Narrow Results

Compared to organic–inorganic hybrid perovskite solar cells (PSCs), all inorganic CsPbBr₃ perovskite solar cells have higher stability but lower efficiency. Owing to the low solid solubility of CsBr in methyl alcohol, an incomplete first-step reaction with PbBr₂ reaction takes place at room temperature. As a result, a large amount of CsPb₂Br₅ is generated in the final CsPbBr₃ film, which deteriorates the performance of CsPbBr₃ PSCs. Along these lines, in this work, CsCl was added to increase the reaction between CsBr and PbBr₂ in the first step and high-quality CsPbBr₃ films were prepared without CsPb₂Br₅. Our analysis demonstrated that at the optimal CsCl concentration of 6% in CsBr solution, the CsPbBr₃ perovskite solar cells exhibited a power conversion efficiency of 7.33%. The best device retained 98.57% of the power conversion efficiency (PCE) after storing it for 30 days under ambient air condition.

Solubility of tetragonal lysozyme crystal was measured by using two different methods. The solubility measured by using growth rates of the crystal corresponded well to that measured by using change in the concentration of the supernatant of the solution. Our data also corresponded well to the data obtained by Sazaki et al. and Gray et al., while not to those obtained by Howard et al. and Rosenberger et al. The discrepancies are due to the difference in the principles of the methods. We also checked effects of different initial concentrations on the solubility. Contrary to previous reports, the solutions of the different initial concentrations did not reach equilibrium when their concentrations attained to a same value.

Silk films prepared from regenerated silk fibroin are normally stabilized by β-sheet formation through the use of solvents (methanol, water etc.). Herein, we report a new method of preparing water-stable films without a β-sheet conformation from regenerated silk fibroin solutions by incorporating a small amount (0.2 wt%) of multiwalled carbon nanotubes (MWCNTs). To extend the biomaterial utility of silk proteins, forming water-stable silk-based materials with enhanced mechanical properties is essential. Scanning electron microscopy and transmission electron microscopy were used to observe the morphology of the MWCNT-incorporated silk films. The wide-angle X-ray diffraction provided clear evidence of the crystallization of the silk fibroin induced by MWCNT in the composite films without any additional annealing processing. The tensile modulus and strength of the composite films were improved by 108% and 51%, respectively, by the incorporation of 0.2 wt% of MWCNTs, as compared with those of the pure silk films. The method described in this study will provide an alternative means of crystallizing silk fibroin films without using an organic solvent or blending with any other polymers, which may be important in biomedical applications.

Polyamide powders were prepared as the laser sintering materials for the three-dimensional duplication equipment of selective laser sintering process. Though polyamide powders had a similar chemical structure, there were big differences in thermal properties, particle size and distribution, and shape. These variations had a close relation with the processibility of laser sintering. As far as the particle shape approached a spherical shape, the processibility of laser sintering was improved. The particle size distribution also played an important role in the precision of fabrication.

In this study, the cracking behavior in the bulk and the stress-strain responses of partially crystallized Zr-Ti-Cu-Ni-Be bulk metallic glass after surface modification were investigated. The compressive plasticity was found to be dependent on the surface conditions. The plasticity was enhanced significantly by a complete removal of visible surface flaws. The electro-plating of copper on the rough surface also increased the plasticity of Zr base BMG of the present study. The beneficial effect of the electro-plating can be attributed to filling and smoothening effect due to plating and/or the ductilization of the surface, both of which does not favor crack nucleation. We also found the cracking behavior in the bulk different from the surface region. The cracks in the center of the sample were not straight, but wavy, suggesting the cracks were deflected by or attracted to crystalline particles. A high magnification view of a crack revealed small triangular shaped crystals along the crack path.

