Initial Stage Of Crystallization Research Articles

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 3 – Cluster growth and crystal nucleation

This Part 3 focuses on the detailed study of the nanostructures forming in amorphous microwires which were previously received and described in the Part 2. The clustering process was studied at long-term DC Joule heating’s much lower the crystallization temperature. Particular attention is paid to the study of the redistribution of the components of the initial stage of crystallization. The studies were carried out using the Atom Probe Tomography method (APT), which allows for the identification of individually considered atoms. A description and analysis of APT data processing techniques are provided for studying the cluster structure and distribution of elements in the amorphous matrix and crystalline phases. To identify crystalline phases, data obtained using High-Resolution Transmission Electron Microscopy (HR-TEM) and Scanning Transmission Electron Microscopy (STEM), as well as X-Ray Powder Diffraction (XRPD) with synchrotron radiation source were used. The applied techniques made it possible to establish that the formation of nuclei of crystalline phases is preceded by three stages of the amorphous microwire matrix evolution. At the first stage, clusters of the first and second coordination spheres appear. At the second stage, the clusters coagulate and become more than 2 nm in diameter, the stage ends with the predominance of Co-rich and silicide Me-Si clusters. At the third stage, they grow to an average diameter of 4.5 nm, the predominance of clusters of this type remains, and the formation of nuclei of crystalline phases α-Co and Co2Si, with a size of about 8 nm, occurs. This stage is characterized by high stable soft magnetic properties. With a further increase in the heat treatment temperature, a gradual deterioration of the soft magnetic properties and further structural transformation occur – structures of joint crystalline phases from two crystalline phases α-Co and Co2Si are formed in the amorphous matrix, and crystallization occurs with the alternation of these two phases. This leads to a significant redistribution of alloy components. As a result, an amorphous barrier layer is formed in the amorphous matrix near the surface of the growing two-phase substructures, enriched in chromium and silicon; this layer affects the growth of crystalline phases, slowing it down.

The Lac à l'Orignal phosphate deposit and constraints on high-quality phosphatic ore in massif-type anorthosite, Grenville Province, Canada

Phosphate is an indispensable component in the fertilizer industry. It has recently become a critical part of the green energy transition because of the demand for lithium ferro phosphate in rechargeable batteries. A significant amount of phosphate ore (∼90 %) is globally produced from sedimentary rocks. High-quality phosphate ore containing low amounts of toxic elements, however, is mostly produced from igneous carbonatite.The Lac à l'Orignal deposit (∼1069–993 Ma), Canada, in the central Grenville Province, contains a large amount of fluorapatite (≤ 20 %) hosted in oxide-bearing norite-gabbronorite-anorthosite layered intrusions. The deposit is hosted in the Vanel Anorthosite (1080 ± 2 Ma) near the northern border of the Mattawa Anorthosite (1016 ± 2 Ma). The major host rock oxide-apatite-gabbronorite (OAGN) is primarily composed of plagioclase, orthopyroxene, clinopyroxene, fluorapatite, ilmenite, and magnetite. The Al contents of the OAGN orthopyroxene indicate that the magmatic deposit was emplaced at mid-low crustal levels (∼2.0–3.6 kbar) and reverse zoning in the OAGN plagioclase suggests <2.5 kbar of pressure change during their crystallization. An overall increase of REE + Y concentrations in the OAGN fluorapatite with decreasing their fluorapatite contents indicates that the magma went through fractional crystallization. This study suggests that high abundances (ca. > 8 %) of fluorapatite in some OAGN were produced from crystal avalanching after initial crystal settling. Antithetic correlation between the Cl content of fluorapatite and the Mg# [Mg/(Mg + Fe2+)] of coexisting orthopyroxene suggests that phosphate ores with low Cl contents are expected for OAGN that formed at the initial stages of magma crystallization. Therefore, the Mg# of the OAGN orthopyroxene provides an exploration tool for targeting phosphate ore with low Cl content, which is preferred in the production of phosphoric acid, a major intermediate feedstock for the fertilizer and green energy industries. Apatite contents in carbonatite and average P2O5 content in carbonatite melt are generally similar to those of the Lac à l'Orignal OAGN. The average concentrations of REE, and toxic metals, such as Pb, Th, and U, in the OAGN fluorapatite are, however, lower than those in apatite from carbonatite worldwide. Therefore, the apatite of the OAGN appears to be of high quality and more environmentally-friendly as a source of phosphate ore.

