Stabilizing lithium plating in polymer electrolytes by concentration-polarization-induced phase transformation
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36 MATERIALS SCIENCE↗
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Results for “Phase Transformation”
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Ferroic characterizations, phase transformation, and internal bias field in 0.75Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}–0.25PbTiO{sub 3} multiferroic ceramic
The complex perovskite of 0.75Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}–0.25PbTiO{sub 3} (0.75PFW-0.25PT) ceramic was prepared by the conventional oxide mixing method. The detailed microstructure of 0.75PFW-0.25PT ceramic was investigated. At room temperature, the TEM analysis reveals that only cubic structure (nonpolar) exists, which is different from the phase coexistence of cubic (66%) and tetragonal (34%) structure revealed by XRD. A mechanism dominated by a temperature rise due to electron-beam irradiation has been proposed. The XPS measurement confirms the mixed balance state of Fe{sup 2+} and Fe{sup 3+} in the as-prepared 0.75PFW-0.25PT specimen, which facilitates the formation of the defect dipoles with oxygen vacancies, in turn resulting in the internal-bias field (E{sub i}) phenomenon. The appearance of weak magnetic interactions is believed relating to the presence of noncompensated magnetic moments in Fe-rich islands. These results provide key information for understanding the composition, defect, ferroelectric, and ferromagnetic properties in 0.75PFW-0.25PT ceramic.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
The In Situ Observation of Phase Transformations During Intercritical Annealing of a Medium Manganese Advanced High Strength Steel by High Energy X-Ray Diffraction
Microstructural changes during thermal processing of a medium manganese steel containing (in wt%) 0.19C and 4.39 Mn were evaluated in situ with a high energy X-ray diffraction system (HEXRD). Samples with an initial fully martensitic microstructure were heated to intercritical annealing (IA) temperatures of 600 or 650°C, held for 30 min, and cooled to room temperature. Diffraction data were analyzed to determine the variations in austenite and ferrite phase fractions and phase lattice constants throughout the ICA cycles. On heating, the 2 vol. pct of austenite present in the starting microstructure decomposed, and cementite precipitation then occurred. During isothermal holding, the austenite fraction increased, up to 20% for the sample annealed at 650°C. The measured austenite fractions were less than those calculated by Thermo-Calc for equilibrium conditions, indicating that the 30-min hold time was insufficient to achieve near-equilibrium conditions. Observed changes in lattice parameters during isothermal holding were interpreted to reflect composition changes due to redistribution of the C and Mn between austenite and ferrite. The results are discussed in relation to the potential for controlling austenite stability during ambient temperature deformation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Reversible Hydrogen-Induced Phase Transformations in La 0.7 Sr 0.3 MnO 3 Thin Films Characterized by In Situ Neutron Reflectometry
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Phase Transformation Enables Stable Cycling and Fast Charging of Cation-Disordered Rocksalt Cathodes
Developing high-capacity, long-life cathodes is critical to overcome the energy limitations of current Li-ion batteries. In this work, we report a Li-excess cation-disordered rocksalt (DRX) cathode, Li 1.167 Mn0.7Ti 0.133 O 1.8 F 0.2 (M 0.7 F 0.2 ), which demonstrates excellent electrochemical performance. This cathode delivers a capacity approaching 250 mAh g –1 and maintains 200 mAh g –1 over 200 cycles with an average discharge voltage of 3.1 V at 2 V cutoff. The formation of a spinel-like phase during cycling enables fast charging, achieving over 240 mAh g –1 at 2C for 100 cycles. Combined X-ray absorption spectroscopy and transmission electron microscopy reveal reversible electrochemical redox processes and stable Mn local structures during 2 V discharge. These results highlight the potential of DRX cathodes for next-generation Li-ion batteries and provide insights into strategies to overcome kinetic limitations and optimize the cathode-electrolyte interface.
