °C. Heat treatment of the thin-film samples results in the coercivity enhancement, which is attributed to short-range chemical ordering effects. We show that introducing an additional Au intermediate layer leads to an increase of the coercive field of the annealed samples due to a modification of exchange coupling between the magnetic grains at the grain boundaries.

Effects of structural strain and phase transformations on the mechanical properties of alumina-zirconia-graphene composites

Yttria-stabilized-zirconia (YSZ) plus graphene-based-materials composites may present phase transitions. Consequently, it may affect the composite properties. Thus, this work discusses the causality between lattice strain, phase transition, fracture toughness (Kc) and hardness (H) values in alumina+YSZ matrix reinforced with 0 wt.% up to 1.25 wt.% multilayered-graphene (MLG). The conventional sintering was made in a reducing atmosphere. H and Kc were obtained by Vickers indentation. The structural characterization shows that the MLG addition promoted an increase in YSZ lattice parameters and a phase transition, from tetragonal to cubic. As a result, the optimum reinforcement peak in the H and in the Kc happens in different MLG concentrations. The Kc optimum is in lower MLG amount, explained by microstructural features. On the other hand, the optimum H displaced to higher MLG concentration may be effect of increasing lattice parameters and the cubic-YSZ phase proportion.

Alkaline Water Electrolysis for Green Hydrogen Production.

ConspectusThe global energy landscape is undergoing significant change. Hydrogen is seen as the energy carrier of the future and will be a key element in the development of more sustainable industry and society. However, hydrogen is currently produced mainly from fossil fuels, and this needs to change. Alkaline water electrolysis with advanced technology has the most significant potential for this transition to produce large-scale green hydrogen by utilizing renewable energy. The assembly of industrial electrolyzer plants is more complex on a larger scale, but it follows a basic working principle, which involves two half-cells of anode and cathode sites where the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) occur. Out of the two reactions, the OER is more challenging both thermodynamically and kinetically. Besides having access to renewable electricity, developing durable and abundant electrocatalysts for the OER remains a challenge in large-scale alkaline water electrolysis. Among different physicochemical properties, the electrocatalyst surface and its interaction with water and reaction intermediates, as well as formed molecular hydrogen and oxygen, play an essential role in the catalytic performance and the reaction mechanism. In particular, the binding strengths between the catalyst surface and intermediates determine the rate-limiting step and electrocatalytic performance.This Account gives some insights into the status of the hydrogen economy and basic principles of alkaline water electrolysis by covering its fundamentals as well as industrial developments. Further, the HER and OER reaction mechanisms of alkaline water electrolysis and selected electrocatalyst progress for both half-reactions are briefly discussed. The Adsorbate Evolution Mechanism and the Lattice Oxygen Mechanism for the OER are explained with specific references. This Account also deliberates on the author's selected contributions to the development of transition metal-based electrocatalysts for alkaline water electrolysis with an emphasis on OER. The focus is particularly given to the enhancement of intrinsic activity, the role of eg-filling, phase segregation, and defect structure of cobalt-based electrocatalysts for OER. Structural modification and phase transformation of the cobalt oxide electrocatalyst under working conditions are further deliberated. In addition, the creation of new active surface species and the activation of cobalt- and nickel-based electrocatalysts through iron uptake from the alkaline electrolyte are discussed. In the end, this Account provides a brief overview of challenges related to large-scale production and utilization of green hydrogen.

Femtosecond Laser-Induced Phase Transformation on Single-Crystal 6H-SiC.

Silicon carbide (SiC) is widely used in many research fields because of its excellent properties. The femtosecond laser has been proven to be an effective method for achieving high-quality and high-efficiency SiC micromachining. In this article, the ablation mechanism irradiated on different surfaces of 6H-SiC by a single pulse under different energies was investigated. The changes in material elements and the geometric spatial distribution of the ablation pit were analyzed using micro-Raman spectroscopy, Energy Dispersive Spectrum (EDS), and an optical microscope, respectively. Moreover, the thresholds for structural transformation and modification zones of 6H-SiC on different surfaces were calculated based on the diameter of the ablation pits created by a femtosecond laser at different single-pulse energies. Experimental results show that the transformation thresholds of the Si surface and the C surface are 5.60 J/cm2 and 6.40 J/cm2, corresponding to the modification thresholds of 2.26 J/cm2 and 2.42 J/cm2, respectively. The Raman and EDS results reveal that there are no phase transformations or material changes on different surfaces of 6H-SiC at low energy, however, decomposition and oxidation occur and then accumulate into dense new phase material under high-energy laser irradiation. We found that the distribution of structural phase transformation is uneven from the center of the spot to the edge. The content of this research reveals the internal evolution mechanism of high-quality laser processing of hard material 6H-SiC. We expect that this research will contribute to the further development of SiC-based MEMS devices.

