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Showing papers on "Crystal published in 2012"


Journal ArticleDOI
TL;DR: A rational approach of the construction of a readily accessible molecular precursor, which forms a permanent porous crystal with a very high specific surface area of 3020 m g is described.
Abstract: Apart from well-established porous materials, such as zeolites, metal–organic frameworks (MOFs), covalent organic frameworks (COFs), or amorphous polymeric organic materials, porous compounds consisting exclusively of discrete organic molecules can be classified as a relatively new type of material. Such materials can be subdivided mainly into two kinds: intrinsic and extrinsic porous materials. Intrinsic porosity is defined as porosity that is already inherent in the molecular structure, such as shape-persistent voids, clefts, or cavities. Typical compounds that form intrinsic pores in the solid state are calixarenes, cucurbiturils, or shape-persistent organic cage compounds. It was shown that shapepersistent cage compounds seem to be superior within this subclass of materials, with Brunauer–Emmett–Teller (BET) surface areas of up to 2071 m g . In contrast to the high surface areas of the intrinsic porous organic materials, the values of extrinsic porous materials are significantly smaller. One of the first examples is tris(phenylenedioxy)cyclophasphazene (TPP), which was introduced in 1964 by Allcock and co-workers. Sozzani et al. demonstrated first that crystals of TPP can be permanently porous, and later, Hulliger et al. reporting a Langmuir surface area of 240 m g . The prediction of the assembling of molecules in the solid state is still very difficult, therefore it seems to be more promising to search for existing compounds that obviously exhibit pores in the crystalline state, but have not yet been proven to be permanently porous. McKeown and coworkers defined some useful criteria for such a search, and revealed that there are already quite a number of potential compounds, which fulfill those criteria. For 3,3’,4,4’-tetrakis(trimethylsilylethynyl)biphenyl (TTEB), they showed that this approach is successful: TTEB is permanently porous (BET surface area 278 m g ) and adsorbs 0.8 wt % H2 at 77 K and 10 bar. Re-investigations by Chen et al. demonstrated that HOF1a, a compound introduced before, is permanently porous, with a BET surface area of 359 m g 1 and selective adsorption of ethylene over ethane. Other extrinsic porous materials from discrete organic molecules with relatively high surface areas are SOF-1a, (BET surface area: 474 m g ), the triptycene-derived trinuclear nickel salphens of the MacLachlan group, with BET surface areas of up to 499 m g , or the macrocyclic bis(urea) CBDU (BET surface area 341 m g ). The highest BET surface area of an extrinsic organic compound were reported for PUNCs (phthalocyanine unsolvated nanoporous crystals), with values between 850 and 1002 m g . Herein, we describe a rational approach of the construction of a readily accessible molecular precursor, which forms a permanent porous crystal with a very high specific surface area of 3020 m g . For the design of the molecular structure, we have taken into account McKeown s criteria and have also systematically searched the Cambridge Structural Database for compounds that form flat ordered sheets by selfassembling by hydrogen bonding. Interestingly, almost all 4,5disubstituted benzimidazolones 22] compounds formed nearly planar ribbon-like structures by directed H-bonds of the imidazolone units (Scheme 1). Therefore, we found benzimidazolones 22] to be a potential subunit for designing our molecular precursor, exploiting the chance to form

384 citations


Journal ArticleDOI
TL;DR: Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and{001} planes, and octahedral structures with exposed {111})planes is synthesized using a very simple one-step hydrothermal method.
Abstract: Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

370 citations


Journal ArticleDOI
TL;DR: In this article, a facile and new route of synthesizing a quasi-cubic-like WO3 crystal with a nearly equal percentage of {002, {200} and {020} facets was reported, which is able to photoreduce CO2 to generate CH4 in the presence of H2O vapor.
Abstract: The reactivity of a photocatalyst is basically influenced by its surface atomic and linked electronic structure. Tuning different crystal facets is becoming an important strategy to optimize the reactivity of a photocatalyst for targeted reactions. Here we report a facile and new route of synthesizing a quasi-cubic-like WO3 crystal with a nearly equal percentage of {002}, {200} and {020} facets, and a rectangular sheet-like WO3 crystal with predominant {002} facet by controlling acidic hydrolysis of crystalline WB. As a result of electronic structure effects induced by crystal facet, the quasi-cubic-like WO3 crystal with a deeper valence band maximum shows a much higher O2 evolution rate in photocatalytic water oxidation than the rectangular sheet-like WO3 crystal. The latter, with an elevated conduction band minimum of 0.3 eV, is able to photoreduce CO2 to generate CH4 in the presence of H2O vapor.

