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1
Schmehr, Julian Leonard. "Incommensurate magnetism in UAu2." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/17958.
Full textAbstract:
The aim of this thesis was to identify a candidate material for spin-triplet superconductivity with a two-component order parameter. This unconventional superconducting state is thought to allow for exotic quantum states such as Majorana fermions. A wide survey was taken into potential candidate materials, and UAu2 was chosen for in-depth investigation. This little-studied hexagonal heavy fermion compound's unusual resistivity behaviour, combined with a series of interesting features in magnetisation and heat capacity, make it an extremely interesting material to study. The phase diagram of UAu2 was determined with measurements of heat capacity, resistivity, magnetisation and magnetoresistance on the first single crystalline samples of this material. No superconductivity was detected. Instead, a range of magnetic phase transitions were observed, which were further investigated with muon-spin relaxation experiments and time-of- ight neutron powder diffraction. UAu2 was found to undergo a transition to an incommensurate antiferromagnetic state (q1 = (1=3; 1=3; δ)) below TN = 43:5 K, but then develops signatures of weak ferromagnetism below T = 20 K. The ferromagnetism coincides with a 2q magnetic structure, with a coexistence of q1 and q2=(1/3,1/3,0). The magnetic structures of both phases were found to be most likely amplitude-modulated, with moments aligned along the crystallographic c-axis. A transition to a ferromagnetic state was observed in magnetic fields applied parallel to the c-axis. TN was found to remain almost constant in applied magnetic fields up to 9 T, while hydrostatic pressures of up to 6 kbar weakly suppress the antiferromagnetic transition temperature. The field-induced transition was found to be strongly pressure-dependent, shifting to higher applied fields with increasing pressure. The residual resistivity of UAu2 samples prepared by both the Czochralski method and quenching from the melt is relatively large, which may inhibit Cooper pairing and hence may be the reason for the absence of superconductivity in the samples investigated. Solid-state electrotransport (SSE) equipment was developed, which can induce the motion of a crystal's constituents and thereby lead to vastly improved sample quality. Refinement of UAu2 samples with SSE could be a further step in the search for spin-triplet superconductivity in this material.
2
Leung, H. T. "The incommensurate phases in intermediate plagioclase feldspars." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360914.
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3
Bell, S. C. "Scaling theory of non-linear and incommensurate systems." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376893.
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4
Atkinson, A. J. "The role of strain in incommensurate plagioclase feldspars." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596217.
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Using a novel seven-circle X-ray diffractometer with an area sensitive detector, the three-dimensional shape and the intensity of a pair of satellite reflections from an incommensurate sample (An65) was followed as a function of temperature. A large displacive component was found, in contrast to the widely accepted hypothesis that the incommensurate structure is a consequence solely of competing Al/Si ordering schemes. The presence of diffuse satellites in precession photographs of a highly disordered volcanic sample supports this result. On a mesoscopic length scale, domains of perfect periodic antiphase boundaries are seen in the TEM, delimited by rings of defects. The domain size is strongly composition dependent, rising to several thousand Å at An71, and falling to zero at ~An30, possibly indicating the compositional limit of the e2 structure. Infrared spectroscopy was used to probe the microstructural variations in natural and heat-treated plagioclase series. In comparing the macroscopic strain (cosg from lattice refinements) with a measure of local strain, w, the two incommensurate phases show different behaviour, with the e1 phase extrapolating to anorthite, and e2 to disordered albite. On this length scale, the behaviour of the e1 samples is indistinguishable from the I⁻¹ phase. Order parameter values for I⁻¹ ordering are proposed from the e1 structure as a result of this work and extrapolate to zero between An40 and An50. The autocorrelation function is applied to the spectra and used to generate a local order parameter which is found to scale well with previous measurements of enthalpy of solution. Experiments were also performed on the similar incommensurate structure found in synthetic anorthites, in which high degrees of short range order were found even in the macroscopically disordered state. The two sets of data form single trends as functions of degree of order.
5
Chao, Mao-Hsun. "New insights into structural properties of incommensurate inclusion compounds." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274597.
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6
Shaw, Jeremy John Arthur. "The form and origin of incommensurate structures and polytypes." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293875.
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7
Niestemski, Liang Ren. "Incommensurate Valence Bond Density Waves in the Glassy Phase of Underdoped Cuprates." Thesis, Boston College, 2011. http://hdl.handle.net/2345/2626.
