K0101 結晶性・非晶性材料のディフェクトダイナミクス・シミュレーション(基調講演)

Crystalline mesophases: Structure, mobility, and pharmaceutical properties

The series of static and magic angle spinning NMR experiments were carried out on two zircons of low and moderate α-decay dose. The aim was to identify the nature of the amorphous phase in terms of the local structure around silicon and to quantify the amounts of amorphous and crystalline material for a given α-decay dose. The effects of paramagnetic defects produced during radiation damage were checked to verify that spectra obtained were representative of the majority of Si atoms in the sample. In the moderately dosed sample 77 ± 8% of the total possible Si NMR signal was detected. This was divided into 34±3% amorphous and 66 ± 3% crystalline material. Rapid relaxation delay spectra show that paramagnetic defects exist more or less equally in crystalline and amorphous regions, indicating that the absolute fraction of crystalline and amorphous material is close to these values. The amorphised region has an average peak position of ∽-90ppm characteristic of Q 2 polymerised tetrahedral environments with signal intensity spread over the whole Qn range. An SiO2-like phase was not observed.

Commonly used constitutive laws for crystalline and viscous materials have been compared to predict the densification behavior under hot‐pressing and sinter‐forging. Experimental results, from literature for one loading condition, have been used to extract the constitutive laws for amorphous and crystalline materials and, these in‐turn, have been used to predict behavior under a different set of loading conditions. Ideally, the constitutive parameters obtained from one set of loading conditions and thermal history should apply to a different set of conditions. However, there is a lack of systematic experimental studies in which this can be checked. In this paper, we use constitutive parameters obtained from one set of conditions to predict the densification response under a different set of loading conditions. For both sintering of amorphous and crystalline materials, we use two different constitutive parameters and compare the predictions of these for the case where experimental results are not available. In addition, the effect of temperature on densification behavior for stress‐assisted sintering has been investigated. It is shown that the two commonly used constitutive models for viscous sintering (Scherer and Skorohod–Olevsky) predict similar behavior for amorphous materials. However, for crystalline materials, the predictions of the Riedel–Svoboda and the Kuhn–Sofronis–McMeeking (KSM) models are different. Finally, it is shown that the dependence of the normalized densification on temperature, under constant heating rate conditions, with parameters obtained from isothermal experiments, is a good test for the models.

The effects of various doping materials (amorphous phases: TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , MgO, and C and crystalline phases: HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) on the microstructure and magnetic properties of FePt thin films have been investigated. It is found that FePt films with amorphous doping materials especially MgO and C have better (001) texture and grain isolation than doping with crystalline materials. Nevertheless, doping with crystalline materials, FePt films were preferred to form columnar structures with a larger aspect ratio compared with semi-spherical grain shape for amorphous doping materials. Moreover, all the FePt-X films exhibit better perpendicular anisotropy except for FePt-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films due to some FePt (200) textured films epitaxial grown directly on tetragonal (002) textured ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . For crystalline materials doping, the (001) texture and perpendicular anisotropy could be improved by tuning crystalline oxide materials with appropriate lattice structure, which may offer a method for application in FePt in heat-assisted magnetic recording media.

Structural studies of the NaCaPO 4–SiO 2 sol–gel derived materials

Laser-assisted field evaporation is studied in a large number of compounds, including amorphous and crystalline phase change materials employing atom probe tomography. This study reveals significant differences in field evaporation between amorphous and crystalline phase change materials. High probabilities for multiple events with more than a single ion detected per laser pulse are only found for crystalline phase change materials. The specifics of this unusual field evaporation are unlike any other mechanism shown previously to lead to high probabilities of multiple events. On the contrary, amorphous phase change materials as well as other covalently bonded compounds and metals possess much lower probabilities for multiple events. Hence, laser-assisted field evaporation in amorphous and crystalline phase change materials reveals striking differences in bond rupture. This is indicative for pronounced differences in bonding. These findings imply that the bonding mechanism in crystalline phase change materials differs substantially from conventional bonding mechanisms such as metallic, ionic, and covalent bonding. Instead, the data reported here confirm a recently developed conjecture, namely that metavalent bonding is a novel bonding mechanism besides those mentioned previously.