341 citations


Journal ArticleDOI
TL;DR: This work found a large decrease of the kink-pair formation enthalpy due to the quantization of the crystal vibrational modes, which means that the flow stress predicted by Orowan's law is strongly reduced when compared with its classical approximation and in much closer agreement with experiments.
Abstract: Crystal plasticity involves the motion of dislocations under stress. So far, atomistic simulations of this process have predicted Peierls stresses, the stress needed to overcome the crystal resistance in the absence of thermal fluctuations, of more than twice the experimental values, a discrepancy best-known in body-centred cubic crystals. Here we show that a large contribution arises from the crystal zero-point vibrations, which ease dislocation motion below typically half the Debye temperature. Using Wigner's quantum transition state theory in atomistic models of crystals, we found a large decrease of the kink-pair formation enthalpy due to the quantization of the crystal vibrational modes. Consequently, the flow stress predicted by Orowan's law is strongly reduced when compared with its classical approximation and in much closer agreement with experiments. This work advocates that quantum mechanics should be accounted for in simulations of materials and not only at very low temperatures or in light-atom systems.

198 citations


Journal ArticleDOI
TL;DR: In this paper, aggregated CaWO4 micro- and nanocrystals were synthesized by the co-precipitation method and processed under microwave-assisted hydrothermal/solvothermal conditions (160 °C for 30 min).
Abstract: In this paper, aggregated CaWO4 micro- and nanocrystals were synthesized by the co-precipitation method and processed under microwave-assisted hydrothermal/solvothermal conditions (160 °C for 30 min). According to the X-ray patterns, all crystals exhibited only the scheelite-type tetragonal structure. The data obtained by the Rietveld refinements revealed that the oxygen atoms occupy different positions in the [WO4] clusters, suggesting the presence of lattice distortions. The crystal shapes as well as its crystallographic orientations were identified by field-emission scanning electron microscopy and high-resolution transmission electron microcopy. Electronic structures of these crystals were evaluated by the first-principles quantum mechanical calculations based on the density functional theory in the B3LYP level. A good correlation was found between the experimental and theoretical Raman and infrared-active modes. A crystal growth mechanism was proposed to explain the morphological evolution. The ultraviolet-visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The highest blue photoluminescence emission, lifetime and quantum yield were observed for the nanocrystals processed in the microwave-assisted solvothermal method.

197 citations


Journal ArticleDOI
01 Jan 2012-Carbon
TL;DR: In this paper, the effect of parent graphite on the structure of graphene oxide (GO) was investigated using high purity graphites with a uniform crystallite size, and the results provided direct evidence of how the size of the graphite crystal affects the oxidation process and the functionality and sheet size of resulting GO.

194 citations


Journal ArticleDOI
TL;DR: Construction of heterostructures with p -type and n -type semiconductors constitutes an effi cient way to realize ambipolar operation.
Abstract: and two-component transistors with the combination of p -type and n -type semiconductors. [ 4–6 ] Ambipolar transport materials are particularly desirable concerning the construction of complementary-like circuits, as the fabrication processes could be signifi cantly simplifi ed when two unipolar materials were replaced with an ambipolar material. Despite the huge progresses in organic semiconductors, the ambipolar transport materials are still rare with respect to unipolar materials, and it is still a great challenge in design and synthesis of π -conjugated systems that could fulfi ll the requirement for achieving both stable p -type and n -type transport in ambient condition. As an alternative choice, construction of heterostructures with p -type and n -type semiconductors constitutes an effi cient way to realize ambipolar operation. For example, bilayer heterojunction, [ 4 ] bulk heterojunction [ 5 ] and lateral heterostructure [ 6 ] have been successfully demonstrated to fabricate

