Lattice Transformation Research Articles

Influence of chlorite treatment on the fine structure of alkali pretreated sugarcane bagasse

Bagasse, an industrial agro waste is treated with alkali initially to remove hemicelluloses fraction followed by treatment with sodium chlorite solution varying the treatment time. The novelty of the work lies in the bleaching with chlorite treatment in alkaline medium. The treated bagasse fiber was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), particle size analysis by dynamic light scattering technique (DLS), optical microscope, scanning electron microscope (SEM), atomic force microscope (AFM), UV spectroscope, and thermogravimetric analysis (TGA). It was found that during alkali treatment, a lattice transformation from cellulose I to cellulose II took place. Chlorite treatment removed lignin initially, and then with increasing time, the amorphous portion of cellulose is removed, rendering high crystallinity in the fiber. All the changes have been accounted by evaluation of LOI (lateral order of index), TCI (total crystallinity index), and HBI (hydrogen bond intensity) from FTIR study. XRD study also revealed the same fact. AFM study also supported the same fact indicating generation of sharp crystal and rough surface. Morphological study of treated and untreated bagasse fiber also exhibited fibrillation of fiber. Radius of hydration as estimated by DLS analysis followed a decreasing trend with increase in chlorite treatment time. The loss of transparency in cellulose fiber has been exposed by UV spectra analysis. TGA study showed that thermal stability has been increased with chlorite treatment. Such alkali treatment along with sodium chlorite for cellulose extraction from bagasse has not been performed by earlier investigators. Extracted cellulose fiber will be a very suitable reinforcing agent due to highly fibrillated morphology.

Evolution of crystal structure in high-entropy AlCoCrFeNi alloy: An in situ high-temperature X-ray diffraction study

A powder of uniform high entropy alloy AlCoCrFeNi was produced by relatively short-term (90 min) mechanical alloying in a planetary mill followed by annealing at 873, 1073 and 1273 K for 5.5 h. Results of high-temperature in situ XRD analyses demonstrated the occurrence of specific crystal lattice transformations taking place in major fcc and bcc phases during annealing and cooling down. Shrinkage of atomic structures was detected for all phases after annealing at any temperature, while precipitation of the σ-phase occurred only at 1073 K. A drift of the (111) peak relative to the (200) peak of the fcc phase at 1273 K allowed us to assume the occurrence of weak martensitic transformations: a high-temperature cubic phase turns into slightly tetragonal phase (a/c = 1.00426) upon cooling down to room temperature. This transformation takes place without mechanical stress or deformation. Despite structural transformations, the major high-entropy phases remained after annealing.

Interdependent Linear Complexion Structure and Dislocation Mechanics in Fe-Ni

Using large-scale atomistic simulations, dislocation mechanics in the presence of linear complexions are investigated in an Fe-Ni alloy, where the complexions appear as nanoparticle arrays along edge dislocation lines. When mechanical shear stress is applied to drive dislocation motion, a strong pinning effect is observed where the defects are restricted by their own linear complexion structures. This pinning effect becomes weaker after the first dislocation break-away event, leading to a stress-strain curve with a profound initial yield point, similar to the static strain aging behavior observed experimentally for Fe-Mn alloys with the same type of linear complexions. The existence of such a response can be explained by local diffusion-less and lattice distortive transformations corresponding to L10-to-B2 phase transitions within the linear complexion nanoparticles. As such, an interdependence between a linear complexion structure and dislocation mechanics is found.

Particle-size dependent structural transformation of skyrmion lattice

Magnetic skyrmion is a topologically protected particle-like object in magnetic materials, appearing as a nanometric swirling spin texture. The size and shape of skyrmion particles can be flexibly controlled by external stimuli, which suggests unique features of their crystallization and lattice transformation process. Here, we investigated the detailed mechanism of structural transition of skyrmion lattice (SkL) in a prototype chiral cubic magnet Cu2OSeO3, by combining resonant soft X-ray scattering (RSXS) experiment and micromagnetic simulation. This compound is found to undergo a triangular-to-square lattice transformation of metastable skyrmions by sweeping magnetic field (B). Our simulation suggests that the symmetry change of metastable SkL is mainly triggered by the B-induced modification of skyrmion core diameter and associated energy cost at the skyrmion-skyrmion interface region. Such internal deformation of skyrmion particle has further been confirmed by probing the higher harmonics in the RSXS pattern. These results demonstrate that the size/shape degree of freedom of skyrmion particle is an important factor to determine their stable lattice form, revealing the exotic manner of phase transition process for topological soliton ensembles in the non-equilibrium condition.