Cd-Free Pure Sulfide Kesterite Cu2 ZnSnS4 Solar Cell with Over 800mV Open-Circuit Voltage Enabled by Phase Evolution Intervention.

The Cd-free Cu2 ZnSnS4 (CZTS) solar cell is an ideal candidate for producing low-cost clean energy through green materials owing to its inherent environmental friendliness and earth abundance. Nevertheless, sulfide CZTS has long suffered from severe open-circuit voltage (VOC ) deficits, limiting the full exploitation of performance potential and further progress. Here, an effective strategy is proposed to alleviate the nonradiative VOC loss by manipulating the phase evolution during the critical kesterite phase formation stage. With a Ge cap layer on the precursor, premature CZTS grain formation is suppressed at low temperatures, leading to fewer nucleation centers at the initial crystallization stage. Consequently, the CZTS grain formation and crystallization are deferred to high temperatures, resulting in enhanced grain interior quality and less unfavorable grain boundaries in the final film. As a result, a champion efficiency of 10.7% for Cd-free CZTS solar cells with remarkably high VOC beyond 800mV (63.2% Schockley-Queisser limit) is realized, indicating that nonradiative recombination is effectively inhibited. This strategy may advance other compound semiconductors seeking high-quality crystallization.

Piezoelectric, mechanical, and crystallographic properties of polyvinylidene fluoride‐hexafluoropropylene based composites reinforced by different dimensional carbon nanomaterials

AbstractPolymer based piezoelectric materials are increasingly used because of their lightweight and flexibility. To understand the effects of different dimensional carbon nanomaterials on the properties of polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) based composites, carbon black (CB), carbon nanotube (CNT), and few‐layer graphene (FLG) were used to reinforce PVDF‐HFP for preparing different composites, respectively. Their piezoelectric, mechanical, and crystallographic properties were tested. The results show that CB/PVDF‐HFP composite film has the best piezoelectric property, successively followed by FLG/PVDF‐HFP and CNT/PVDF‐HFP at 0.5%, 0.05%, and 0.1% contents of CB, FLG, and CNT, respectively. In the initial crystallization stage, CB better plays the best role of crystallization core, increasing the electroactive crystalline phase content and crystallization rate. The appropriate contents of CNT and FLG promote the formation of β crystalline phase. In the polarization stage, CB forms a uniform nonconductive network in the composite film and shows the best polarization effect. CNT tends to form connections and has the worst polarization effect. FLG forms a “microcapacitor” structure to enhance the local polarization effect. The effects of CB, CNT, and FLG on crystalline phase changes and piezoelectric property enhancements of PVDF‐HFP based composites are mainly due to their differences in size, morphology, and quantity.Highlights Effects of CB, CNT, and FLG on the piezoelectricity of PVDF‐HFP are investigated; CB more obviously increases the piezoelectricity of PVDF‐HFP than CNT and FLG; α, β, and γ crystalline phase changes in PVDF‐HFP based composites are understood; CB forms smaller and more uniform crystal cores in PVDF‐HFP than CNT and FLG; CB markedly increases the contents of electroactive crystalline phases in PVDF‐HFP.

Crystallization kinetics and mechanical property of yttrium-modified Zr-Cu-Ag-Al bulk metallic glasses

The bulk metallic glasses of two different compositions i.e. Zr44Cu40Al8Ag8 and Zr44Cu40Al8Ag7Y1 were prepared by copper mold casting technique in this study. As-cast microstructure both BMG’s found to completely amorphous as depicted by X-ray diffraction and transmission electron microscopy. The differential scanning calorimetry (DSC) results reveal that Y-addition leads to an increase in the nucleation rate at the initial stages of crystallization but imposes resistance to the growth of the crystalline phases at later stages. Furthermore, the Y-addition results in better creep resistance for Zr44Cu40Al8Ag7Y1 glassy alloy at room temperature.