192 citations


Journal ArticleDOI
TL;DR: A computational approach is presented for the design of proteins that self-assemble in three dimensions to yield macroscopic crystals and has potential applications to the de novo design of nanostructured materials and to the modification of natural proteins to facilitate X-ray crystallographic analysis.
Abstract: Protein crystals have catalytic and materials applications and are central to efforts in structural biology and therapeutic development. Designing predetermined crystal structures can be subtle given the complexity of proteins and the noncovalent interactions that govern crystallization. De novo protein design provides an approach to engineer highly complex nanoscale molecular structures, and often the positions of atoms can be programmed with sub-Å precision. Herein, a computational approach is presented for the design of proteins that self-assemble in three dimensions to yield macroscopic crystals. A three-helix coiled-coil protein is designed de novo to form a polar, layered, three-dimensional crystal having the P6 space group, which has a “honeycomb-like” structure and hexameric channels that span the crystal. The approach involves: (i) creating an ensemble of crystalline structures consistent with the targeted symmetry; (ii) characterizing this ensemble to identify “designable” structures from minima in the sequence-structure energy landscape and designing sequences for these structures; (iii) experimentally characterizing candidate proteins. A 2.1 Å resolution X-ray crystal structure of one such designed protein exhibits sub-Å agreement [backbone root mean square deviation (rmsd)] with the computational model of the crystal. This approach to crystal design has potential applications to the de novo design of nanostructured materials and to the modification of natural proteins to facilitate X-ray crystallographic analysis.

166 citations


Journal ArticleDOI
TL;DR: In this article, a facile one-step growth of self-aligning, highly crystalline soluble acene arrays that exhibit excellent field-effect mobilities was reported via an optimized dip-coating process.
Abstract: The preparation of uniform large-area highly crystalline organic semiconductor thin films that show outstanding carrier mobilities remains a challenge in the field of organic electronics, including organic field-effect transistors. Quantitative control over the drying speed during dip-coating permits optimization of the organic semiconductor film formation, although the kinetics of crystallization at the air–solution–substrate contact line are still not well understood. Here, we report the facile one-step growth of self-aligning, highly crystalline soluble acene crystal arrays that exhibit excellent field-effect mobilities (up to 1.5 cm V−1 s−1) via an optimized dip-coating process. We discover that optimized acene crystals grew at a particular substrate lifting-rate in the presence of low boiling point solvents, such as dichloromethane (b.p. of 40.0 °C) or chloroform (b.p. of 60.4 °C). Variable-temperature dip-coating experiments using various solvents and lift rates are performed to elucidate the crystallization behavior. This bottom-up study of soluble acene crystal growth during dip-coating provides conditions under which one may obtain uniform organic semiconductor crystal arrays with high crystallinity and mobilities over large substrate areas, regardless of the substrate geometry (wafer substrates or cylinder-shaped substrates).

165 citations


Journal ArticleDOI
TL;DR: The proposed space-time crystals of trapped ions provide a new dimension for exploring many-body physics and emerging properties of matter and are robust for direct experimental observation.
Abstract: Spontaneous symmetry breaking can lead to the formation of time crystals, as well as spatial crystals. Here we propose a space-time crystal of trapped ions and a method to realize it experimentally by confining ions in a ring-shaped trapping potential with a static magnetic field. The ions spontaneously form a spatial ring crystal due to Coulomb repulsion. This ion crystal can rotate persistently at the lowest quantum energy state in magnetic fields with fractional fluxes. The persistent rotation of trapped ions produces the temporal order, leading to the formation of a space-time crystal. We show that these space-time crystals are robust for direct experimental observation. We also study the effects of finite temperatures on the persistent rotation. The proposed space-time crystals of trapped ions provide a new dimension for exploring many-body physics and emerging properties of matter.

164 citations


Journal ArticleDOI
TL;DR: The design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry equipped with a segmented-type crystal for x-ray diffraction and an energy resolution in the order of 0.25 eV and 1 eV is reported.
Abstract: We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV-9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.