The influence of implanted hydrogen (up to a concentration level of 3 at. %) on the microstructure of silicon (Si) materials is investigated by Fourier transform infrared spectroscopy as well as by effusion of hydrogen and of (low dose) implanted helium. Three materials of low original hydrogen concentration, crystalline Si, electron beam evaporated amorphous Si, and plasma-deposited hydrogenated amorphous Si (using high deposition temperature) were investigated. Significant differences between crystalline and amorphous materials were observed. In crystalline Si, implanted hydrogen is found to generate multivacancies that trap diffusing helium while this is not the case in amorphous Si. Accordingly, cavities where hydrogen is located in amorphous Si must be smaller than divacancies. Those cavities in amorphous Si, present from the growth process, that trap helium tend to disappear when the implanted hydrogen concentration increases. Annealing of the materials up to temperatures of 575 °C was also studied. No significant change in the density of voids (trapping helium) occur but in case of crystalline Si the bonding sites of hydrogen as well as the diffusion paths of helium change.

Up to 47 mass% of gadolinium can be dissolved in a baseline borosilicate glass (mol%) 20 B2O3, 5 A12O3, 60 SiO2, and 20 Na2O. Understanding the dissolution of Gd in borosilicate melts is important in the optimization of glass formulations. However, probing amorphous materials with spectroscopic techniques is challenging research when little knowledge of the local chemical environment of the glass network is available. Electron energy loss fine structure (ELFS) spectroscopy is one available technique that has several advantages for probing the local structure of amorphous materials. This technique gives local atomic structure information equally well for both amorphous and crystalline materials. There is high sensitivity for low Z elements like boron, oxygen, aluminum, and silicon whereas x-ray absorption fine structure (XAFS) technique faces experimental difficulties. Hence, results from ELFS can be complimentary to the results from XAFS. For medium to high Z elements, one can use the L- or M-edges of the elemental spectrum.

The magnetic after effect has been considered as an effective tool for the investigation of structural defects in crystalline materials. However, the increasing use of the amorphous ferromagnetic materials, because of their wide range of possible applications, created interest in the study of these materials and the same technique is now being applied for amorphous materials. In the present work, measurements of the magnetic properties have been made made on amorphous material with composition Fe40 Ni40 B20 using a differential AC method . Measurements have been made from 4.2 to 750 K. The material for the specimens was produced by melt-spinning technique and was in the form of ribbon, 2mm wide and 25µm thick. The whole experimental run was controlled by a BBC micro-computer. The results obtained are discussed and compared with the previous work.

Two effects should be considered when keV photons suffer elastic scattering: the scattering of photons by the bound electrons of a free atom, named Rayleigh scattering and if, besides the Rayleigh scattering, the scattering due to different atoms gives rise to interference phenomena. The interatomic and intermolecular cooperative effects which modify the free-atom coherent scattering process are well know for highly ordered structures such as crystalline materials but are important for amorphous solids and liquids where short-range ordering occurs. Amorphous materials but are important for amorphous solids and liquids where short- range ordering occurs. Amorphous materials do not give such well-defined scatter conditions, but they do still give diffraction patterns which is characteristic of the particular materia. The availability of a very intense and highly collimated synchrotron radiation beam makes possible to study scattering properties of different amorphous materials. These materials were chosen because they intend to simulate the physical properties of body tissues and human bone. All measurements, were performed at the x-ray diffraction beamline of the Laboratorio Nacional de Luz Sincrotron, in Campinas, Brazil. The x-ray diffraction measurements were carried out with an 11.101 keV x-ray beam and included data from 1 equals 0.39 to q equals 4.13 per nm.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The mechanoresponsive behavior and photochemical response of a new bis(cyanostyryl)benzene fluorophore (CSB-5) were investigated. Green fluorescence with λem,max of 507 nm was found for CSB-5 in chloroform solution, mirroring the behavior of a previously reported similar dye (CSB-6). Alternatively, crystalline samples of CSB-5 exhibited orange fluorescence with λem,max of 620 nm, attributable to excimer emission. Although the emission color change was not clearly noticeable by naked eye, CSB-5 exhibited mechanochromic luminescence, due to transformation into the amorphous state upon grinding the crystalline powder. Interestingly, rubbed films of CSB-5 prepared on glass substrates exhibited a pronounced emission color change from orange to green when exposed to UV light. This response is the result of a photochemical reaction that occurs in the amorphous state and which causes a decrease of the excimer emission sites so that the emission color changes from excimer to monomer. The crystalline material did not display such a photoinduced emission color change and the difference in photochemical reactivity between crystalline and amorphous states was exploited to pattern the emission color of rubbed films.