Desupersaturation dynamics in solutions with applications to bovine and porcine insulin crystallization

Evolution of crystal ensembles in supersaturated solutions is studied at the initial and intermediate stages of bulk crystallization. An integro-differential model includes fluctuations in crystal growth rates, initial crystal-size distribution and arbitrary nucleation and growth kinetics of crystals. Two methods based on variables separation and saddle-point technique for constructing a complete analytical solution to this model are considered. Exact parametric solutions based on these methods are derived. Desupersaturation dynamics is in good agreement with the experimental data for bovine and porcine insulin. The method based on variables separation has a strong physical limitation on exponentially decaying initial distribution and leads to the distribution function increasing with time. The method based on saddle-point technique leads to a dome-shaped crystal-size distribution function decreasing with time and has no strong physical limitations. The latter circumstance makes this method more reasonable for describing the kinetics of bulk crystallization in solutions and melts.

Eutectic crystallization and melting in sharp concentration gradients.

The initial stages of contact melting and eutectic crystallization in sharp concentration gradients between two crystalline components are studied and simulated analytically and numerically. Contact melting is shown to become possible only after the formation of some critical width of solid solutions. Crystallization in the sharp concentration gradient may lead to the formation of periodic structures in the interface vicinity. In addition, at least for the eutectic systems of Ag-Cu type, the threshold temperature should exist, under which the "precipitation + growth" mechanism of crystallization may be changed to "polymorphic crystallization with eutectic composition + subsequent spinodal decomposition."

In situ study of chiral symmetry breaking in sodium chlorate solutions by Mueller matrix polarimetry.

This work presents a novel approach for investigating symmetry-breaking processes during crystallization using Mueller matrix polarimetry. By applying this method to the cooling process of NaClO3 solutions, we demonstrate its ability to capture not only the initial and final stages of crystallization but also the intermediate steps and dynamics of the process. This technique provides more comprehensive information and insights into the symmetry-breaking mechanisms involved in crystal formation. Overall, this study highlights the potential of Mueller matrix polarimetry for in situ statistical measurements of the optical rotation and for monitoring the evolution of enantiomeric excesses.

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 2 – Microstructural evolution and electrical resistivity change during DC Joule heating

This Part 2 focuses on the processes of atomic regions ordering of the amorphous material and continues study of the processes occurring in Part 1. The formation of pre-crystals / clusters and nanocrystallization of Co-based amorphous microwires during DC Joule heating were investigated, as well as the influence of these processes on the electrical resistance of the samples and the effect of giant magnetoimpedance (GMI). In this paper we investigated the dependence of the change in the maximum response of the GMI diagonal component at different temperatures and holding times in the DC Joule heating process, and discuss the effect of the ductile-brittle transition on the electrical resistance and the GMI effect. Using high-resolution transmission electron microscopy (HR-TEM) and the inverse Fourier transform technique, it was shown that at long exposure during the DC Joule heating, significantly below the crystallization temperature (~ 400 °C), the formation and growth of pre-crystals / clusters occur in various sizes (1 – 8 nm) and shapes. At the initial stage of crystallization, the microwire has three distinct regions of the clusters and nanocrystals formation (surface, pre-surface, and bulk). Moreover, pre-crystals / clusters growth and further bulk formation of nanocrystals (of 10 nm and more) leads to a sharp drop in the electrical resistance and degradation of the GMI microwire diagonal component response. The approach of controlled long-term holding during the DC Joule heating applied in the study allows for creation of various nanoscale structures in an amorphous matrix and provides an opportunity to grow of a given structure in amorphous alloys.

Crystallization evolution behavior of amorphous Fe85.7Si7.9B3.6Cr2C0.8 powder produced by a novel atomization process