Journal ArticleDOI
TL;DR: In this paper, a new dicyanodistyryrylbenzene-based phasmidic molecule, (2Z,2′Z)-2, 2′-(1,4-phenylene)bis(3-(3,4,5-tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT).
Abstract: A new dicyanodistyrylbenzene-based phasmidic molecule, (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(3,4,5-tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT). GDCS molecules self-assemble into supramolecular disks consisting of a pair of molecules in a side-by-side disposition assisted by secondary bonding interactions of the lateral polar cyano group, which, in turn, constitute the hexagonal columnar LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystalline states, respectively, in contrast to the total absence of fluorescence emission in the isotropic melt state according to the characteristic aggregation-induced enhanced emission (AIEE) behavior. The AIEE and two-color luminescence thermochromism of GDCS are attributed to the peculiar intra- and intermolecular interactions of dipolar cyanostilbene units. It was found that the intramolecular planarization and restricted molecular motion associated with a specific stacking situation in the liquid/solid crystalline phases are responsible for the AIEE phenomenon. The origin of the two-color luminescence was elucidated to be due to the interdisk stacking alteration in a given column driven by the specific local dipole coupling between molecular disks. These stacking changes, in turn, resulted in the different degree of excited-state dimeric coupling to give different emission colors. To understand the complicated photophysical properties of GDCS, temperature-dependent steady-state and time-resolved PL measurements have been comprehensively carried out. Uniaxially aligned and highly fluorescent LC and crystalline microwires of GDCS are fabricated by using the micromolding in capillaries (MIMIC) method. Significantly enhanced electrical conductivity (0.8 × 10−5 S•cm−1/3.9 × 10−5 S•cm−1) of the aligned LC/crystal microwires were obtained over that of multi-domain LC sample, because of the almost perfect shear alignment of the LC material achieved in the MIMIC mold.

Journal ArticleDOI
TL;DR: In this article, a review of the nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications is presented. But the main focus of this review is on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems.
Abstract: Rare earth (RE) doped oxyfluoride glass ceramics possess interesting optical properties with applications in telecommunications and optoelectronics, such as solid state lasers, optical amplifiers, etc. These materials combine the transparency and mechanical and chemical resistance of aluminosilicate glasses with the low phonon energy and facile incorporation of RE ions in the fluoride crystals. The incorporation of RE ions in the crystalline phases enhances the laser emission intensity, a major property of these materials. Transparency is achieved when crystal size is in the nanometric scale, usually below 40 nm, which avoids light scattering. A strict control of the nucleation and crystal growth processes is therefore necessary which requires a deep knowledge of the crystallisation mechanisms. The great activity and publications in this field in the last decades merit a review providing a comparative study of the different nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications. This is the objective of this review paper which includes 227 references. A general discussion on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems. In the second section, the principal RE doped glass ceramics are presented. After a general introduction about the luminescence processes, including up- and down-conversion, the behaviour of RE elements in glasses and crystals are discussed. Glass ceramic compositions have been divided as follows: glass ceramics with a glass composition following Wang and Ohwaki’s oxyfluoride glass ceramic, and glass ceramics with different matrix compositions, arranged by crystalline phases. Relevant properties, mainly optical and laser, are described in each system along with the most relevant applications of these materials.

Journal ArticleDOI
TL;DR: In this article, Monte Carlo simulations and free-energy calculations are used to determine the phase diagram of colloidal hard superballs, of which the shape interpolates between cubes and octahedra via spheres.
Abstract: For hard anisotropic particles the formation of a wide variety of fascinating crystal and liquid-crystal phases is accomplished by entropy alone. A better understanding of these entropy-driven phase transitions will shed light on the self-assembly of nanoparticles, however, there are still many open questions in this regard. In this work, we use Monte Carlo simulations and free-energy calculations to determine the phase diagram of colloidal hard superballs, of which the shape interpolates between cubes and octahedra via spheres. We discover not only a stable face-centered cubic (fcc) plastic crystal phase for near-spherical particles, but also a stable body-centered cubic (bcc) plastic crystal close to the octahedron shape. Moreover, coexistence of these two plastic crystals is observed with a substantial density gap. The plastic fcc and bcc crystals are, however, both unstable in the cube and octahedron limit, suggesting that the local curvature, i.e. rounded corners and curved faces, of superballs plays an important role in stabilizing the rotator phases. In addition, we observe a two-step melting phenomenon for hard octahedra, in which the Minkowski crystal melts into a metastable bcc plastic crystal before melting into the fluid phase.

Journal ArticleDOI
TL;DR: In this article, the crystal orientation of β -Ga 2 O 3 thin films was studied in detail using X-ray diffraction, pole figure measurements and analysis using a crystal model.