Strain-tuned optical properties of bilayer silicon at midinfrared wavelengths

Optical properties of two-dimensional bilayer silicon have been explored at midinfrared wavelengths using density functional theory. In this work, progressive atomic structural deformation and the resultant variations in the optical properties of the bilayer silicon films were investigated under external in-plane strain. A phase transformation of the atomic structure has been observed at an applied in-plane tensile strain of 5.17%, at which the atomic lattice is changed from a low buckled to a buckle-free honeycomb structure. Evaluations of the optical properties were carried out by taking into account the inter- and intraband transitions. An abrupt change in the optical refraction index was observed at the phase transition. In addition, the buckle-free honeycomb structure presents a strain-resistive absorption edge pinned at 1.14 μm wavelength. Exceeding a strain threshold of 12.26% results in the development of both direct- and indirect-energy bandgap openings. The direct bandgap induced interband optical transitions, resulting in absorption peaks at midinfrared wavelengths and a drastic increase in the refraction index. Moreover, by adjusting the strain, the optical absorptions can be tuned in a wide range of wavelength at midinfrared from 1.5 to 11.5 μm.

Impact of palladium/palladium hydride conversion on electrochemical CO2 reduction via in-situ transmission electron microscopy and diffraction

Electrochemical conversion of CO2 offers a sustainable route for producing fuels and chemicals. Pd-based catalysts are effective for converting CO2 into formate at low overpotentials and CO/H2 at high overpotentials, while undergoing poorly understood morphology and phase structure transformations under reaction conditions that impact performance. Herein, in-situ liquid-phase transmission electron microscopy and select area diffraction measurements are applied to track the morphology and Pd/PdHx phase interconversion under reaction conditions as a function of electrode potential. These studies identify the degradation mechanisms, including poisoning and physical structure changes, occurring in PdHx/Pd electrodes. Constant potential density functional theory calculations are used to probe the reaction mechanisms occurring on the PdHx structures observed under reaction conditions. Microkinetic modeling reveals that the intercalation of *H into Pd is essential for formate production. However, the change in electrochemical CO2 conversion selectivity away from formate and towards CO/H2 at increasing overpotentials is due to electrode potential dependent changes in the reaction energetics and not a consequence of morphology or phase structure changes.

The use of diffraction techniques for understanding structure–property relationships in Heusler alloys

Heusler compounds are intermetallic alloys that are capable of a wide range of unique properties such as magnetocaloric, thermoelectric, and magnetic-shape-memory effects, antiferromagnetism, superconductivity, and they can even act as topological insulators. These multifunctional behaviors make Heusler alloys prime candidates for numerous smart device applications. However, their specific properties critically depend on their crystalline structures, chemical order, structural phase transformations, and crystallographic texture. Thus, as compositions and processing parameters are varied it becomes essential to be able to accurately characterize the structure of these materials at various scales. This paper provides a brief review of diffraction-based characterization techniques ideally suited for the characterization of Heusler alloys with examples from our previous works including use of synchrotron, neutron, and electron diffraction, especially as a function of temperature and/or magnetic field to explain important phenomena demonstrated by Heusler alloys.

A comparative investigation of structural, magnetic and photocatalytic properties of pure, Ce-Ni and Cd-Ni co-doped BiFeO3 nanoparticles