The crystallization of melt-spun Fe-Pt-B amorphous alloy with a thickness of 20 µm in steady high magnetic field (HMF) was investigated. The intensity of the applied magnetic field is 0-10 T along with the ribbons annealed at temperature ranging from 673 K to 873 K. The direction of the performed magnetic field is perpendicular to the direction of surface velocity of the Cu wheel. The thermal magnetic properties of the samples were obtained by the thermal gravity analyzer with a magnet attached to the outside of the furnace filled with flowing inert gas. The phase transformations of Fe-Pt-B amorphous alloy on heating with and without the steady HMF were studied by X-ray diffractometry together with the melt-spun ribbon. The average grain size of the samples annealed in HMF was about 10 nm calculated from the XRD patterns. The HMF was thought to be effective on the refinement of nanograins which were produced by the crystallization of the amorphous ribbon during the annealing process.

Amorphous materials of the Si-(B)-C-N system have recently attracted considerable interest because of its hardness, low density, durability at extremely high temperature and easy to be prepared from precursor compounds by polymer route. The materials show a great potential to be used in the field of the Thermal Protective System (TPS) for the aircrafts, while the microstructure and chemical configuration are still not clearly revealed due to its complicated covalent character for this multi-component amorphous material. This paper focused on the characterization of polymer derived Si-(B)-C-N amorphous ceramic, various method were employed in order to obtain accurate information about the microstructure, chemical composition, bonding mode of components, such as TEM, EPMA, NMR and FT-IR. SiC crystalline was found existing in the amorphous glass, which indicates the preparation process was achieved accompanied by crystallization of SiC from polymer precursor. The microstructure of the researched material was analyzed and relative accurate chemical composition was obtained on the basis of characterization result, furthermore the covalent character of the amorphous material was deduced according to the characterization results obtained.

By using the reed-vibration mechanical spectroscopy for liquids (RMS-L), we measured the complex Young's modulus of dimethyl phthalate (DP) during a cooling and heating circulation starting from room temperature at about 2 KHz. The results show that there is no crystallization in the cooling supercooled liquid (CSL) of DP, but a crystallization process in the heating supercooled liquid (HSL) after the reverse glass transition. Based on the measured modulus, crystal volume fraction (v) during the HSL crystallization was calculated. Moreover, the Avrami exponent (n) was obtained according to the JJMA equation and v data. In view of n versus temperature and v, the nucleation dynamics was analyzed, and especially, there has already existed saturate nuclei in DP HSL before the crystallization. Furthermore, the authors inferred that the nuclei are induced by the random frozen stress in the glass, but there is no nucleus in CSL. The above results indicated that RMS-L might provide a new way to measure and analyze the crystallization of liquids.

Fe nanoparticles have been investigated by means of molecular dynamics simulation. The nucleation and crystal growth is analyzed through the potential energy and number of different types of atoms. The simulation shows that when the amorphous sample is annealed at 900 K, it is crystallized into bcc phase. We found that as the crystal cluster has a size larger than some critical value, the mean potential energy of different types of atoms decreases in following orders: amorphous-atom → surface-crystal atom → crystal-atom. As a result, the crystal cluster is stable and tends to have a nearly spherical shape. Further, it was shown that small nuclei form frequently in the core and rarely in the surface area. After a long annealing time a cluster expands and reaches the critical radius. Then this cluster grows exponentially with times. The fully crystallized sample consists of the core with crystalline structure and surface shell with amorphous porous structure. The Fe nanoparticle has a number of polymorphs which are stable upon annealing at 300 K. We have analyzed the pair radial distribution function (PRDF) for obtained polymorphs. We found that as the fraction of crystal-atoms is less than 0.18, the PRDF is like those of amorphous metal. However, the left sub-peak is higher than right sub-peak when the fraction of crystal-atoms is less than 0.05.

In this paper, the effect of minor element addition on the initial structural evolution during crystallization in a simple binary Cu–Zr bulk metallic glass (BMG) forming liquid has been investigated by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Despite no changes in the completely crystallized products, the remarkable opposite impacts on the supercooled liquid region (SLR) and crystallization reaction rate constant $K_{\mathrm{\text{cr}}}$ are observed as a result of minor selective additions of an affine element, i.e., Sn and an immiscible element, i.e., Nb into the Cu–Zr BMG alloy, respectively. Furthermore, it is demonstrated that the primary devitrification pathway and crystalline phases are simultaneously modified, which leads to significant changes in kinetics of atomic rearrangement and thus thermal stability of this material. Such a finding offers a promising way to control the type of primary crystalline phases of BMG-forming metallic supercooled liquids to synthesize novel BMGs or BMG matrix composites for structural or functional applications.

