Principles Of Crystallography Research Articles

Design optimization of fuzzy controllers in building structures using the crystal structure algorithm (CryStAl)

The current study uses a recently-developed metaheuristic method called Crystal Structure Algorithm (CryStAl) to achieve optimized vibration control in structural engineering. More specifically, this algorithm, which is inspired by the well-established crystallographic principles underlying the formation of crystalline solids in nature, is applied to the optimization of fuzzy logic controllers in building structures. To demonstrate the capability of this method in solving real engineering problems, two real-size building structures, one with three and the other with twenty stories, are considered. The fuzzy controllers are implemented through an active control system to control the seismically-induced vibrations of the structures intelligently. The evaluation criteria utilized to assess the overall performance of the optimization method applied to the fuzzy control system are presented and discussed. Through nonlinear structural analyses, the ductility, energy dissipation, and other nonlinear characteristics of the structures are also considered as the structural responses to be controlled. The computational results obtained from this novel metaheuristic algorithm are compared with those of the other expert systems from the optimization literature. The findings of this paper demonstrate that the Crystal Structure Algorithm is capable of outranking the other methods in the majority of considered cases.

Phase transition and electronic properties of barium fluoride at high pressure

Pressure is a useful tool to profoundly modify the volume and electronic structure of materials, resulting in the formation of new structures with exotic physical and chemical properties. The high-symmetry cubic barium fluoride (BaF2) with a space group of Fm-3m (Z = 4) is the prototypical fluorite-type compounds at ambient condition, which is shared with many alkaline-earth fluorides. The study of high-pressure evolution of the BaF2 phase is of fundamental importance in helping to understand the structural sequence and principles of crystallography. In this work, we here have systematically investigated the high-pressure structural transition of BaF2 up to 200 GPa using an effective CALYPSO methodology. Strikingly, two thermodynamically favored phases with orthorhombic Pnma and hexagonal P63/mmc symmetry are found at 3.6 and 19.2 GPa, respectively. Distinguishingly, P63/mmc phase remains stable up to 90.5 GPa, and then transform to Pnma structure. Further electronic calculations indicate that BaF2 maintains insulating feature until 200 GPa. Our current results have broad implications for other AB2-type compounds that may harbor similar novel structured evolution behavior at high pressure.

Influence of Electron Beam Treatment of Co–Cr Alloy on the Growing Mechanism, Surface Topography, and Mechanical Properties of Deposited TiN/TiO2 Coatings

This study examines the effect of electron beam treatment (EBT) of Co–Cr substrate on the film growth mechanism, mechanical properties, and surface topography of TiN/TiO2 coatings deposited by reactive magnetron sputtering. The obtained results and processes that occurred during the deposition are discussed in the context of crystallographic principles, and special attention is paid to the crystallographic orientation and growth mechanism studied by X-ray diffraction (XRD). The mechanical properties were investigated by means of nanoindentation and wear tests. The surface topography was evaluated using atomic force microscopy (AFM). The results obtained in the present study showed that polycrystalline TiN and anatase TiO2 phases were present in all cases. Electron beam treatment of Co–Cr substrate tended to form a reorientation of the microvolumes from (111) to (200) of TiN, leading to a change in the growth mechanism from three-dimensional (Volmer–Weber) to layer-by-layer (Frank–van der Merwe). It was found that the electron beam treatment process did not significantly affect the thickness of the coatings and the deposition rate. The treatment process led to an increase in surface roughness. The higher surface roughness after the EBT process should be appropriate to support cell growth and adhesion on the surface of the deposited bilayer coating. It was demonstrated that EBT of the substrate caused a decrease in hardness of the deposited coatings from 10 to 5 GPa. The observed decrease in hardness was attributed to the change in the preferred crystallographic orientation and film growth mechanism. The hardness of the bilayer coating after the application of EBT of the Co–Cr substrate was much closer to that of human bones, which means that severe stress shielding effect could not be expected. The evaluated coefficient of friction (COF) exhibited significantly lower values in the case of EBT of the substrate compared to the untreated Co–Cr material.

AFLOW-SYM: platform for the complete, automatic and self-consistent symmetry analysis of crystals.