Journal ArticleDOI
TL;DR: Recent studies of the polymorphic and thermotropic properties of crystalline materials embedded in the nanometer-scale pores of porous glass powders and porous block-polymer-derived plastic monoliths are reviewed, suggesting a reliable approach to studying the phase behaviors of compounds at the nanoscale.
Abstract: The phase behaviors of crystalline solids embedded within nanoporous matrices have been studied for decades. Classic nucleation theory conjectures that phase stability is determined by the balance between an unfavorable surface free energy and a stabilizing volume free energy. The size constraint imposed by nanometer-scale pores during crystallization results in large ratios of surface area to volume, which are reflected in crystal properties. For example, melting points and enthalpies of fusion of nanoscale crystals can differ drastically from their bulk scale counterparts. Moreover, confinement within nanoscale pores can dramatically influence crystallization pathways and crystal polymorphism, particularly when the pore dimensions are comparable to the critical size of an emerging nucleus. At this tipping point, the surface and volume free energies are in delicate balance and polymorph stability rankings may differ from bulk. Recent investigations have demonstrated that confined crystallization can be u...

Journal ArticleDOI
TL;DR: In this paper, hyperbranched Zn2GeO4 nanoarchitectures were successfully synthesized in a binary ethylenediamine (En)/water solvent system using a solvothermal route.
Abstract: Sheaf-like, hyperbranched Zn2GeO4 nanoarchitectures were successfully synthesized in a binary ethylenediamine (En)/water solvent system using a solvothermal route. These structures may be assigned to the splitting crystal growth mechanism, resembling some minerals observed in nature. Addition of increasing amounts of En was found to enhance the degree of crystal splitting. Nitridation of the resulting Zn2GeO4 superstructures under NH3 flow produced yellow Zn1.7GeN1.8O solid solution, which allows photocatalytically converse CO2 into hydrocarbon fuel (CH4) in the presence of H2O at ambient conditions under visible light irradiation.

Journal ArticleDOI
TL;DR: In this article, the authors showed that perovskite (Ba,La)SnO3 can have excellent carrier mobility even though its band gap is large, and the Hall mobility of Ba0.98La 0.02snO3 crystals with the n-type carrier concentration of \sim 8-10\times10 19 cm-3 is found to be \sim 103 cm2 V-1s-1 at room temperature.
Abstract: We discovered that perovskite (Ba,La)SnO3 can have excellent carrier mobility even though its band gap is large. The Hall mobility of Ba0.98La0.02SnO3 crystals with the n-type carrier concentration of \sim 8-10\times10 19 cm-3 is found to be \sim 103 cm2 V-1s-1 at room temperature, and the precise measurement of the band gap \Delta of a BaSnO3 crystal shows \Delta=4.05 eV, which is significantly larger than those of other transparent conductive oxides. The high mobility with a wide band gap indicates that (Ba,La)SnO3 is a promising candidate for transparent conductor applications and also epitaxial all-perovskite multilayer devices.


Journal ArticleDOI
TL;DR: In this paper, a growth model for binary symmetrical electrolyte crystals was proposed to account for the dependence of calcite crystal growth rate on the cation to anion ratio in solution.

Journal ArticleDOI
Xiaochuan Duan1, Jiaqin Yang1, Haiyan Gao1, Jianmin Ma1, Lifang Jiao1, Wenjun Zheng1 
TL;DR: In this article, four well-defined morphologies, including nanorod, nanowire, nanoflower and nanowall, of MnO2 nanostructures with different crystal phases (α-, β-, and δ-MnO2) have been synthesized employing a simple hydrothermal process.
Abstract: In this work, four well-defined morphologies, including nanorod, nanowire, nanoflower and nanowall, of MnO2 nanostructures with different crystal phases (α-, β-, and δ-MnO2) have been synthesized employing a simple hydrothermal process. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) spectrometry. Our experimental results demonstrate that the concentration of KMnO4 plays a key role in forming different shapes and phases of MnO2 nanostructures. Specifically, the K+ concentration can affect the crystal phase of MnO2 seeds in the nucleation processes and the decomposition rate of MnO4− can influence the number of MnO2 nuclei at the initial nucleating stage and also can affect the subsequent crystal growth process. Moreover, the effects of reaction temperature on the morphology of the δ-MnO2 nanowall are systematically studied. The electrochemical performances of the as-prepared MnO2 as the positive material of rechargeable Li-ion batteries have also been researched. It is found that the δ-MnO2 nanowall possesses largely enhanced electrochemical activity compared to α-MnO2 nanowires and β-MnO2 nanorods. The vast difference in electrochemical activity is discussed in terms of the morphology, crystal phase and specific surface area of MnO2 nanostructures. It is highly expected that these findings are useful in understanding the formation of MnO2 nanocrystals with different morphologies, which are also applicable to other metal oxides nanocrystals.