The calcination process was used to remove free carbon and to change the structure of amorphous microsilica powder. The results show that the carbon content in amorphous silica powder strongly depends on the calcination temperature. When the calcination temperature is higher than 900${}^{\circ }$C, the free carbon content, SiO₂ content and weight loss of microsilica powder tend to be stable, with values of 0.05%, 83.8% and 4.8%, respectively. The crystalline structure, particle size and morphology start changing at a calcination temperature of 850${}^{\circ }$C. When the calcination temperature is higher than 900${}^{\circ }$C, the amorphous microsilica powder is fully crystallized. The morphology of the silica fume kept its original spherical shape under 850${}^{\circ }$C, while above 850${}^{\circ }$C the microsilica powder recrystallizes. These results provide a basis for chemical removal of metal impurities in the preparation of high-purity silica powder.

The effect of long-term room temperature ageing on structure and thermal stability of as-cast and inhomogeneously deformed Pd${}_{40}$Ni${}_{40}$P${}_{20}$ metallic glass has been investigated. It is found that the first crystallization peak temperature decreases and this indicates that the thermal stability decreases after ageing for these as-cast and inhomogeneously deformed metallic glass samples. The high density of shear bands formed after deformation disappears and nanocrystallization has been observed after ageing for the inhomogeneously deformed Pd${}_{40}$Ni${}_{40}$P${}_{20}$ metallic glass.

In this paper, crystallization pathway and dynamical heterogeneity (DH) in iron nanoparticle (NP) have been investigated in detail for spherical samples containing 5000 atoms, which were obtained by the molecular dynamics simulation based on Pak–Doyama potential. The crystallization was analyzed through pair radial distribution function, angle distribution, parameter $〈$F${}_{\mathrm{\text{bcc}}}〉$ and transition to different x-types, where x is the bcc, fcc-hcp, ico, 14 or 12. We found that transitions to bcc-type do not happen arbitrarily at any location in NP, but instead they are concentrated in a nonequilibrium region. The crystallization pathway comprises of intermediate states between amorphous and crystalline ones. At the early stage, a large cluster of Cryst-atom formed is located in a middle layer of NP. Then, this cluster grows up and the parameter $〈$F${}_{\mathrm{\text{bcc}}}〉$ for it increases rapidly. At the final stage, the cluster of Cryst-atom is located in a well-equilibrium region covering a major part of NP. It is found that the structure of amorphous and crystalline NPs is strongly heterogeneous and consists of separate regions with different local microstructure. This indicates the DH in NP. We also found that there is a connection between local structures and DH in NP.

Transmittance self-oscillation discovered in amorphous GeSe₂ films has attracted considerable interest, while its underlying mechanism remains controversial. We suggest that the oscillation is governed by at least two kinds of changes; one occurs in absorption for thin ($\sim 6\mu$m) films and the other in refractive-index for thick ($\sim 1$mm) plates. We also detail a model, which assumes recoverable micro-crystallization. An idea for increasing the oscillation frequency is proposed for possible applications.

Some efficient methods have been developed to chemically prepare some magnesium salt products with multiscale morphologies such as MgCO₃·3H₂O and 5Mg(OH)₂·MgSO₄·2H₂O whiskers, Mg₅(CO₃)₄(OH)₂·4H₂O microplates and aggregates, and Mg(OH)₂ plates and spheres. The crystallization processes of the as-prepared products were studied by designing different reaction routes and corresponding growth morphologies. In these solution chemical systems, Mg²⁺ cation was found to be easily coordinated by various ligands, and can be easily transformed into various compounds with variable compositions. The current crystallization observations of some magnesium salts can be readily simulated by the chemical bonding theory of single crystal growth. These results can guide the further studies of various magnesium salts with controllable morphologies.