25 ENERGY STORAGE↗
High pressure phase transformation in yttrium sulfide(YS): A first principle study
First principles calculations have been carried out to analyze structural, elastic and dynamic stability, of YS under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of compression suggests the B1→B2 transition at ∼ 49 GPa. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state. The single crystal elastic constants derived from the energy strain method agree well with the experimental values. The activation barrier between B1 and B2 phases calculated at transition point is ∼ 17/mRy/formula unit. Our lattice dynamic calculations show that at ambient condition, the B1 phase is lattice dynamically stable and frequencies of phonon modes in different high symmetry directions of Brillouin zone agrees well with experimental values. The B2 phase also is dynamical stable at ambient condition as well as at ∼ 49 GPa, supporting our static lattice calculation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Surface modification induced phase transformation and structure variation on the rapidly solidified recast layer of titanium
In this study, neodymium-doped yttrium orthovanadate (Nd:YVO{sub 4}) as a laser source with different scanning speeds was used on biomedical Ti surface. The microstructural and biological properties of laser-modified samples were investigated by means of optical microscope, electron microscope, X-ray diffraction, surface roughness instrument, contact angle and cell cytotoxicity assay. After laser modification, the rough volcano-like recast layer with micro-/nanoporous structure and wave-like recast layer with nanoporous structure were generated on the surfaces of laser-modified samples, respectively. It was also found out that, an α → (α + rutile-TiO{sub 2}) phase transition occurred on the recast layers of laser-modified samples. The Ti surface becomes hydrophilic at a high speed laser scanning. Moreover, the cell cytotoxicity assay demonstrated that laser-modified samples did not influence the cell adhesion and proliferation behaviors of osteoblast (MG-63) cell. The laser with 50 mm/s scanning speed induced formation of rough volcano-like recast layer accompanied with micro-/nanoporous structure, which can promote cell adhesion and proliferation of MG-63 cell on Ti surface. The results indicated that the laser treatment was a potential technology to enhance the biocompatibility for titanium. - Highlights: • Laser induced the formation of recast layer with micro-/nanoporous structure on Ti. • An α → (α + rutile-TiO{sub 2}) phase transition was observed within the recast layer. • The Ti surface becomes hydrophilic at a high speed laser scanning. • Laser-modified samples exhibit good biocompatibility to osteoblast (MG-63) cell.
36 MATERIALS SCIENCE↗
Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries
Not Available
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Effect of crystal structure and cationic order on phonon modes across ferroelectric phase transformation in Pb(Fe{sub 0.5-x}Sc{sub x}Nb{sub 0.5})O{sub 3} bulk ceramics
Pb(Fe{sub 0.5-x}Sc{sub x}Nb{sub 0.5})O{sub 3} [(PFSN) (0 ≤ x ≤ 0.5)] multiferroic relaxors were synthesized and the temperature dependence of phonon modes across ferroelectric to paraelectric transition was studied. With varying Sc content from x = 0 to 0.25 the structure remains monoclinic and with further addition (x = 0.3 - 0.5) the structure transforms into rhombohedral symmetry. Structural refinement studies showed that the change in crystal structure from monoclinic to rhombohedral symmetry involves a volume increment of 34-36%. Associated changes in the tolerance factor (1.024 ≤ t ≤ 0.976) and bond angles were observed. Structure assisted B′-B″ cation ordering was confirmed through the superlattice reflections in selected area electron diffraction (SAED) pattern of Pb(Sc{sub 0.5}Nb{sub 0.5})O{sub 3} (x = 0.5). Cation ordering is also evident from the evolution of Pb-O phonon mode in Raman spectra of compositions with rhombohedral symmetry (x ≥ 0.3). The high temperature Raman scattering studies show that the B-localized mode [F{sub 1u}, ∼250 cm{sup −1}] and BO{sub 6} octahedral rotational mode [F{sub 1g}, ∼200 cm{sup −1}], both originating from polar nano regions (PNRs) behave like coupled phonon modes in rhombohedral symmetry. However, in monoclinic symmetry they behave independently across the transition. Softening of B localized mode across the transition followed by the hardening for all compositions confirms the diffusive nature of the ferroelectric transformation. The presence of correlation between the B localized and BO{sub 6} rotational modes introduces a weak relaxor feature for systems with rhombohedral symmetry in PFSN ceramics, which was confirmed from the macroscopic dielectric studies.