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Thesis advisor: Ziqiang WangOne of the most unconventional electronic states in high transition temperature cuprate superconductors is the pseudogap state. In the temperature versus doping phase diagram, the pseudogap state straddles across the antiferromagnetic (AF) state near half filling and the superconducting (SC) dome on the hole doped side above the transition temperature Tc. The relationship between the pseudogap state and these two well known states - the AF state and the SC state is believed to be very important for understanding superconductivity and the emergent quantum electronic matter in doped Mott insulators. The pseudogap is characterized by the emergence of a soft gap in the single-particle excitation spectrum in the normal state in the temperature range between Tc and a characteristic temperature T*, i.e. Tc < T < T*. The most puzzling feature of the pseudogap is the nodal-antinodal dichotomy. Observed by ARPES in momentum space, the Fermi surface is gapped out in the antinodal region leaving a Fermi arc of gapless excitations near the nodes. Whether the pseudogap is an incoherent superconducting gap (onegap scenario) or it is a different gap governed by other mechanisms, other than superconductivity, (two-gap scenario) is still under debate. In this thesis I study the particle-particle channel and the particle-hole channel of the valence bond fluctuations away from half filling. Based on a strong-coupling analysis of the t-J model, I argue that the superexchange interaction J induced incommensurate bond centered density wave order is the driving mechanism for the pseudogap state. Low energy density of states (DOS) are eliminated by multiple incommensurate scatterings in the antinodal region at the Fermi level. I show that the interplay between the incommensurate bond centered d-wave density wave instability and the intrinsic electronic inhomogeneity in real cuprate materials is responsible for the observed pseudogap phenomena. Utilizing the spatially unrestricted Gutzwiller approximation, I show that the off-stoichiometric doping induced electrostatic disorder pins the low-energy d-wave bond density fluctuations, resulting in a VBG phase. The antinodal Fermi surface (FS) sections are gapped out, giving rise to a genuine normal state Fermi arc. The length of the Fermi arc shrinks with underdoping below the temperature T* determined by thermal filling of the antinodal pseudogap. Below Tc, the d-wave superconducting gap due to singlet pairing coexists and competes with the VBG pseudogap. The spatial, momentum, temperature and doping dependence of these two gaps are consistent with recent ARPES and STM observations in underdoped and chemically substituted cuprates. The temperature versus doping phase diagram captures the salient properties of the pseudogap phenomena and provides theoretical support for the two-gap scenario. In addition to resolving the complexities of the quantum electronic states in hole-doped cuprates, my unified theory elucidates the important role of the interplay between the strong electronic correlation and the intrinsic electronic disorder in doped transition metal oxides
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
8
Johnson, Stuart Thomas. "X-ray scattering studies of the incommensurate high-Tc superconductor Bi2Sr2CaCu2O8+δ." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/15108.
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The compound Bi2Sr2CaCu2O8+δ is of special interest for two reasons: it is an important member of the family of cuprates who possess superconducting transitions at high temperatures, and it is an example of the class of layered compounds whose structures are distinguished by incommensurate modulation. The unique normal state and superconducting properties of the cuprates are intricately linked to their far from ideal disordered structures. The additional incommensurate nature of some compounds has greatly hampered the understanding of their novel behaviour. This thesis describes single crystal studies of Bi2Sr2CaCu2O8+δ using x-ray scattering techniques as a tool for establishing in detail those structural features of significance to the behaviour of this compound as a superconductor, and those of importance to its nature as an incommensurate. The thesis starts with the characterisation of the variations between crystals grown, using flux and floating zone methods, by four separate research groups. The inclusion of impurities is found to be a feature of flux grown crystals. The nature of the incommensurate modulation is also clarified, and defects associated with it are identified. The fundamental properties of the modulation are investigated by studying in situ the response of the structure to high temperature. It is demonstrated that the modulation is strongly pinned and that the incommensurate period of the modulation is not a continuous function of oxygen content; a possible oxygen deficient high temperature phase is tentatively identified. The inert nature of the incommensurability to temperature is also established at low temperature, down to 20K, limiting any possible direct involvement of the modulation in the superconducting transition. Oxygen content, on the other hand, is known to hold a major influence over both normal state and superconducting properties, and a study is made of the effects of nitrogen and oxygen annealing treatments. The results reveal modifications in microstructure associated with oxygen ordering, a result of potential importance to the understanding of transport properties.