Fe-Si-B amorphous alloy has the advantages of excellent soft magnetic properties, low magnetic loss, stable DC bias performance and strong corrosion resistance, etc. It is one of the commonly used raw materials for high-end electronic and electrical components. In this study, the thermodynamics and kinetics of the crystallization transition of high magnetic induction amorphous powder Fe85.7Si7.9B3.6Cr2C0.8 produced by a novel atomization process were investigated experimentally under non-isothermal and isothermal conditions based on DSC and XRD. The results show that the high Si contents in the amorphous composition and the eutectic reaction during initial crystallization stage lead to a structural transition between the ordered Fe-Si phases A2(α-Fe(Si)), B2(FeSi) and DO3(Fe3Si), thus resulting in the third exothermic peak of crystallization in the DSC curve of this system. In addition, the first exothermic peak of crystallization corresponding to the eutectic reaction is analyzed in detail in this paper. The crystallization process of the amorphous material is as follows: (a) Amorphous; (b) Amorphous+Fe3B+α-Fe(Si)+Fe3Si+Fe5Si3+FeSi; (c) Amorphous+ Fe3B+Fe2B+α-Fe(Si)+Fe3Si+Fe5Si3+FeSi; (d) Fe2B+α-Fe(Si)+Fe3Si+Fe5Si3+FeSi; (e) Fe2B+α-Fe(Si)+Fe3Si+Fe5Si3. And the undercooled liquid region of the amorphous powder is 52 K, the activation energy of glass transition is 396.73 kJ·mol−1, the activation energy of the first crystallization peak is 292.64 kJ·mol−1, and the fragility value is 27 belongs to strong metallic glass system. It also suggests that the amorphous materials have good thermal stability and glass forming ability (GFA).

Isothermal and Non-Isothermal Crystallization Kinetics of Poly(ethylene chlorotrifluoroethylene).

The isothermal (IT) and non-isothermal (NIT) crystallization kinetics, morphology, and structure of poly(ethylene chlorotrifluoroethylene) (ECTFE) were investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (XRD). The Avrami equation could well describe the overall IT crystallization process of ECTFE, and, furthermore, the overall crystallization rate decreased at higher crystallization temperatures (Tc). The equilibrium melting point for ECTFE was found to be 238.66 °C. The activation energies for IT and NIT crystallization were determined as −137.68 and −120.54 kJ/mol, respectively. The Jeziorny model fitted well with the initial stages of NIT melt crystallization, while deviations from linearity in the later stages of the process were due to the collisions of spherulites. Spherulites of ECTFE organized in a hexagonal crystal system were found. The relative crystalline degree of ECTFE under NIT conditions was about 54.55%, and this decreased with the increase in cooling rate. Moreover, the Ozawa and Mo models were suitable for modeling the overall NIT crystallization process of ECTFE.

Molecular dynamics simulation of impurity effects near the NaCl interface during the initial rapid stages of growth

For salt processing, it is necessary to understand impurity incorporation into NaCl crystals at the molecular level. In this study, molecular dynamics (MD) simulations of NaCl crystal growth were performed to analyze the solution structure near the interface between a NaCl crystal and NaCl–NaBr or NaCl–NaI solutions and to calculate the dehydration energy in the presence of impurities (Br− and I−). Furthermore, the adsorption mechanism of solute ions onto the NaCl surface during the initial growth stage of batch crystallization was investigated. Both Br− and I− were found to decrease the adsorption rate, but the impurity effects of these ions were different. Moreover, the adsorption rate in the presence of Br− was faster than that in the presence of I−. In the presence of Br−, the adsorption rate was decreased by the rate-limiting effect of the growth rate of Br−. By contrast, in the presence of I−, the adsorption rate was reduced by the abundance of I− near the interface, as the supply of Cl− near the interface was limited by electrostatic effects. In addition, the local concentration of impurities (Br− and I−) near the crystal–solution interface was higher than the saturated concentration. This difference from the bulk composition suggests that impurities may even crystallize at unsaturated concentrations.

Mold temperature- and molar mass-dependent structural formation in micro-injection molding of isotactic polypropylene