Crystallization of amorphous SiCN matrix of carbon fiber reinforced SiCN matrix composite (C/SiCN) under vacuum and tensile creep stress was investigated. The phase and microstructure evolution of amorphous SiCN matrix were examined by X-ray diffraction and transmission electron microscopy, respectively. The crystallization behavior of the as-received and 1900°C-annealed C/SiCN during tensile creep test conducted at 1500°C was analyzed. The results indicate that crystallization takes place after annealing at 1900°C for 0.5 h, and the phases formed are β-SiC and α-SiC. Decomposition of amorphous SiCN produces gaseous species such as SiO and CO, and vapor reaction between them and carbon induces SiC nucleation. Local atomic (Si-, C-, N-) rearrangement due to SiCN degradation also yields a large number of Si-C-enriched regions which gradually induces SiC nucleation. The annealing treatment of C/SiCN shows stabilization effect to some extent on the SiCN matrix, but is not sufficient to get a thorough stable phase.

Corrosion resistance of nanocrystalline Fe_73.5Si_13.5B₉Nb₃Cu₁ alloy was investigated and compared to its amorphous counterpart. Low-temperature crystallization occurred during the annealing of amorphous tapes was used to obtain a nanocrystalline structure. The influence of annealing condition on the structure and corrosion resistance of the alloy in NaCl and H₂SO₄ solutions was investigated. Based on the testing results, it was found that nanocrystalline tapes have higher corrosion resistance than amorphous counterpart and H₂SO₄ can promote the occurrence of corrosion compared with NaCl.

Using molecular dynamics simulation, we have studied the structural evolution of FeB nanoparticle under annealing and the physical properties of its polymorphs such as crystalline, amorphous and mixed samples. The main focus of present work is the crystallization mechanism and the local structure of polymorphs of FeB nanoparticle. The simulation result shows that the amorphous sample undergoes the crystallization via the nucleation mechanism. During the crystallization, B atoms move out the places where the Fe crystal locates, and diffuse to the boundary region of Fe crystal. The crystal growth proceeds when this boundary region attains specific properties which are defined by the fraction of B atoms and the energies of AB-atoms and CB-atoms. Further our study indicates that unlike amorphous sample, the crystalline and mixed samples consist of three distinct parts including Fe crystalline and two FeB amorphous parts (B-poor and B-rich amorphous part). The different polymorphs of FeB nanoparticle differ in the local structure, size of Fe crystal and energies of different type atoms.

The crystallization and magnetic behavior of yttrium iron garnet (YIG) prepared by metallo-organic decomposition (MOD) method are discussed. The chemistry and physics related to synthesis of iron and yttrium carboxylates based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found which elucidates synthesis of metallo-organic precursor of YIG in spite of the literatures of doped YIG samples such as Bi-YIG. Typically, the metal carboxylates used in preparation of ceramic oxide materials are 2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and solubility of yttrium and iron 2EH used in synthesis of YIG powder by MOD are reported. The crystallization and magnetic parameters, including saturation magnetization and coercivity of these samples, smoothly change as a function of the annealing temperature. It is observed that high sintering temperature of $1300^{\circ }\mathrm{\text{C}}$ to $1400^{\circ }\mathrm{\text{C}}$ promotes the diffraction peaks of YIG, therefore, we can conclude that the formation of YIG in MOD method increases the crystallization temperature. The maximum value of saturation magnetization and minimum value of coercivity and remanence are observed for the sample sintered at $1200^{\circ }\mathrm{\text{C}}$ which are 13.7 emu/g, 10.38 Oe and 1.5 emu/g, respectively. This study cites the drawbacks in chemical synthesis of metallo-organic-based YIG production.

This paper is devoted to the study of mathematical problems arising in the modelling of nonisothermal polymer crystallization under industrial conditions. A review of the hybrid stochastic-deterministic modelling procedure, which yields an averaged model,^5,8 is given and supplied by the study of mathematical problems arising from it.

Furthermore, multiple scale effects in the crystallization process are studied using different scalings, focussing either on the heat conduction or on the crystallization part. It is shown that in the limit of fast nucleation and slow growth, the model is equivalent to a direct extension of the classical Avrami–Kolmogorov model equations.

In addition, numerical simulations are presented to illustrate the behavior during crystallization. Finally, open questions from mathematical and engineering view points are discussed.