Journal ArticleDOI
TL;DR: In this article, the deformation induced crystal-crystal transition of polybutene-1 (PB-1) from forms II to I at different temperatures was studied with in situ synchrotron radiation wide-angle X-ray scattering (WAXS).
Abstract: Deformation induced crystal–crystal transition of polybutene-1 (PB-1) from forms II to I at different temperatures is studied with in situ synchrotron radiation wide-angle X-ray scattering (WAXS). Analyses on the evolution of crystallinity and orientations of forms II and I during tensile deformation show that stretch accelerates the transformation from forms II to I, which is interpreted based on either a direct crystal–crystal transition or an indirect approach via an intermediate state of melt, namely a melting recrystallization process. A three-stage mechanical deformation including linear deformation, stress plateau, and strain hardening is observed in the engineering stress–strain curves, which corresponds to a process of incubation, nucleation, and gelation of form I crystals. It establishes a nice correlation between phase transition and mechanical behavior in this study.

Book
13 Aug 2012
TL;DR: In this paper, the authors present a theoretical analysis of the thermodynamic properties of binary alloys in terms of their properties, properties of interfaces, and their properties of interfaces.
Abstract: Preface Chapter 1 Thermodynamic Concepts and Relationships 1.1 Introduction 1.2 Thermodynamic Concepts and Relationships 1.3 Thermodynamics of Single Component Systems 1.4. Thermodynamics of Multiple Component Systems 1.5 Thermodynamics of Alloys 1.6 Thermodynamics of Ideal Binary Solutions 1.7 Thermodynamics of Non-Ideal Binary Solutions 1.8 Experimental Determination of Thermodynamic Quantities of Binary Alloys Summary Chapter 2 Thermodynamics Analysis of Solidification Processes in Metals and Alloys 2.1 Introduction 2.2 Thermodynamics of Pure Metals 2.3 Thermodynamics of Binary Alloys 2.4 Equilibrium between Phases in Binary Solutions. Phase Diagrams of Binary Alloys 2.5 Driving Force of Solidification in Binary Alloys 2.6 Thermodynamics of Ternary Alloys 2.7 Thermodynamics of Vacancies in Pure Metals and Alloys Summary Exercises References Chapter 3 Properties of Interfaces 3.1 Introduction 3.2 Classical Theory of Interface Energy and Surface Tension 3.3 Thermodynamics of Interfaces 3.4 Structures of Interfaces 3.5 Equilibrium Shapes of Crystals Summary Exercises References Chapter 4 Nucleation 4.1 Introduction 4.2 Homogeneous Nucleation 4.3 Heterogeneous Nucleation. Inoculation 4.4 Nucleation of Bubbles 4.5 Crystal Multiplication Summary Exercises References Chapter 5 Crystal Growth in Vapours 5.1 Introduction 5.2 Crystal Morphologies 5.3 Chemical Vapour Deposition 5.4 Crystal Growth 5.5 Normal Crystal Growth of Rough Surfaces in Vapours 5.6 Layer Crystal Growth of Smooth Surfaces in Vapours 5.7 Influence of Impurities on Crystal Growth in Vapours 5.8 Epitaxial Growth 5.9 Whisker Growth 5.10 Mechanical Restrictions on Thin Films Summary Exercises References Chapter 6 Crystal Growth in Liquids and Melts 6.1 Introduction 