36 MATERIALS SCIENCE↗
Cr incorporated phase transformation in Y 2 O 3 under ion irradiation
Under irradiation, chemical species can redistribute in ways not expected from equilibrium behavior. In oxide-dispersed ferritic alloys, the phenomenon of irradiation-induced Cr redistribution at the metal/oxide interfaces has drawn recent attention. Here, the thermal and irradiation stability of the FeCr/Y 2 O 3 interface has been systematically studied. Trilayer thin films of 90 nm Fe - 20 at.% Cr (1 st layer)/100 nm Y 2 O 3 (2 nd layer)/135 nm Fe - 20 at.% Cr (3 rd layer) were deposited on MgO substrates at 500 °C. After irradiation, Cr diffuses towards and enriches the FeCr/Y 2 O 3 interface. Further, correlated with Cr redistributed into the oxide, an amorphous layer is generated at the interface. In the Y 2 O 3 layer, the original cubic phase is observed to transform to the monoclinic phase after irradiation. Meanwhile, nanosized voids, with relatively larger size at interfaces, are also observed in the oxide layer. First-principles calculations reveal that Cr substitution of Y interstitials in Y 2 O 3 containing excess Y interstitials is favored and the irradiation-induced monoclinic phase enhances this process. Lastly, our findings provide new insights that may aid in the development of irradiation resistant oxide-dispersed ferritic alloys.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Phase transformations during the Ag-In plating and bonding of vertical diode elements of multijunction solar cells
The conditions of the bonding of silicon multijunction solar cells with vertical p-n junctions using Ag-In solder are studied. The compositions of electrodeposited indium films on silicon wafers silver plated by screen printing and silver and indium films fabricated by layer-by-layer electrochemical deposition onto the surface of silicon vertical diode cells silver plated in vacuum are studied. Studying the electrochemical-deposition conditions, structure, and surface morphology of the grown layers showed that guaranteed bonding is provided by 8-min heat treatment at 400 Degree-Sign C under the pressure of a stack of metallized silicon wafers; however, the ratio of the indium and silver layer thicknesses should not exceed 1: 3. As this condition is satisfied, the solder after wafer bonding has the InAg{sub 3} structure (or InAg{sub 3} with an Ag phase admixture), due to which the junction melting point exceeds 700 Degree-Sign C, which guarantees the functioning of such solar cells under concentrated illumination.
36 MATERIALS SCIENCE↗
Residual stress induced crystalline to amorphous phase transformation in Nb{sub 2}O{sub 5} quantum dots
Nb{sub 2}O{sub 5} quantum dots (QDs) were grown using a simple technique of vacuum thermal evaporation. QDs were found to be crystalline in nature by selected area electron diffraction (SAED) in TEM. Samples with thickness up to 20 nm did not show any significant residual strain. Residual stress effect on band gap of crystalline Nb{sub 2}O{sub 5} was studied for films thicker than 20 nm. Residual strain was determined using SAED of the films with reference to powder X-ray diffraction (XRD). Films thicker than 45 nm become amorphous as analyzed by both SAED and XRD. The optical absorption of films in the range 25–60 nm indicates significantly varying optical band gap of films. The varying band gap with film thickness scales linearly very well with the variation of residual stress with film thickness. The residual stress dependence of band gap of crystalline films yields stress free band gap as 3.37 eV with pressure coefficient of band gap (∂E{sub g}/∂P){sub T} = −29.3 meV/GPa. From this study, the crystalline to amorphous transformation in tetragonal form of M-Nb{sub 2}O{sub 5} has been determined to be at about 14 GPa. Both pressure coefficient of band gap and crystalline to amorphous transition for tetragonal M-Nb{sub 2}O{sub 5} have been determined for the first time in the literature.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Elasticity of two-dimensional ferroelectrics across their paraelectric phase transformation
The mechanical behavior of two-dimensional (2D) materials across 2D phase changes is unknown, and the finite temperature (T) elasticity of paradigmatic SnSe monolayers—ferroelectric 2D materials turning paraelectric as their unit cell turns from a rectangle into a square—is described here in a progressive manner. To begin with, their zero–T total energy landscape gives way to (Boltzmann-like) averages from which the elastic behavior is determined. Furthermore, these estimates are complemented with results from the strain-fluctuation method, which employs the energy landscape or ab initio molecular dynamics data. All approaches capture the coalescence of elastic moduli < C 11 (T) > = < C 22 (T) > due to the structural transformation. The broad evolution and sudden changes of elastic parameters < C 11 (T) >, < C 22 (T) >, and < C 12 (T) > of these atomically thin phase-change membranes establishes a heretofore overlooked connection among 2D materials and soft matter.
