The aim of this diploma thesis is to investigate microstructure and thermal stability of ultra fine grained magnesium alloys. The thesis first summarises methods using plastic deformation in order to achieve ultra fine grained structure that are used to process metals. Then experimental methods employed in the experimental part including microhardness testing, scanning electron microscopy and positron annihilation spectroscopy are described. Brief summary of previous research on MgZnY alloys strengthened by quasicrystalline phases and Mg22Gd alloys is given. Finally, results of experimental investigation of MgZnY alloys with various Zn/Y ratios and Mg22Gd alloy are discussed. These results suggest that presence of phases in MgZnY alloys depend on Zn/Y ratio, hardness of these alloys depends on Zn content and that rapid cooling of MgZnY alloys annealed at 500 řC lead to significant increase in volume fraction of quasicrystalline icosahedral phase. In the second section of the experimental part thermal behaviour of Mg22Gd alloy is investigated. Furthermore, formation of GdH2 particles in Mg22Gd is examined and attributed to reaction of hydrogen decomposed from water vapour with gadolinium in areas rich in gadolinium. Finally, significant hardening of Mg22Gd alloy processed by high pressure torsion has been...

This licentiate thesis presents developments of nanocalorimetry systems tailored for use under extreme conditions such as high pressure, intense magnetic fields, and low temperature. Nanocalorimetry is a powerful approach to study strongly correlated systems like superconductors, heavy fermions, and quantum materials with non-trivial magnetic or electronic properties, materials with emergent magnetic orders, as well as quasicrystals. Introducing high pressure or magnetic fields as tuning parameters in specific heat measurements at low temperatures can enhance the understanding of underlying physical properties of such materials. The key component of calorimeters is the thermometer. A thin-film thermometer based on a composite ceramic metal oxide has been developed. It shows high sensitivity and negligible magnetoresistance over a broad temperature range. Two different nanocalorimeters are fabricated starting from an existing nanocalorimeter design, a high-pressure nanocalorimeter and a calorimeter for sample rotations in high magnetic fields. The high-pressure nanocalorimetry setup involves a nanocalorimeter built on a robust substrate combined with a diamond anvil cell, a gasket sandwich with electric leads, and an optical setup for pressure detection through ruby fluorescence spectroscopy. The high-field nanocalorimeters are fabricated on SiNx membranes for specific heat measurements down to 30 mK. Miniaturization is performed to extend their use for angular-dependent measurements in high magnetic fields, so far used up to 41 T. Reducing the calorimeter platform size in both calorimeters is achieved by a method of plasma etching performed after device fabrication. Specific heat measurements of Eu-doped GdCd7.88 quasicrystals and GdCd6 approximant systems are performed in fields up to 12 T. The preliminary results show the presence of spin-glass behavior in the quasicrystals and an antiferromagnetic transition in the approximant crystals at low temperatures.

No / Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.

L'étude des phases de la matière est d'un intérêt fondamental en physique. La théorie de Landau, qui est le "modèle standard" des transitions de phases, caractérise les phases de la matière en termes des brisures de symétrie, décrites par un paramètre d'ordre local. Cette théorie a permis la description de phénomènes remarquables tels que la condensation de Bose-Einstein, la supraconductivité et la superfluidité.<p><p>Il existe cependant des phases qui échappent à la description de Landau. Il s'agit des phases quantiques topologiques. Celles-ci constituent un nouveau paradigme et sont caractérisées par un ordre global défini par un invariant topologique. Ce dernier classe les objets ou systèmes de la manière suivante: deux objets appartiennent à la même classe topologique s'il est possible de déformer continument le premier objet en le second. Cette propriété globale rend le système robuste contre des perturbations locales telles que le désordre. <p><p>Les atomes froids constituent une plateforme idéale pour simuler les phases quantiques topologiques. Depuis l'invention du laser, les progrès en physique atomique et moléculaire ont permis un contrôle de la dynamique et des états internes des atomes. La réalisation de gaz quantiques,tels que les condensats de Bose-Einstein et les gaz dégénérés de Fermi, ainsi que la réalisation de réseaux optiques à l'aide de faisceaux lasers, permettent d'étudier ces nouvelles phases de la matière et de simuler aussi la physique du solide cristallin.<p><p>Dans cette thèse, nous nous concentrons sur l'etude d'isolants topologiques avec des atomes froids. Ces derniers sont isolants de volume mais possèdent des états de surface qui sont conducteurs, protégés par un invariant topologique. Nous traitons trois sujets principaux. Le premier sujet concerne la génération dynamique d'un isolant topologique de Mott. Ici, les interactions engendrent l'isolant topologique et ce, sans champ de jauge de fond. Le second sujet concerne la détection des isolants topologiques dans les expériences d'atomes froids. Nous proposons deux méthodes complémentaires pour caractériser celles-ci. Finalement, le troisième sujet aborde des thèmes au-delà de la définition standard d'isolant topologique. Nous avons d'une part proposé un algorithme efficace pour calculer la conductivité de Berry, la contribution topologique à la conductivité transverse lorsque l'énergie de Fermi se trouve dans une bande d'énergie. D'autre part, nous avons utilisé des méthodes pour caractériser les propriétés quantiques topologiques de systèmes non-périodiques.<p><p>L'étude des isolants topologiques dans les expériences d'atomes froids est un sujet de recherche récent et en pleine expansion. Dans ce contexte, cette thèse apporte plusieurs contributions théoriques pour la simulation de systèmes quantiques sur réseau avec des atomes froids. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.