6.2 Structures of Crystals and Melts 6.3 Growth Methods 6.4 Crystal Growth 6.5 Volume Changes and Relaxation Processes during Anelastic Crystal Growth in Metal Melts 6.6 Normal Crystal Growth in Pure Metal Melts 6.7 Layer Crystal Growth of Smooth Surfaces in Liquids 6.8 Normal Crystal Growth in Binary Alloys 6.9 Diffusion Controlled Growth of Planar Crystals in Binary Alloys 6.10 Diffusion Controlled Growth of Spherical Crystals in Alloys 6.11 Impingement 6.12 Precipitation of Pores Summary Exercises References Chapter 7 Heat Transport during Solidification Processes.Thermal Analysis 7.1 Introduction 7.2 Basic Concepts and Laws of Heat Transport 7.3 Convection 7.4 Theory of Heat Transport at Unidirectional Solidification 7.5 Production of Single Crystals by Unidirectional Solidification 7.6 Thermal Analysis 7.7 Variable Heat of Fusion of Metals and Alloys 7.8 Variable Heat Capacitivity of Metals and Alloys Summary Exercises References Chapter 8 Crystal Growth Controlled by Heat and Mass Transport 8.1 Introduction 8.2 Heat and Mass Transports in Alloys during Unidirectional Solidification 8.3 Zone Refining 8.4 Single Crystal Production by Czochralski Technique 8.5 Cellular Growth. Constitutional Undercooling. Interface Stability Summary Exercises References Chapter 9 Faceted and Dendritic Solidification Structures 9.1 Introduction 9.2 Formation of Faceted Crystals 9.3 Growth of Faceted Crystals in Pure Metal Melts 9.4 Growth of Faceted Crystals in Alloy Melts 9.5 Growth of Dendritic Crystals 9.6 Development of Dendrites 9.7 Transitions between Structure Types in Alloys Summary Exercises References Chapter 10 Eutectic Solidification Structures 10.1 Introduction 10.2 Classification of Eutectic Structures 10.3 Normal Eutectic Growth 10.4 Degenerate and Coupled Eutectic Growth 10.5 Structures of Ternary Alloys 10.6 Solidification of Fe-C Eutectics 10.7 Solidification of Al-Si Eutectics 10.8 Transitions between Normal Lamellar and Rod Eutectic Growths Summary Exercises References Chapter 11 Peritectic Solidification Structures 11.1 Introduction 11.2 Peritectic Reactions and Transformations 11.3 Peritectic Reactions and Transformations in Iron-Base Alloys 11.4 Metastable Reactions in Iron-Base Alloys 11.5 Metatectic Reactions and Transformations 11.6 Microsegregation in Iron-Base Alloys 11.7 Transition between Peritectic and Eutectic Reactions in in Iron-Base Alloys Summary Exercises References Chapter 12 Metallic Glasses and Amorphous Alloy Melts 12.1 Introduction 12.1 History and Development of Amorphous Alloys 12.2 Basic Concepts and Definitions 12.3 Production of Metallic Glasses 12.4 Experimental Methods for Structure Determination of Metallic Glasses and Amorphous Alloy Melts 12.5 Structure of Metallic Glasses 12.6 Comparison of the Structures of Metallic Glasses and Amorphous Alloy Melts. Rough Model of Metallic Glasses and Amorphous Alloy Melts 12.7 Casting of Metallic Glasses. Crystallization Processes in Amorphous Alloy Melts 12.8 Classification of Metallic Glasses 12.9 Properties and Applications of Metallic Glasses Summary Exercises References Answers to Exercises Index