2-dimensional systems↗
Phase transformations in multiferroic Bi{sub 1−x}La{sub x}Fe{sub 1−y}Ti{sub y}O{sub 3} ceramics probed by temperature dependent Raman scattering
Optical phonons and phase transitions of Bi{sub 1−x}La{sub x}Fe{sub 1−y}Ti{sub y}O{sub 3} (BLFTO, 0.02 ≤ x ≤ 0.12, 0.01 ≤ y ≤ 0.08) ceramics have been investigated by Raman scattering in the temperature range from 80 to 680 K. Four phase transitions around 140, 205, 570, and 640 K can be observed. The Raman modes are sensitive to the spin reorientation around 140 and 205 K, owing to the strong magnon-phonon coupling. The transformation around 570 K is a structural transition from rhombohedral to orthorhombic phase due to an external pressure induced by the chemical substitution. The anomalies of the phonon frequencies near Néel temperature T{sub N} have been discussed in the light of the multiferroicity. Moreover, it was found that the structural transition temperature and T{sub N} of BLFTO ceramics decrease towards room temperature with increasing doping composition as a result of size mismatch between substitution and host cations.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Substructural-Phase Transformations during Heat Treatments of the Ti–50.9 at % Ni Nanocrystalline Alloy
The method of transmission electron microscopy is used to study the grain-subgrain structure of the Ti–50.9 at % Ni nanocrystalline alloy after heat treatments at 300–500°C. It is found that the decomposition of the B{sub 2} solid solution of TiNi by the heterogeneous mechanism occurs in the subgrain structure, while the Ti{sub 3}Ni{sub 4} particles are not observed in nanograins. The features of the recovery and recrystallization of the alloy and their relationship with the processes of dissolution and precipitation of Ti{sub 3}Ni{sub 4} particles are revealed.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Structural and Phase Transformations in Superlocalization Band in Ni{sub 3}Ge Single Crystal
The paper studies the high-temperature plastic deformation in Ni{sub 3}Ge alloy single crystals localizing in a band a few tens of microns wide that reaches the shear strain of thousands of percent. The electron backscatter diffraction and synchrotron radiation techniques allow investigating the structure of the single crystal in the band of super-localized plastic deformation. It is shown that super-localization of plastic deformation occurs due to the formation of polycrystalline multi-level substructure in the initial single crystal. The grain size and grain misorientation bimodal distributions are determined in the polycrystalline substructure. Also, regions of amorphous state are observed in the super-localization band at high homologous temperature Т > 0.5T{sub m}. A partial destruction of the far atomic order is detected.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Study of phase transformation and microstructure of alcohol washed titania nanoparticles for thermal stability
Nanostructured titania have been successfully synthesized by hydrolysis of alkoxide at calcination temperatures 500 °C, 600 °C and 700 °C. As the calcination temperature increases, alcohol washed samples show lesser rutile content as compared to water washed samples. Morphology and Particle sizes was determined by field emission scanning electron microscopy (FESEM), while thermogravimetric-differential scanning calorimetry (TG-DSC) was used to determine thermal stability. Alcohol washed samples undergo 30% weight loss whereas 16% in water washed samples was observed. The mean particle sizes were found to be increase from 37 nm to 100.9 nm and 35.3 nm to 55.2 nm for water and alcohol washed samples respectively. Hydrolysis of alkoxide was shown to be an effective means to prepare thermally stable titania by using alcohol washed samples as a precursor.
36 MATERIALS SCIENCE↗
Melt-driven mechanochemical phase transformations in moderately exothermic powder mixtures
Typically, mechanochemical reactions between solid phases are either gradual (by deformation-induced mixing), or self-propagating (by exothermic chemical reaction). In this work, by means of a systematic kinetic analysis of the Bi–Te system reacting to Bi 2 Te 3 , we establish a third possibility: if one or more of the powder reactants has a low melting point and low thermal effusivity, it is possible that local melting can occur from deformation-induced heating. The presence of hot liquid then triggers chemical mixing locally. The molten events are constrained to individual particles, making them distinct from self-propagating reactions, and occur much faster than conventional gradual reactions. We demonstrate that the mechanism is applicable to a broad variety of materials systems, many of which have important functional properties. This mechanistic picture provides a new perspective as compared to conventional, gradual mechanochemical synthesis, where thermal effects are generally ignored.
36 MATERIALS SCIENCE↗