Determination of the symmetry profile of structures is a persistent challenge in materials science. Results often vary amongst standard packages, hindering autonomous materials development by requiring continuous user attention and educated guesses. This article presents a robust procedure for evaluating the complete suite of symmetry properties, featuring various representations for the point, factor and space groups, site symmetries and Wyckoff positions. The protocol determines a system-specific mapping tolerance that yields symmetry operations entirely commensurate with fundamental crystallographic principles. The self-consistent tolerance characterizes the effective spatial resolution of the reported atomic positions. The approach is compared with the most used programs and is successfully validated against the space-group information provided for over 54 000 entries in the Inorganic Crystal Structure Database (ICSD). Subsequently, a complete symmetry analysis is applied to all 1.7+ million entries of the AFLOW data repository. The AFLOW-SYM package has been implemented in, and made available for, public use through the automated ab initio framework AFLOW.

Enhanced oxygen storage capacity of CeO2 with doping-induced unstable crystal structure

Doping CeO2 with certain metallic ions has been shown to be an effective route to improving its oxygen storage capacity (OSC). We aimed to study the effects of dopants on the OSC of CeO2 from the perspective of crystallography. In the present study, we improved the OSC by construction of an extremely unstable CeO2 crystal structure based on crystallographic principles. By doping CeO2 with smaller Hf4+ and Sn4+ cations, the incorporated cations produced a lower cation to anion radius ratio in the crystal. The relative oxygen vacancy concentrations were 0.452 and 0.514, respectively, for 3 mol.% doping of Hf4+ and Sn4+, respectively. Our results showed that smaller dopant cations (radius of Sn4+ < Hf4+) led to more vacancies. The low temperature OSC of a CeO2 sample doped with a saturated amount of Hf4+ was 2.2 times as high as that of undoped CeO2 with a similar BET specific surface area. The partial least squares method was used to construct two linear functions for the Hf4+- and Sn4+-doping concentration vs. lattice parameters, and the relative oxygen vacancy concentration vs. low temperature OSC per BET surface area. Structure-performance relationships were developed to enable the design of CeO2 three-way catalysts.

Converse piezoelectricity and ferroelectricity in crystals of lysozyme protein revealed by piezoresponse force microscopy

ABSTRACTThis work investigates the converse piezoelectric effect in crystals of the protein lysozyme using Piezoresponse Force Microscopy (PFM) in contact and Hybrid modes. The mechanical properties of lysozyme crystals were mapped at the surface by means of Hybrid mode. In addition, ferroelectric loops were measured by the switching-spectroscopy PFM method (SS-PFM). We explore these findings using crystallographic principles and propose that the presence of defects within the crystal may lower the symmetry of lysozyme to a polar one. Our findings point towards the potential of exploiting lysozyme and other proteins in technical applications, especially those in which biocompatibility is critical.

Analysis of a NiTi Shape Memory Alloy

This work demonstrates particularly the basic properties of shape memory alloys and gives a brief review about their basic crystallographic processes. The attributes of shape memory alloys will be presented through the NiTi alloys. The crystallographic principles of three unique properties were investigated and the functional mechanism described. One of the three essential mechanisms, the one-way effect was demonstrated through an experiment. The change of length depending temperature was tested and documented. The hysteresis behavior of shape memory alloys was recorded.

Functional twin boundaries and tweed microstructures: a comparison between minerals and device materials

AbstractIn ferroelastic materials, the existence of degenerate strain states leads to the formation of nanoscale microstructures, such as domain boundaries (twin walls) and tweed. As the symmetry properties of microstructures differ from those of the bulk, they may dramatically change the macroscopic properties of a crystal. In addition, they are likely to have functional properties (ferroelecricity, piezoelectricity, magnetism, conductivity and rapid chemical transport) that are absent in the bulk. The existence of functional properties of twin walls, along with the advances in nano-scale characterization, has opened the door to domain boundary engineering, which aims to use domain boundaries as active elements in device materials. Hence, this relatively new field puts ferroelastic twin walls and possibly tweed at the heart of future electronic devices. Ferroelasticity is very common among minerals. Similar to manmade materials, the same crystallographic principles apply, which means that there are many minerals that await discovery for their functional properties. Thus, this review aims to raise attention to the discovery of minerals with functional microstructures. The current development of functional twin boundaries and tweed structures in physics and materials sciences is compared with the traditional observation of such structures in minerals. With an emphasis on chemical transport and piezoelectric/ ferroelectric behaviour, examples of functional microstructures are given from both man-made materials and minerals in addition to a discussion of the origin of polar twin walls and the introduction of a recent experimental technique, resonant piezoelectric spectroscopy (RPS), for their discovery.