<p>Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.</p>

The main goal of the dissertation was to reveal the electronic structure of ZnMgRE (RE = Y, Ho, Er) quasicrystals by investigations of their optical response. The thesis comprises experimental X-ray diffraction (XRD) and optical spectroscopy studies of the quasicrystals, a construction of their electron subsystem model, and a theoretical description of their optical response. The XRD studies were carried out to determine the reciprocal quasicrystalline lattice vectors, which define the atomic potential field acting on an electron subsystem. The optical spectroscopy studies were carried out by the combined spectroscopic ellipsometry and reflectance spectroscopy technique, based on a suggested anchor-window method. High-accuracy ZnMgRE optical conductivity spectra were recorded in the wide, 0.01 – 6 eV, spectral range. The model of ZnMgRE electron energy spectrum, previously suggested for an interpretation of experimental ZnMgRE photoemission spectra, was developed. The nearly-free-electron gas model of independent intersections was formulated in the extended zone presentation. A scheme of the theoretical optical conductivity calculations was extended to account for various positions of the Fermi level with respect to a pseudogap. The experimental ZnMgRE optical conductivity spectra can be reproduced in detail by theoretical calculations performed within the framework of the suggested electron energy spectrum model. The set of the electron energy spectrum parameters determined... [to full text] / Pagrindinis disertacijos tikslas – optinio ZnMgRE (RE = Y, Ho, Er) kvazikristalų atsako tyrimais atskleisti jų elektroninės posistemės ypatumus. Disertaciją sudaro eksperimentiniai rentgeno-difrakciniai (XRD) ir optiniai spektroskopiniai tyrimai, kvazikristalų elektroninės posistemės modelio konstravimas ir teorinis jų optinio atsako aprašymas. Atliktais eksperimentiniais XRD tyrimais buvo siekiama atskleisti kvazikristalų atvirkštinės gardelės vektorius, apibrėžiančius potencinį kvazikristalinį lauką, veikiantį į elektroninę posistemę. Optiniai spektroskopiniai tyrimai buvo atlikti kombinuotu spektroskopinės elipsometrijos ir atspindžio spektroskopijos metodu, paremtu darbe pasiūlyta inkaro lango duomenų analizės schema. Naudotas spektroskopinių tyrimų metodas įgalino atskleisti patikimus ZnMgRE optinio laidumo spektrus plačioje, 0.01 – 6 eV, spektrinėje srityje. Darbe išplėstas ZnMgRE elektronų posistemės modelis, kuris anksčiau buvo pasiūlytas kvazikristalų fotoemisinio atsako analizei. Nepriklausomų Fermi paviršiaus sankirtų su Bragg’ų plokštumomis schema formuluota išplėstiniame juostiniame atvaizdavime. Teorinė optinio laidumo skaičiavimų schema, anksčiau pasiūlyta kristalinių junginių optinio laidumo skaičiavimams, šiame darbe išplėsta įskaitant įvairias Fermi lygmens padėtis pseudotarpo atžvilgiu. Teoriniai ZnMgRE optinio laidumo skaičiavimai, atlikti darbe pasiūlyto elektroninės posistemės modelio rėmuose, detaliai atkartoja eksperimentinius optinio laidumo spektrus... [toliau žr. visą tekstą]