Journal ArticleDOI
TL;DR: In this article, the crystal and electronic band structures of CuxS(1.25, 1.75, and cubic-chalcocite phases have been systematically studied using the density functional theory method.
Abstract: The crystal and electronic band structures of CuxS(1.25 < x ≤ 2) are systematically studied using the density-functional theory method. For Cu2S, all the three chalcocite phases, i.e., the low-chalcocite, the high-chalcocite, and the cubic-chalcocite phases have direct band gaps around 1.3–1.5 eV, with the low-chalcocite being the most stable one. However, Cu vacancies can form spontaneously in these compounds, causing instability of Cu2S. We find that under Cu-rich condition, the anilite Cu1.75S is the most stable structure. It has a predicted band gap of 1.4 eV and could a promising solar cell absorber.

Journal ArticleDOI
TL;DR: Cu(2)FeSnS(4) (CFTS) nanocrystals with tunable crystal phase have been synthesized using a solution-based method and appear attractive as a low-cost substitute for thin film solar cells.

Journal ArticleDOI
TL;DR: In this paper, a gradient-enhanced crystal plasticity model is presented that explicitly accounts for the evolution of the densities of geometrically necessary dislocations (GNDs) on individual slip systems of deforming crystals.
Abstract: A gradient-enhanced crystal plasticity model is presented that explicitly accounts for the evolution of the densities of geometrically necessary dislocations (GNDs) on individual slip systems of deforming crystals. The GND densities are fully coupled with the crystal slip rule. Application of the model to two distinct and technologically important crystal types, namely hcp Ti and ccp Ni, is given. For the hcp crystals, slip is permitted with a-type slip directions on basal, prismatic and pyramidal planes and c + a-type slip directions on pyramidal planes. First, a single crystal under four-point bending is simulated as the uniform strain gradient expected in the central span provides a good validation of the code. Then, uniaxial deformation of a model near-a Ti polycrystal has been analysed. The resulting distributions of GND densities that develop on the various slip system types have been compared with independent experimental observations. The model predicts that GND density on the c + a systems is approximately an order of magnitude lower than that for a-type systems in agreement with experiment. For the ccp case, slip is considered to take place on the {111} slip systems. Thermal loading of a single-crystal nickel alloy sample containing carbide particles of size approximately 30mm has been analysed. Detailed comparisons are presented between model predictions and results of high-resolution electron backscatter diffraction (EBSD) measurements of the micro-deformations, lattice rotations, curvatures and GND densities local to the nickel–carbide interface. Qualitatively, good agreement is achieved between the coupled and decoupled model elastic strains with the EBSD measurements, but lattice rotations and GND densities are quantitatively well predicted by the coupled crystal model but are less well captured by the decoupled model. The GND coupling is found to lead to reduced lattice rotations and plastic strains in the region of highest heterogeneity close to the Ni matrix/particle interface, which is in agreement with the experimental measurements. The results presented provide objective evidence of the effectiveness of gradient-enhanced crystal plasticity finite element analysis and demonstrate that GND coupling is required in order to capture strains and lattice rotations in regions of high heterogeneity.

Journal ArticleDOI
13 Jun 2012-Langmuir
TL;DR: This analysis indicates a rearrangement of structural packing within the fibers in the naphthalene dipeptides, consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth.
Abstract: Naphthalene dipeptides have been shown to be useful low-molecular-weight gelators. Here we have used a library to explore the relationship between the dipeptide sequence and the hydrogelation efficiency. A number of the naphthalene dipeptides are crystallizable from water, enabling us to investigate the comparison between the gel/fiber phase and the crystal phase. We succeeded in crystallizing one example directly from the gel phase. Using X-ray crystallography, molecular modeling, and X-ray fiber diffraction, we show that the molecular packing of this crystal structure differs from the structure of the gel/fiber phase. Although the crystal structures may provide important insights into stabilizing interactions, our analysis indicates a rearrangement of structural packing within the fibers. These observations are consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth. This observation has an impact on the use of crystal structures to determine supramolecular synthons for gelators.

Journal ArticleDOI
TL;DR: In this article, the authors employed the bond valence method to identify materials with crystal structures featuring infinite networks of pathways of suitable size that is a prerequisite for fast ion transport, and carried out exhaustive analysis of ~13,000 entries of the Inorganic Crystal Structure Database and ranked the materials based on the fraction of crystal structure space with low bond-valence mismatch.

Journal ArticleDOI
TL;DR: It is shown that accurate results can be obtained from a monomer-based many-body expansion truncated at the two-body level, with the monomer and dimer calculations suitably embedded in a model of the crystalline environment.
Abstract: Reliable prediction of molecular crystal energetics is a vital goal for computational chemistry. Here we show that accurate results can be obtained from a monomer-based many-body expansion truncated at the two-body level, with the monomer and dimer calculations suitably embedded in a model of the crystalline environment. By including the two dominant effects--electrostatics and exchange-repulsion--we are able to capture the important nonadditive terms in the energy, and approach very closely results from full periodic second-order Moller-Plesset calculations. The advantage of the current scheme is that extension to coupled-cluster and explicitly correlated F12 methods is completely straightforward. We demonstrate the approach through calculations on carbon dioxide, hydrogen fluoride, and ice XIh and XIc. In accord with previous studies, we find these two ice polymorphs to be very close in energy, with our periodic coupled-cluster single double triple-F12 calculation giving the hexagonal structure more stable by around 0.3 kJ mol(-1).

Journal ArticleDOI
TL;DR: A combined scanning electron microscope, transmission electron microscopy, and scanning tunneling microscopy study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy finds correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth.
Abstract: III‐V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs1 xSbx nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs1 xSbx heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core‐shell structure, with an Sb-rich shell.