A Ni-free β-Ti alloy with large and stable room temperature super-elasticity

A Ni-free β-Ti alloy comprising Ti-40Hf-13Nb-4.5Sn (wt.%) was developed as a substitute for NiTi (nitinol) alloys in medical applications. It is found that, due to significant Stress Induced Martensite (SIM) transformation and large lattice transformation strain, combined with good strength and stability, this alloy showed large and stable super-elastic deformation behavior at room temperature. Total recoverable strain of 5.3 % was obtained at 6% deformation. According to preliminary data, mechanical properties and fatigue performance of this alloy are within the neighborhood of super-elastic NiTi alloys. Plateau strengths can be further tuned to a wide range by low temperature aging similar to Ni-rich binary NiTi. It can be manufactured in large industrial scales by commercial production lines, has been melted in hundreds of kilogram scale, and is relatively easy to shape set into device subcomponent forms. With additional characteristics such as relatively high X-ray visibility, good corrosion resistance and biocompatibility, this alloy provides a superelastic option in Ni-sensitive dental, orthodontic, orthopedic bone staple, and neurovascular applications to name a few possibilities.

Noble Metal Nanomaterials with Nontraditional Crystal Structures

Noble metals (Ru, Os, Rh, Ir, Pd, Pt, Ag, and Au) are known for their extraordinary oxidant-resistant behavior, good electrical and thermal conductivity, high work function, and brilliant luster. All occur in close-packed crystal structures: Ru and Os in hexagonal close-packed (hcp) and the rest in face-centered cubic (fcc) structures, both possessing high-symmetry structures and, therefore, a high degree of stabilization. Numerous studies in the literature have attempted to stabilize these metals away from their conventional crystal structures with the aim of realizing new properties. While obtaining conventional fcc metals in hcp structure or vice versa has been the subject of most studies, there are also examples of fcc metals crystallizing in lower-symmetry structures such as monoclinic. The nonnative crystal structures are generally realized during the crystallite growth itself, with a few exceptions in which a posttreatment was required for lattice transformation. In most cases, the new crystal structures pertain to the nanometer-length scale in the form of nanoparticles, nanoplates, nanoribbons, and nanowires, but there are good examples from microcrystallites as well. In this article, we review this active area of research, focusing on ambient stable crystal systems with some account of their interesting properties as reported in recent literature.

Sm-induced multifunctionality and poling effect on luminescence of Sm-doped (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 piezoceramics

The lead-free multifunctional ceramics Sm3+-doped (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 were synthesized via conventional sintering. The influences of Sm3+ concentration on phase structure, grain size, Curie temperature, ferro-/piezoelectric properties, as well as photoluminescence (PL) performances of the ceramics have been investigated. The results show that with the Sm3+ concentration of 0.4[Formula: see text]mol%, the integrated optoelectronic performances are best. In order to further study the relationship between ferroelectric and PL features, the poling effect on PL intensities of the ceramics has been focused on, giving the highest enhancement factors of 52.6% induced by both lattice distortion and phase transformation. The electric poling is an effective route to enhance the PL performance of luminescent ferroelectrics.

Niobium doping of Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with enhanced structural stability and electrochemical performance

Lithium-rich layered oxides with high energy density have been intensively investigated as advanced lithium-ion batteries cathode materials. However, capacity degradation and voltage decay caused by irreversible lattice oxygen loss and structural transformation during cycling restrict their application. Herein, we proposed a high valance cations Nb5+ doping strategy and synthesized a series of Li1.2Mn0.54-x/3Ni0.13-x/3Co0.13-x/3NbxO2 (x = 0, 0.01, 0.02 and 0.03) cathode materials. The effects of Nb5+ doping on crystallographic structure and electrochemical property were systematically studied. In virtue of the large ionic radii and strengthened Nb–O bonds, the doped samples present commendable structural stability and expanded interlayer spacing for Li-ions migration, which ensures the upgraded cyclic stability and rate performance. In particular, the electrode with x = 0.02 delivers a discharge specific capacity of 265.8 mAh g-1 at 0.2 C with decelerated voltage decay, while 86.9% capacity are remained after long-term cycles. Moreover, excellent discharge specific capacity of 153.4 mAh g−1 is still attained at 5 C accompanied with enhanced Li-ion diffusion kinetics.