In this Dissertation thesis the spectral theory of Schrödinger operators modeling quasicrystals in dimension one ist investigated. We allow for a large class of measures as potentials covering also point interactions. The main results can be stated as follows: If the potential can be very well approximated by periodic potentials, then the correspondig Schrödinger operator does not have any eigenvalues. If the potential is aperiodic and satisfies a certain finite local complexity condition, the absolutely continuous spectrum is absent. We also prove Cantor spectra of zero Lebesgue measure for a large class of (a randomized version of) the operator.

In the present work positron lifetime spectroscopy and coincidence spectroscopy of Doppler broadening of annihilation radiation were employed for investigations of defects in Mg alloys with icosahedral phase. Samples of WE43 alloy and WE43 alloy modified by addition of zinc were investigated. Positron trapping at vacancy-like defects associated with interface between the icosahedral phase Mg3Zn6Y1 and Mg matrix was observed. Investigations of MgZnAl-based alloys were performed as well. Vacancy-like defects were not detected in MgZnAl- based alloys by positron lifetime spectroscopy. However, coincidence spectroscopy of Doppler broadening of annihilation radiation revealed that positron trapping in the vincinity of icosahedral Mg44Zn41Al15 phase occurs. Several hypotheses ex- plaining different nature of positron trapping in WE43-based and MgZnAl-based alloys were proposed. Keywords: quasicrystals; positron annihilation spectroscopy; positron trapping; open-volume defects

Le nombre croissant de nanostructures physiques et biologiques sont caractérisées par l'ordre non-cristallin et par les propriétés physiques et biologiques non-conventionnels. Parmi ses systèmes il faut distinguer les capsides virales. Ces coquilles solides qui sont formées par un certain nombre dec opies de la même protéine protègent le virus des agressions et facilitent le processus d'infection de la cellule hôte. La distribution des positions de protéines dans une capside est très régulière et montre un degré très élevé d'ordre, aussi bien orientationnel que positionnel. Les capsides virales de topologie sphérique possèdent la symétrie icosaédrique compatible avec l'ordre cristallin local, mais incompatible avec la symétrie cristalline globale et interdite dans les structures périodiques.Ici, sur l'exemple des Papovavirus, nous montrons l'existence d'un nouveau type d'organisation qui résulte dans l'ordre quasicristallin pentagonal chiral de protéines dans des capsides de topologie sphérique et géométrie dodécaédrique. La formation de cet ordre est décrite dans le cadre de la théorie de Landau de cristallisation. Les particularités de la structure sont élucidées grâce à la théorie d'élasticité des quasicristaux comme le résultat de la déformation phason nonlinéaire.La généralisation de la théorie de Landau de cristallisation que nous proposons permet également de décrire des structures quasicristallines octogonales et décagonales grâce à la minimisation contrainte de l'énergie libre, et donne un nouveau sens physique à la notion de « fenêtre de projection » utilisée dans la cristallographie multidimensionnelle. / A growing number of physical and biological nanostructures are characterized by non-crystallineorder and by unconventional physical and biological properties. Among these systems one can distinguish viral capsids. These solid shells formed by a certain number of copies of the same protein protect viruses from aggressions and facilitate infection of the host cell. Protein distributionin a capsid is quite regular and shows high degree of order, both orientational and positional. Viral capsids with spherical topology have icosahedral symmetry compatible with local crystalline orderbut incompatible with the global one and forbidden in periodic structures.Here, on the example of Papovaviruses we show the existence of a new type of organization whichresults in the chiral pentagonal quasicrystalline order of proteins in capsids with spherical topology and dodecahedral geometry. The formation of this order is described in the frame of the Landau theory of crystallization. The theory of elasticity of quasicrystals is used to show that the structure peculiarities result from the non-linear phason strain.Generalization of the proposed Landau theory of crystallization allows us to describe octagonal and decagonal quasicrystalline structures using constrained minimization of the free energy, thus giving a new physical sense to the « projection window » notion used in multi-dimensionalcrystallography.