9
Moss, George W. "Mathematical Models of the Alpha-Beta Phase Transition of Quartz." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28607.
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We examine discrete models with hexagonal symmetry
to compare the sequence of transitions with the
alpha-inc-beta phase transition of quartz. We
examine a model by Parlinski which employs
interactions of nearest and next-nearest neighbor
atoms. We numerically determine the configurations
which lead to minimum energy for a range of
parameters. We then use Golubitsky's results on
systems with hexagonal symmetry to derive the
bifurcation diagram for Parlinski's model. Finally,
we study a large class of modifications to
Parlinski's model and show that all such
modifications have the same bifurcation picture
as the original model.Ph. D.
10
Allen, Patryck Kevyn Kidd. "Structural studies of lead-free piezoelectrics with the fresnoite structure type." Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/11986.
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The lead free piezoelectric fresnoite A2M3O8 (A = Ba, Sr, K, Cs; M = Ti, V, Si, Ge) modulated structure type has been investigated owing to its potential to exhibit excellent piezoelectric response coefficients. Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8 end members in addition to members of the Ba2xSr2-2xTiSi2O8, Ba2xSr2 2xTiGe2O8, Ba2TiGe2ySi2 2yO8, and BaSrTiGe2ySi2 2yO8 series were synthesised and characterised using a combination of variable temperature diffraction techniques. The Ba2TiSi2O8 and Sr2TiSi2O8 modulated structures at ambient temperature were characterised using neutron powder diffraction for the first time. Variable temperature synchrotron X ray diffraction data showed a new means of identifying the incommensurate to prototypic structural phase transition at 433 K. Resonant ultrasound spectroscopy has shown coupling between the elastic moduli and structural changes in fresnoite samples. Polycrystalline Sr2TiSi2O8 samples were shown to undergo a first order phase transition from a two phase mixture of incommensurately modulated tetragonal and orthorhombic phases to a single incommensurately modulated orthorhombic phase that is complete by 567 K. The proportion of the orthorhombic phase Sr2TiSi2O8 samples was shown to slowly decrease on cooling to 125 K. The Sr2TiSi2O8 structure was also shown to undergo an additional phase transition from the incommensurately modulated orthorhombic phase to a tetragonal phase at 1323 K for the first time. The inclusion of barium or germanium into the Sr2TiSi2O8 structure was shown to suppress the formation of the orthorhombic phase at ambient temperature and elevated temperatures. New phase diagrams for the Ba2xSr2-2xTiSi2O8 and Sr2TiGe2ySi2 2yO8 systems summarise the phase transitions investigated. The intrinsic piezoelectric coefficients were calculated to be approximately 5 pm V 1 and 27 pm V 1 for polycrystalline samples of Ba2TiSi2O8 and Sr2TiSi2O8 respectively and compared to common piezoelectric materials.
11
Drees, Jan Yvo. "Magnetism in layered Nickelates and Cobaltates." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-192533.
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Single layered perovskites with the chemical formula La2−xSrxTO4 (T = transition metal) exhibit a variety of intriguing ordering phenomena. The most outstanding is the occurrence of high temperature superconductivity in La2−xSrxCuO4, which can be considered as the prototype system for the more complex cuprates. Some cuprates show incommensurate static charge order at low temperatures [38–40]. For others it is believed that charges are dynamically correlated [39, 147, 259]. Such effects are difficult to measure if the charges fluctuate.
In contrast to the cuprate La2−xSrxCuO4 the isostructural nickelates and cobaltates remain insulating over a wide doping range [112, 134, 135, 138]. While incommensurate charge stripe order is long known for the nickelates, recently also evidence for charge stripes in cobaltates has been published [174].
Single crystal rods, with ≈10cm length and ≈0.8cm diameter, have been grown by the traveling solvent floating zone technique using an optical four mirror furnace. We investigated strontium doped nickelates in the range 0.15 ≤ x ≤ 0.22. In addition, also co-doped nickelates have been investigated. A large number of samples with different doping concentrations enabled us to systematically characterize the sample properties. Powder X-ray diffraction measurements were used to determine the lattice parameters. For the nickelates we could confirm the doping dependence of the lattice constants reported in literature [202].