High-pressure phase transition of cesium chloride and cesium bromide.

The high-symmetry cubic cesium chloride (CsCl) structure with a space group of Pm3¯m (Z = 1) is one of the prototypical AB-type compounds, which is shared with cesium halides and many binary metallic alloys. The study of high-pressure evolution of the CsCl phase is of fundamental importance in helping to understand the structural sequence and principles of crystallography. Here, we have systematically investigated the high-pressure structural transition of cesium halides up to 200 GPa using an effective CALYPSO algorithm. Strikingly, we have predicted several thermodynamically favored high-pressure phases for cesium chloride and cesium bromide (CsBr). Further electronic calculations indicate that CsCl and CsBr become metallic via band-gap closure at strong compression. The current predictions have broad implications for other AB-type compounds that likely harbor similar novel high-pressure behavior.

NMR crystallography: crystallochemical formula and space group selection

NMR crystallography determination imposes to select for a given compound under analysis the compatible space group in which it crystallizes. Up to now it was thought that NMR was not suited for this task. However, by coming back to the very principles of crystallography, it is shown in this paper that if the crystallochemical formula can be determined, by NMR or any combination of NMR with chemical information or other spectroscopy, then the compatible space groups can be straightforwardly determined by using Wyckoff's spectra of space groups. A scalar product between the crystallochemical spectrum and the space group Wyckoff's spectrum is defined that establishes if a crystallochemical formula can be embedded into a space group.

Modular design of icosahedral metal clusters

The concept of crystalline “module,” that is, an unambiguously isolated, repeated quasi-molecular element, is introduced. This concept is more general than the concept of crystal lattice. The generalized modular approach allows extension of the methods and principles of crystallography to quasi-crystals, clusters, amorphous solids, and periodic biological structures. Principles of construction of aperiodic, nonequilibrium regular modular structures are formulated. Limitations on the size of icosahedral clusters are due to the presence of spherical shells with non-Euclidean tetrahedral tiling in their structure. A parametric relationship between the structures of icosahedral fullerenes and metal clusters of the Chini series was found.

Principles of crystallography using Bragg reflection from atomically localized sources

On the basis of the two-beam model for describing element-specific Kikuchi-band effects in X-ray photoelectron diffraction (XPED), we have set up a scheme of Kikuchi-band analysis for determining structure factors and applied the method to the XPED for Ca2 p emission from a CaF 2 (111) substrate. The three-dimensional potential distribution corresponding to the fluorite structure of the CaF 2 crystal was reconstructed from the experimentally evaluated structure factors. To discuss the possibility of applying this method to epitaxial film crystallography, we have performed multiple-scattering cluster calculations for clusters of variable size and investigated the critical thickness at which Kikuchi-band effects occur.

Atomic Structure, Composition, Mechanisms and Dynamics of Transformation Interfaces in Diffusional Phase Transformations

This overview describes progress that has been made in understanding the atomic structure, composition, mechanisms and dynamics of transformation interfaces in diffusional transformations involving plate-shaped transformation products in the past eight years. Some of the important developments in the area of structure include recognition that diffusional phase transformations obey many of the same crystallographic principles developed for martensite, widespread application of high-resolution transmission electron microscopy (HRTEM) and atomistic modelling to understand interphase boundary structure and energetics, and determination of the atomic structure and energetics of high-index ledged interfaces. In the area of composition, recent development of thermal field-emission and energy-filtering HRTEM allows compositional profiling at precipitate interfaces with subnanometer spatial resolution. In addition, the position sensitive atom-probe (PoSAP), which can determine both the mass and position of individual atoms, makes it possible to map elemental distributions in some materials with atomic resolution. These techniques are expected to provide an abundance of data on composition at transformation interfaces approaching the atomic level in the near future. In terms of the dynamics of transformation interfaces, application of in situ hot-stage HRTEM to precipitate growth and dissolution has provided information on the atomic mechanisms and kinetics of ledge motion and interaction, the mechanisms and kinetics of kink nucleation, and mechanisms of faceting/roughening of precipitate plates at the atomic level. Also, kinetic models for ledge growth which are able to treat multiple-ledge interactions and time-dependent growth have been developed and are available for comparison with experimental data. In addition to discussion of these and other major developments, effort is made to emphasize current strengths and limitations in each area and indicate possible directions for future research.