Effects of Ar ion irradiation in an ICP discharge on the titanium surface topology

VT1-0 (Russian equivalent of Grade 2) titanium surfaces were modified under argon ion bombardment from the low-pressure inductively coupled plasma (ICP). The ion processing allowed us to prepare various types of structures on titanium with controlled characteristic dimensions at nano- and miscroscale (from tens of nm to 3 µm). The hillock, porous, conical, wall/cell structures as well as their combinations have been obtained. The topology type and the characteristic dimensions of surface features depend on the current density js, Ar ion energy Ei, irradiation fluence Φ (or processing time t), and the sample temperature T during the treatment. The microstructures appear on the surface provided the titanium sample is irradiated at temperatures below 900 °C. The sample temperature was determined by both the average current density (jsav from 0.2 to 20 mA/cm2) and the ion energy (Ei from 150 to 1500 eV). A certain fluence is required for uniform surface coverage with microstructures. We suppose that the titanium surface texturing is a result of a complex interplay of the following mechanisms: sputtering, re-sputtering (shadowing), crystal lattice transformation, accumulation and annihilation of defects, and hypothetically, argon retention.

Braiding Ultrathin Au Nanowires into Ropes.

Braiding is a common skill in daily life but rare at the nanoscale. Most of the current nanohelices are directly grown or assembled without involving mechanical interactions, and they are thus distinctively different from ropes in terms of functions and mechanisms. Here, by coaxially twisting multiple ultrathin Au nanowires, nanoropes are synthesized with elegant helical patterns that are consistent with the macroscopic equivalents. The strain relaxation of lattice transformation causes the nanowires to pursue the maximum degree of twisting, while the mutual packing interactions in a bundle prevent sideways emergence of U-turns. The consistent chirality of the seemingly independent strands can only arise when a first twisting strand causes morphological deformation in its neighbors, which induces the collective uni-directional twisting. The spontaneous braiding and the "remote" control of the nanowires involve mechanical interactions and possibly energy transmission, thus opening doors to chiral assembly and future smart nanodevices.

Tracking Metamorphic Dehydration Reactions in Real Time with Transmission Small- and Wide-Angle Synchrotron X-ray Scattering: the Case of Gypsum Dehydration

AbstractWe present a review of a unique non-destructive method for the real-time monitoring of phase transformations and nano-pore evolution in dehydrating rocks: transmission small- and wide-angle synchrotron X-ray scattering (SAXS/WAXS). It is shown how SAXS/WAXS can be applied to investigating rock samples dehydrated in a purpose-built loading cell that allows the coeval application of high temperature, axial confinement, and fluid pressure or flow to the specimen. Because synchrotron sources deliver extremely bright monochromatic X-rays across a wide energy spectrum, they enable the in situ examination of confined rock samples with thicknesses of ≤ 1 mm at a time resolution of order seconds. Hence, fast kinetics with reaction completion times of about hundreds of seconds can be tracked. With beam sizes of order tens to hundreds of micrometres, it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres, thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly. Therefore, the SAXS/WAXS method offers the opportunity to acquire data on a striking range of length scales: for rock samples with thicknesses of ≤ 10-3 m and widths of 10-2 m, a lateral interrogation-point spacing of ≥ 10-5 m can be achieved. Within each irradiated interrogation-point volume, information concerning pores with sizes between 10-9 and 10-7 m and the crystal lattice on the scale of 10-10 m is acquired in real time. This article presents a summary of the physical principles underpinning transmission X-ray scattering with the aim of providing a guide for the design and interpretation of time-resolved SAXS/WAXS experiments. It is elucidated (1) when and how SAXS data can be used to analyse total porosity, internal surface area, and pore-size distributions in rocks on length scales from ∼1 to 300 nm; (2) how WAXS can be employed to track lattice transformations in situ; and (3) which limitations and complicating factors should be considered during experimental design, data analysis, and interpretation. To illustrate the key capabilities of the SAXS/WAXS method, we present a series of dehydration experiments on a well-studied natural gypsum rock: Volterra alabaster. Our results demonstrate that SAXS/WAXS is excellently suited for the in situ tracking of dehydration kinetics and the associated evolution of nano-pores. The phase transformation from gypsum to bassanite is correlated directly with nano-void growth on length scales between 1 and 11 nm for the first time. A comparison of the SAXS/WAXS kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature. It is anticipated that the SAXS/WAXS method combined with in situ loading cells will constitute an invaluable tool in the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively.