The crystallization of amorphous drugs during dissolution is a type of solution mediated phase transformation that can reduce the bioavailability enhancement one hoped to gain from the amorphous state. The goal of this study was to explore the effects of processing on the dissolution performance of amorphous indomethacin. The amorphous solids were prepared by four techniques, quench cooling the melted solid, cryogrinding γ indomethacin amorphous for 1 or 3 h and quench cooling the solid followed by 1 h of cryogrinding. Dissolution results assessed in a flow-through intrinsic dissolution apparatus reveal decreases in the dissolution rate of amorphous indomethacin during the experimental time frame indicating that a solution mediated phase transformation has occurred. The amorphous solids prepared by melt quenching and melt quenching followed by cryogrinding showed a significant dissolution rate advantage over the γ form of indomethacin. In contrast, indomethacin that was cryoground amorphous for 1 or 3 h did not show any dissolution rate advantage over the crystalline material. Transformation was confirmed by in situ Raman microscopy and polarized light microscopy with differences seen in the nature of the crystals apparent on the surface of the dissolving solid. A portion of the melt quenched amorphous sample was annealed at 25 °C and 0% relative humidity to induce partial crystallization of γ indomethacin. As crystallinity increased, the dissolution rate decreased. The transformation time of partially amorphous indomethacin was not dependent on the level of crystallinity present, indicating only a small fraction of crystalline material needs to be present to affect the kinetics of crystallization. The solution mediated phase transformation of amorphous indomethacin is affected by the processing method even though all solids were confirmed amorphous by polarized light microscopy and X-ray diffraction. Dissolution may distinguish differences in amorphous solids that other methods cannot discern.

Received 3 July 2010; published 14 September 2010So far, the growth of spatially ordered nanoclusters by multilayer deposition has been reported and explainedsatisfactorily only in crystalline materials. Here we demonstrate a method for the growth of spatially orderednanoclusters in amorphous matrices, where the ordering is achieved in the single large domain. The regularordering is induced by the deposition of a multilayer on a periodically rippled substrate at an elevated substratetemperature. During the deposition, the nanoclusters self-arrange, following the morphology of the substrate.DOI: 10.1103/PhysRevB.82.125316 PACS number s : 68.35.bg, 61.05.cf, 68.55. a

Corrosion and heterogeneous catalysis are related through fundamental chemical processes which occur at the solid-fluid interface. Amorphous materials hold a special place in catalysis. In addition to unique catalytic activity, catalyst compositions can be chosen with diminished concern for thermodynamic constraints. These compositions represent precursors to catalytically active non-equilibrium intermediate structures. Amorphous metals which have been examined for catalysis show higher activity and selectivity than crystalline materials. This phenomenon is still not understood, but current models suggest special surface structures or known structures in higher concentrations. Knowledge of the electronic and geometric structures of catalytically active surface sites on amorphous materials is required. This paper examines known systems in terms of their unique geometric and electronic structures, and their analogs in amorphous metals are be identified. The possibility of using amorphous metals to model supported metallic systems is also addressed.

Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials that show a metal-insulator transition without a structural change are therefore of interest. Mechanisms leading to metal-insulator transition include electron correlation (Mott transition) or disorder (Anderson localization), but a clear distinction is difficult. Here we report on a metal-insulator transition on increasing annealing temperature for a group of crystalline phase-change materials, where the metal-insulator transition is due to strong disorder usually associated only with amorphous solids. With pronounced disorder but weak electron correlation, these phase-change materials form an unparalleled quantum state of matter. Their universal electronic behaviour seems to be at the origin of the remarkable reproducibility of the resistance switching that is crucial to their applications in non-volatile-memory devices. Controlling the degree of disorder in crystalline phase-change materials might enable multilevel resistance states in upcoming storage devices.