Symmetry of microwave devices with gyrotropic media-complete solution and applications

In this paper, a general procedure for constructing all the possible solutions for symmetrical devices and components with gyrotropic medias is suggested. Using the theory of symmetry and crystallographic principles, all the color groups and corresponding matrices [S], [Z], and [Y] of the devices can be obtained. With this approach, it is possible to select those symmetrical structures and magnetic fields, which can be considered as candidates in the process of synthesis of microwave devices and components. In order to illustrate the procedure, some examples are given.

The hydrogen bond as a design element in crystal engineering. Two- and three-dimensional building blocks of crystal architecture

The specificity and the widespread occurrence of hydrogen bonds make them a special construction element in crystal engineering. A concise presentation of the chemical and crystallographic principles for controlled molecular association into structural building blocks, and their further organisation into three-dimensional crystal structures, is given and several examples are discussed.

The hydrogen bond as a design element in crystal engineering. Two- and three-dimensional building blocks of crystal architecture

The specificity and the widespread occurrence of hydrogen bonds make them a special constructuion element in crystal engineering. A concise presentation of the chemical and crystallographic principles for controlled molecular association into structural building blocks, and their further organisation into three-dimensional crystal structures, is given and several examples are discussed.

A comparison between three simple crystallographic principles of precipitate morphology

The connection between the optimum shape and orientation relationship of precipitates in a solid is examined. Three simple criteria for precipitate morphology are compared and illustrated schematically: the principle that precipitate dimensions tend to be inverse to the magnitude of the transformation strain; the postulate that precipitates are bounded by unrotated planes (eigenplanes); and the proposal that interfaces are parallel to the planes of three independent dislocation loop arrays necessary to accommodate the transformation strain completely. These principles are illustrated for different orientation relationships, and it is shown that special features are displayed by invariant-line precipitates. The implications of these criteria for experimental studies of precipitate morphologies are discussed and their predictions compared with results from a recent study of lath-shaped precipitates in Cu-Cr alloys.

Structural aspects of urea inclusion compounds and their investigation by X-ray diffraction: a general discussion

Structural aspects of several urea inclusion compounds (differing in the identity of the ‘guest’ species) have been investigated, principally by single-crystal X-ray diffraction. This paper discusses the general structural features that are common to these different systems. Since the structural periodicities of the host (urea) and guest molecules are generally incommensurate, it is convenient to consider the urea inclusion compound to be composed of distinguishable, although not independent, host and guest substructures. The host substructure, for example, is represented in terms of an incommensurately modulated ‘basic host structure’. The basic structure possesses three-dimensional periodicity, and can be treated using conventional crystallographic principles. The incommensurate modulation describes structural perturbations to the basic host structure which arise from host–guest interaction. Similarly, the guest substructure is considered in terms of a ‘basic guest structure’ which experiences an incommensurate modulation mediated by the host substructure. These fundamental structural concepts are developed and used as a basis for rationalizing the X-ray diffraction patterns of urea inclusion compounds.The average basic host structure has been determined from single-crystal X-ray diffraction data measured, at room temperature, via conventional diffractometric techniques. This structure is essentially the same in each compound studied, and contains linear, parallel, non-intersecting channels (tunnels) within which the guest molecules are located. The crystallographic characteristics of the basic guest structure, on the other hand, depend critically upon the identity of the guest. Full structural details of the guest substructures in the different urea inclusion compounds will be given in future publications.

On the use of distorted fcc structures for describing high-pressure phases

The paper describes distorted lattices that can be derived from the face-centred cubic Bravais lattice. Crystallographic principles are outlined and it is discussed how various lattices can be identified from the observed splitting of X-ray powder diffraction lines. Examples are taken from recent high-pressure studies of actinide rocksalt structure compounds and cerium metal.

Crystallographic principles of artificial epitaxy and its interrelation with classical epitaxy

Crystallographic principles of artificial epitaxy and its interrelation with classical epitaxy