Phase transformation and mechanical properties of Ti-(10–30)Zr–3Mo–1Sn alloys

Studies on three Ti–xZr–3Mo–1Sn (x=10–30 at.%) alloys found that the influences of Zr on phase transformation and mechanical properties are closely tied to its effect on β-phase stability. It decreases the β-transus by ~8.8 °C/at.%, suppresses the formation of α-phase or martensite during cooling and enhances the room temperature super-elasticity. The influence of Zr on lattice transformation strain is weak with the calculated maximum transformation strains of ~8% in all three alloys regardless of their large differences in Zr content. The largest recoverable strain of ~3.8% was obtained in alloy 30Zr after heat treatment at 600 °C. Heat treating at 600 °C produces a α+β dual phase structure with unique texture patterns in alloys 10Zr and 20Zr. Although texture patterns of α and β phases can be understood based on their crystal orientation relationship, mechanisms that caused these textures remain unknown. Aging at 200 °C for a short time increases the super-elastic strain without sacrificing material ductility and total recoverable strain.

Predictive micromechanical model for plastic accommodation and crystallography of martensite embryo

It is widely accepted that the lattice transformation strain and plastic shearing of a martensite embryo preset its final lattice orientation. However, the phenomenological theory of martensite crystallography (PTMC) solves an inverse problem where accommodative slip or twinning systems leading to certain structures are sought among a lot of admitted candidates. This approach explaining the known result still cannot unambiguously predict the latter or, moreover, its dependence on the transformation conditions. In order to avoid uncertainty of PTMC, a micromechanical model is formulated that directly follows a natural sequence of the transformation strain and plastic accommodation. With slip systems uniquely selected in this way at habit planes {111}γ and {557}γ, corresponding orientation relationships are predicted and then verified by relevant data on low carbon lath martensite.

Laser nitridation on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

To give a deep insight into the nitrogen transfer mechanism during laser solid-state surface modification on titanium alloy, laser nitridation was conducted on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy (TC11) without melting the metal surface. Microstructure characterizations of nitride layer formed under solid state condition were detailedly explored and the formation process of TiN phase was carefully discussed based on the lattice transformation. Results indicate that the nitride layer forming within a few seconds is composed of TiN phase layer and α phase layer with an orientation relationship: (11¯1)TiN // (0001)α, [011]TiN // [211¯0]α. Formation of TiN phase experiences fast solid-state transformation from α phase. Phase transformation from α-Ti lattice to TiN lattice experiences orthorhombic lattice transformation due to the shear deformation caused by rapid interstitial solution of nitrogen. After repeated laser nitridation process upon three times, nitride layer was thickened with an improved hardness of 824 HV. Linearly reciprocating ball-on-plane wear tests indicate that wear resistance of laser nitridation samples could be enhanced by a factor of 13.

Comment on "Tunable thermal quenching properties of Na3Sc2(PO4)3:Eu2+ phosphors tailored by phase transformation details" by Z. Liu et al., Dalton Trans., 2020, 49, 3615.

Liu et al. (Dalton Trans., 2020, 49, 3615-3621) reported that emission of the Na3Sc2(PO4)3:Eu2+ phosphor showed tunable thermal quenching properties which were ascribed to the thermal event associated with polymorphic phase transformations. In this comment, I argue that the abnormal negative thermal quenching of the Na3Sc2(PO4)3:Eu2+ phosphor could be a pitfall caused by a diminishment in the optical path lengths of the spectrofluorometer originating from a continuous increase in the volume of the phosphor due to lattice thermal expansion and phase transformation at elevated temperatures.