The structural formation and development of isotactic polypropylene (iPP) upon the micro-injection molding process was investigated at different mold temperatures and molecular weights utilizing a real-time synchrotron radiation small angle X-ray scattering (SAXS) technique combined with a customized micro-injection molding apparatus. Shish-kebab structure and parent-daughter lamellae were found to be formed during micro-injection molding for all iPP samples. In the case of kebab lamellae, a considerable growth in the long period and in the average thickness of lamellar crystallites and amorphous domains is observed at initial stages of crystallization for samples molded at varying temperatures. This effect is caused by the successive formation of thin lamellae in the outer layer and thick lamellae in the inner layer during the manufacturing process as evidenced by the spatial distribution of the crystalline lamellae across the thickness. In addition, the length of the shish formation increases remarkably at the onset of crystallization, the extent of which is dependent on the mold temperature. Despite the large changes of the lamellar stacks and the shish misorientation, the final length of the shish remains essentially unchanged when varying mold temperature. Since there is a critical orientation molecular weight above which the chains are stretched and oriented to form stable shish, the iPP sample with a low molar mass exhibits an overall decrease in the scattering intensity of SAXS patterns compared to the high molecular weight polypropylene. • The structural formation of iPP is investigated utilizing a customized micro-injection molding device. • Shish-kebab and parent-daughter lamellae are formed during micro-injection molding. • A considerable increase in the long period is observed at initial stages of crystallization. • The length of the shish formation increases remarkably at the onset of crystallization. • The final shish length remains essentially unchanged when varying mold temperature.

Multifunctional Heterocyclic-Based Spacer Cation for Efficient and Stable 2D/3D Perovskite Solar Cells.

Two-dimensional/three-dimensional (2D/3D) Ruddlesden-Popper perovskite materials have shown the enormous potential to achieve both efficient and stable photovoltaic devices for commercial applications. Unfortunately, the single function of spacer cations limits their further improvements in efficiency to reach values as high as those of 3D perovskites. Herein, we developed a new-type multifunctional heterocyclic-based spacer cation of 2-(methylthio)-4,5-dihydro-1H-imidazole (MTIm+) to achieve a synchronous improvement of efficiency and stability for 2D/3D perovskite solar cells (PSCs). Owing to the presence of special chemical groups (imidazole and methylthio), strong interactions have been found between MTIm+ and the 3D perovskite component, leading to an excellent passivation effect. More important, at the initial stage of crystallization, uniform nucleation distribution would be generated around the spacer cation, which is helpful for improved crystallinity and reduced growth defects. The smaller layer space compared to that of cations based on aromatic hydrocarbons caused effective carrier transfer between inorganic layers in 2D/3D perovskites. As a result, the 2D/3D (n = 30) PSCs based on MTIm exhibit a champion PCE up to 21.25% with a high Voc of 1.14 V. Besides, the 2D/3D perovskite devices have realized dramatically enhanced humidity and thermal stability, maintaining 94% of the starting PCE enduring aging at about 50% RH for 2880 h and at 85 °C for 360 h, respectively. We believe that it would provide a significant strategy to further promote the photovoltaic performances and the long-term stability of 2D/3D perovskite devices toward future practical applications.

Mechanical Behavior of Fe- and Co-Based Amorphous Alloys after Thermal Action

The effect of heat treatment on the structure and mechanical properties of Co-Fe-Cr-Si-B/Fe-Cr-B/Fe-Ni-B amorphous alloys has been studied systematically. Melt-quenching (spinning method) was used for production of investigated amorphous alloys. The transmission electron microscopy (TEM) was used to study the structure transformations. The effect of temperature on deformation behavior (plasticity, microhardness, crack resistance, and the density and average length of shear bands) of the amorphous alloys was studied by bending and microindentation. It is shown that the ductile–brittle transition, which occurs at the stage of structure relaxation in amorphous alloys, is caused by two factors: a decrease in the susceptibility of the amorphous matrix to plastic flow and an abrupt decrease in the resistance to the development of quasibrittle cracks. It is established that the transition to a two-phase amorphous–nanocrystalline state upon annealing leads to substantial strengthening of the alloys and a partial recovery of their plasticity. It is proved that the strengthening of amorphous alloys at the initial stages of crystallization can be initiated by the difference in the elastic moduli of the amorphous matrix and the precipitated nanocrystals, as well as by the specific features of the interaction between nanocrystalline phase particles and shear bands propagating under external actions. It is established that the phenomenon of plasticization in amorphous alloys (the crack resistance can increase after annealing in a certain temperature range) is due to the effective retardation of cracks on nanoparticles.