Bismuth ferrite, BiFeO3 (BFO) as well as Ce-Ni, Cd-Ni co-substituted BiFeO3 nanoparticles were prepared using the sol–gel route. XRD and Raman results show a structural phase transformation from rhombohedral (pristine BFO) to orthorhombic in the case of Bi0.94Cd0.06Fe0.94Ni0.06O3 (BCdFNO6), which implies that Cd substitution can induce the obvious transition of crystal structure while Ce substitution Bi0.94Ce0.06Fe0.94Ni0.06O3 (BCeFNO6) cannot. An apparent blue shift can be noted in all the substituted samples and with a reduction of the direct optical bandgap compared with the pristine BFO. The XPS findings show that Ce-Ni and Cd-Ni substitution increases the Fe3+ ions (Cd-Ni co-doped samples reveal the best outcomes), which would be evidence for reducing oxygen vacancies and improving magnetism. Cd-Ni co-substituted into BFO can improve magnetic properties because the ionic radii of Cd2+ ion are smaller than that of Bi3+ ion; moreover, intriguingly, the room temperature magnetic (M−H) hysteresis loops reveal the greatest saturation magnetization value in Cd-Ni co-substituted samples. The co-doped of Cd-Ni, has the greatest degradation activity 99.48 % of MB and 98.76 % of RhB would be successes after 90 min irradiation, which was raised by 9.49 %, 25 % of MB and 9.52 %, 26.92 % of RhB from that of the Ce-Ni co-doped and pristine BFO.

X‐ray imaging for structural evolution and phase transformation dynamics of battery electrodes

AbstractThe impending energy crisis entails sustainable battery technologies with improved energy density, reliability, safety and lifetime. Hence, it is essential to gain detailed insights into the surface reactions, ionic diffusion, structural and morphological evolution, and degradation mechanisms of battery electrodes. Recently, X‐ray techniques emerged as revolutionary tools to reveal an in‐depth understanding of the battery during operations. This review provides an overview of the use of in situ/operando X‐ray techniques to understand the different functionalities of electrode materials inside the battery. It will focus on the phase transformation, structural evolution and dynamic properties of the battery electrodes, and discuss the relationship between battery failure and electro‐chemo‐mechanical failure in the electrode. Finally, the limitations of these methods are also discussed with the prospects for effective use of these techniques in the development of advanced battery technologies.

Физико-химические трансформации сапонитсодержащего материала при его активации измельчением

Structural-phase transformations on the surface of powder systems of saponite-containing material after mechanical dispersion have been studied. The degree of crystallinity, adsorption capacity and specific surface energy depending on the time mode of grinding were used as compared information characteristics. It has been established that, despite the fact of the constancy of the degree of crystallinity, mechanical grinding of saponite-containing raw materials leads to its activation, which is expressed by a proportional increase in the sorption capacity of the obtained powders, an increase in the concentration of active adsorption centers and the value of the specific free surface energy. An increase in the time of mechanical grinding of a saponite-containing material leads to the production of samples with an increased (compared to the initial material) surface hydrophilicity.

Hollow-cathode plasma deposited vanadium oxide films: Metal precursor influence on growth and material properties

Due to its different polymorphs, including vanadium pentoxide (V2O5) and vanadium dioxide (VO2), the vanadium oxide (VOX) compound is an immensely interesting material with many important applications. While atomic layer deposition (ALD) is among the possible VOX film synthesis methods, literature reports have majorly utilized thermal-ALD, which reveals as-grown amorphous VOX films. Further post-deposition annealing process is needed to crystallize these films. High-temperature crystallization indeed limits the use of low-temperature compatible materials, processes, and substrates. In this work, we report on the low-temperature crystalline VOX film growth in a hollow-cathode plasma-enhanced atomic layer deposition reactor using two different vanadium precursors, tetrakis(ethylmethylamino)vanadium and vanadium(V) oxytriisopropoxide. Oxygen plasmas were used as co-reactants at a substrate temperature of 150 °C. Along with the purpose of investing in the impact of metal precursors on VOX film growth, we also studied Ar-plasma in situ and thermal ex situ annealing to investigate possible structural enhancement and phase transformation. In situ Ar-plasma annealing was performed with 20 s, 20 SCCM Ar-plasma, while post-deposition ex situ annealing was carried out at 500 °C and 0.5 mTorr O2 pressure. In situ ellipsometry was performed to record instant film thickness variation and several ex situ characterizations were performed to extract the optical, structural, and electrical properties of the films. The outcomes of the study confirm that both metal precursors result in as-grown crystalline V2O5 films at 150 °C. On the other hand, post-deposition annealing converted the as-grown crystalline V2O5 film to VO2 film. Finally, we have also successfully confirmed the metal-to-insulator transition property of the annealed VO2 films via temperature-dependent structural and electrical measurements.

Pressure mediated phase transition and dihydrogen bonding formation in trimethylamine borane

Trimethylamine borane as a potential hydrogen storage material was investigated at high pressures up to 35 GPa where its structural stability, phase transformation, bonding and electronic properties were elucidated.