Phase field modeling of deformation twinning in β-metastable titanium alloys

A multi-phase field model describing the anisotropic growth of the {332}<113> twinning system in β-metastable titanium alloys is hereby presented considering the geometrically linear and non-linear frameworks. Phase fields are associated with each twin variant of the {332}<113> system. The lattice transformation describing the twinning systems is incorporated in the model via relevant eigenstrain tensors. We illustrate the capability of our model by investigating the formation of twins networks, within both geometrically linear and non linear frameworks. In particular, it is shown that the predicted microstructures exhibit strong differences, resulting from a difference in the selection of the variant habit planes.

Stochastic Differential Scanning Calorimetry by Nonlinear Optical Microscopy.

Stochastic phase transformations within individual crystalline particles were recorded by integration of second harmonic generation (SHG) imaging with differential scanning calorimetry (DSC). The SHG activity of a crystal is highly sensitive to the specific molecular packing arrangement within a noncentrosymmetric lattice, providing access to information otherwise unavailable by conventional imaging approaches. Consequently, lattice transformations associated with dehydration/desolvation events were readily observed by SHG imaging and directly correlated to the phase transformations detected by the DSC measurements. Following studies of a model system (urea), stochastic differential scanning calorimetry (SDSC) was performed on trehalose dihydrate, which has a more complex phase behavior. From these measurements, SDSC revealed a broad diversity of single-particle thermal trajectories and direct evidence of a "cold phase transformation" process not observable by the DSC measurements alone.

Elastodynamic behavior of mechanical cloaks designed by direct lattice transformations

Steering waves in elastic solids is more demanding than steering waves in electromagnetism or acoustics. As a result, designing material distributions which are the counterpart of optical invisibility cloaks in elasticity poses a major challenge. Waves of all polarizations should be guided around an obstacle to emerge on the downstream side as though no obstacle were there. Recently, we have introduced the direct-lattice-transformation approach. This simple and explicit construction procedure led to extremely good cloaking results in the static case. Here, we transfer this approach to the dynamic case, i.e., to elastic waves or phonons. We demonstrate broadband reduction of scattering, with best suppressions exceeding a factor of five when using cubic coordinate transformations instead of linear ones. To reliably and quantitatively test these cloaks efficiency, we use an effective-medium approach.

Customized unique core-shell Fe2N@N-doped carbon with tunable void space for microwave response

Here, we report a unique core-shell nanocomposite of Fe2N@N-doped carbon that coats dopamine-derived carbon shells on porous Fe2N nanoparticles via a facile and effective soft chemical method. The feasibility of preparing core-shell structure in the process of polymerization is realized by utilizing the fact that affluent amino and hydroxyl groups in dopamine endow the formidable chelation ability with metal ions. Temperature-dependent volume shrinkage effect of Fe2N originates from the lattice transformation in nitridation process, which is the key factor to control the void space inside carbon nanocubes and optimize the electromagnetic performance. Consequently, the as-prepared samples achieve excellent reflection loss (RL) values and effective absorption bandwidth at an even thin thickness of 1.4 mm. The balance between the temperature-dependent conduction loss and the optimization of hole structure impedance matching may be responsible for the excellent microwave behaviors. This work offers an attractive core-shell Fe2N@carbon with controllable void space as a promising candidate to handle the electromagnetic interface (EMI) issues.

Effect of second-phase particles evolution and lattice transformations while ultrafine graining and annealing on the corrosion resistance and electrical conductivity of Al–Mn–Si alloy

Al–Mn–Si specimens were subjected to constrained groove pressing, cold-rolling and annealing, respectively. Microstructure characterizations indicated that second-phase particles were arranged along the material flow direction and did not orient at grain boundaries. Analysis of x-ray diffraction patterns exhibited that severe straining led to dynamic restoration and lattice swelling. Since findings for annealed specimens did not follow a linear trend; however, they were in good agreement with corrosion characteristics and electrical conductivity results. Outputs of electrochemical polarization test revealed that corrosion rate has direct correlation with lattice distortion and dislocation density measurements. As most of the particles have not remarkable open circuit potential with aluminum matrix along with other existent particles and also did not contain required size to act as origin of pitting corrosion, they would capable of forming the passive layer porous and subsequently could prevent encouraging uniform passive layer. In the case, they let the aggressive ions to penetrate beneath the passive layer and react with talented sites like dislocations and grain boundaries. Scrutiny of lattice d-spacing proved that by imposing deformation, electrical conductivity alters by change in d-spacing since by annealing at elevated temperature conductivity follows the winner of competition between d-spacing, lattice distortion and particles transformations.