Research progress in Zr-Ti containing high-entropymatellic glasses

<p indent="0mm">High-entropy bulk metallic glasses (HE-BMGs) are alloys that contain five or more principal elements in equal or near-equal atomic ratios. HE-BMGs have the composition of a high-entropy alloy (HEA), structure of a bulk metallic glass, and satisfy the thermodynamic, kinetic, and structural conditions for amorphous formation. They have excellent comprehensive properties and potential as structural and functional materials. This paper summarizes the composition design, crystallization behaviors and the physical, mechanical, and thermal stability properties of Zr-Ti containing HE-BMGs. The phase formation rules for HEAs can be used to determine compositions region for bulk glass formation. However, the developed HE-BMGs have poor glass-forming ability (GFA) compared with other BMGs in the same system. In order to obtain HE-BMGs with high GFA, attempts have been made to design near-equiatomic HE-BMGs. An effective strategy for developing HE-BMGs with high GFA is to replace elements in the HE-BMGs at equal atomic ratios. This strategy has enabled the preparation of a Ti₂₀Zr₂₀Hf₂₀Be(Cu_7.5Ni_12.5) high-entropy amorphous alloy with a critical diameter of <sc>30 mm.</sc> New near-equiatomic HE-BMGs with high GFA can also be obtained by similar element substitution based on selected ternary alloys. Because of the high-entropy effect, the crystallization behaviors of HE-BMGs differ from those of other BMGs in the same/similar alloy systems. The non-isothermal crystallization of Zr-Ti containing HE-BMGs involves multistage crystallization, and the nucleation rate decreases with increasing crystallization degree. Zr-Ti containing HE-BMGs have higher activation energies than Vit-1, which means better thermodynamic stabilities. In addition to having a high-entropy effect, near equatomic Zr-Ti containing HE-BMGs are affected by a single principal element. For example, the nucleation rate of Zr₃₁Ti₂₇Be₂₆Cu₁₀Ni₆ increases gradually during the initial stage of crystallization; this is consistent with the behavior of Zr-based metallic glass. At the next stage, high entropy effect plays the major role. In other words, the effect induced by single principal elements has a stronger influence on the crystallization process of the near equiatomic Zr-Ti containing HE-BMGs. In terms of mechanical properties, a Zr-Ti containing HE-BMG has high strength, i.e., close to the theoretical prediction, high corrosion and wear resistance, and room-temperature brittleness. The room-temperature plasticity of the Zr-Ti containing HE-BMGs can be obviously improved by adjusting the composition, surface coating, cryogenic cycling treatment and cryothermal cycling treatment. Because of the high-entropy effects and sluggish diffusion effect due to the complexity of the ingredients, HE-BMGs have high creep resistance and corrosion resistance and give high thermal oxidation performances. The macroscopic deformation behaviors of the HE-BMGs show significant temperature and strain rate dependence. At the temperature of hot-embossing process, it was found that Zr-Ti containing HE-BMGs possess a relatively poor thermoplastic formability, especially under the reduced mould size to tens micrometers. Ultrasonic loading is an effective measure to conspicuously enhance the thermoplastic formability of Zr-Ti containing HE-BMGs. There are some expected goals that have not been reached in research on Zr-Ti containing HE-BMGs. At present, the alloy design strategies are mainly applicable to single-element, binary and ternary amorphous alloys. Multi-principal-element amorphous alloys have no appropriate measures for design. The compatibility of tensile ductility and high strength of HE-BMGs is still an overarching goal. New techniques such as machine learning and high throughput can be used to identify compositions with excellent properties. With the development and use of new experimental apparatus, the influence of a higher number of elements on the structures and properties of Zr-Ti HE-BMGs will able to be verified more accurately. In terms of hot-embossing process, the problem of the high viscosities of Zr-Ti HE-BMGs at their formation temperature needs to resolve by process optimization.

Manifestation of Initial Crystallization and c-Axis Texture in Pr-Fe-B Magnetic Thin Films Grown on Glass Substrates under Volume Effect

VSM, XRD, SEM, TEM, and EDS measurements were applied to investigate the relationship between the thickness and the structure of Pr-Fe-B layer which initiated and propagated crystallization of the Pr2Fe14B phase at 600 °C on the glass substrate. The magnetic properties of the sputtered Pr-Fe-B film were also investigated in terms of evolution of the Pr2Fe14B hard magnetic phase. The crystallization process was investigated for a range of the thickness of Pr-Fe-B layer from 25 to 125 nm. The thin film structure at the 50 nm thickness showed the initial crystalline characteristics of hard magnetic Pr2Fe14B phase, the fine signal of c-axis orientation, perpendicular magnetic anisotropy (PMA), and coercivity (Hc). SEM and TEM results revealed the blossom of surface morphology and the ordered layer structure of thin films, respectively. EDS result showed various concentration of the main magnetic elements occurred at the initial stage of crystallization. The growth of the Pr2Fe14B phase was supported by a new Fe3Si underlayer. The thin film containing non-uniform crystal grains and two-phase microstructure showed the coupling exchange appeared between the hard magnetic and soft magnetic phases. The magnetization properties (Hc, PMA) was strongly affected by the Si3N4 underlayer and glass substrate. Magnetic analysis suggests that a high-efficiency Pr-Fe-B thin film is made of a fine microstructure.

Excellent soft magnetic properties in Co-based amorphous alloys after heat treatment at temperatures near the crystallization onset

The effect of heat treatment of Co-based amorphous microwires at temperatures near the crystallization (Tcr) onset on micromagnetic structure, magnetostriction, and magnetoimpedance (MI) was investigated. As the annealing temperature approaches Tcr, the hysteresis loops abruptly change the shape from almost rectangular to inclined with a small coercivity and remanence magnetization. This behavior is quite unique since even partial crystallization deteriorates soft magnetic properties. The Kerr-microscopy confirmed the formation of a fine circular domain structure and an easy anisotropy direction of a helical type. Both current and furnace annealing with appropriate high temperatures produce similar magnetic transformation. The origin of the formed easy anisotropy is different from that induced by current annealing at temperatures below the Curie temperature and is associated with a change in the magnetostriction constant, which drops from positive to negative values. This could be explained by structural relaxation leading to amorphous phase decomposition at the very initial stage of crystallization. The effect is not specific for the Co-rich alloy composition and was observed in microwires of two compositions: Co71Fe5B11Si10Cr3 and Co66.6Fe4.28B11.51Si14.48Ni1.44Mo1.69 which in the as-prepared state have axial and circumferential anisotropies, respectively. The obtained combination of magnetic anisotropy, magnetostriction and temperature stability leads to useful MI properties, in particular, at Gigahertz frequencies.

Evaluation of the Effect of Minor Additions in the Crystallization Path of [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx Metallic Glasses by Means of Mössbauer Spectroscopy

Understanding the crystallization of metallic glasses is fundamental in the design of new alloys with enhanced properties and better glass-formability. The crystallization of a series of Fe-based metallic glasses of composition [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx (M = Mo, Nb and Zr) has been studied by means of differential scanning calorimetry and transmission Mössbauer spectroscopy. This latter technique allows the following of the microstructural evolution of the studied alloys through the identification and quantification of the several Fe-containing crystalline phases and also through the changes in the amorphous structure at the initial stages of crystallization. The results show that the crystallization products are the same for all the studied compositions (α-Fe, Fe2B, (FeCo)23B6 and a paramagnetic remnant) although with different relative proportions and the crystallization of a phase without Fe in the alloys with Zr. Moreover, the addition of Zr favors the crystallization of α-Fe causing a detrimental effect on the glass forming ability, while the increase in Mo content up to 6 at% favors the crystallization of (FeCo)23B6. The different amount of α-Fe and borides is presented as a measure of the glass forming ability of this type of alloys.

The effects of applying an alternating electric field to lysozyme solutions during the initial crystallization stage

This work investigated the effects of applying low frequency and low intensity alternating current (AC) electric fields on the formation of crystals in protein solutions. The uniform electric fields were applied to hen egg white lysozyme (HEWL) with NaCl in the supersaturated region at room temperature. We evaluated the application time and field intensity dependencies on the number and the size of the generated crystals. Only an hour field application reduced the number of the HEWL crystals. The electric-field applying intensity changed the number of the generated crystals non-monotonically, which shows that the application field intensities have some optimum conditions for the protein crystallization.