The main interest for the cobaltate system was in the strontium doping range 1/3 ≤ x ≤ 1/2. It was previously reported that the ab-lattice parameter exhibits an anomalous peak around a Sr doping x ≈ 1/3 [140]. We could not confirm such an anomaly for our samples and, instead, we observe a strictly monotonic doping dependence of the lattice parameters which we attribute to the close to perfect stoichiometry of our samples.
Samples with the 214-layered perovskite structure can be synthesized over a wide range of oxygen off-stoichiometry. However, the oxygen content can have similarly strong influence on the sample properties as strontium doping. It is therefore essential for data interpretation to determine the oxygen off stoichiometry. EDX and WDX measurements were used to confirm the oxygen content in our nickelates to be nearly stoichiometric. The oxygen content determination of the cobaltates is somewhat more difficult. Thermogravimetry measurements in a flow of Ar/H2 confirmed a nearly stoichiometric oxygen content δ in La2−xSrxCoO4+δ for all samples.
We used neutron diffraction measurements to determine the magnetic order in our nickelate samples. In stripe ordered nickelates a small titanium co-doping of the order of 5% is suficcient to supress the incommensurate magnetism and restore antiferromagnetic order. Within the series of zinc co-doped nickelates three samples exhibit an incommensurability epsilon ≈ 1/8, indicating the stabilization of an intermediate stripe pattern with an eightfold unit cell. Compared to the epsilon ≈ 1/3 regime the correlation length is greatly reduced.
The magnon dispersion of two samples within the intermediate stripe phases with epsilon ≈ 1/8 and epsilon ≈ 1/4 has been measured with neutron spectroscopy. The observed dispersion neither resembles the one in the undoped nor the 1/3 strontium doped samples. Despite the amount of disorder in our co-doped nickelate materials there are no clear signs for the emergence of hourglass spectra which is most likely caused by a strong exchange interaction across the holes.
We investigated the charge and magnetic order in the incommensurate regime of La2−xSrxCoO4 with doping 0.33 ≤ x ≤ 0.5 by elastic neutron scattering and hard X-ray synchrotron measurements. In contrast to the established opinion that this phase is characterized by charge stripe order we were able to show that no charge stripes are present. Instead we found that checkerboard charge order, which is most stable at x = 1/2, persists to a much lower doping than previously thought. The absence of charge stripes is also in agreement with the dispersion of the top most Co-O bond stretching phonon mode. Charge order can induce an anomaly in this branch according to the modulation vector ~q. We observed a softening at ~q = (1/2 1/2 0), which is consistent with our expectations for a checkerboard charge ordered phase.
Inelastic neutron measurements revealed an additional high energy part of the hourglass dispersion which has not been reported so far. The entire lowenergy spin excitations that belong to the classical hour-glass dispersion are mostly in-plane excitations, the newly discovered high-energy magnon mode arises from out-of-plane excitations. The resemblance between the low energy excitations below the neck of the hourglass with the excitations in La1.5Sr0.5CoO4 and similarly between the high energy excitations with those observed in La2CoO4 suggests that the observed dispersion is not a single dispersion, but instead consists of two dispersions with distinct origin. In this model the low-energy dispersion arises mainly from magnetic excitations of hole doped regions and the high-energy part would be connected to magnetic excitations within the undoped islands.
The absence of charge stripe order in the insulating cobaltates in combination with an unmagnetic low spin state for Co+3 requires a different explanation for the presence of incommensurate magnetic order. We propose a picture on the basis of the ideal checkerboard charge order of the half doped reference system. Decreasing the strontium concentration requires the replacement of Co+3 by Co+2, effectively resulting in the competition between the antiferromagnetic order of the undoped and the antiferromagnetic order of the half doped compound. The induced frustration can be released by a twisting of magnetic moments away from their antiferromagnetic orientation, ultimately leading to the observed incommensurate magnetic order.
12
Chaimayo, Wanaruk. "Synthesis and high-pressure structural studies of bismuth nanoparticles." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7951.
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Nanomaterials (NMs) are materials in which the size of at least one dimension is less than 100 nm. Examples include quantum dots, nanoparticles, “Buckminsterfullerene (C60)”, carbon nanotubes, graphene and TiO2 thin films. Many research groups have investigated the properties of NMs, and they have reported that some of them are clearly different to those of the bulk materials, and depend on the size of the NMs. Examples include melting temperatures, phase transition pressures, fluorescence spectra, catalytic properties and magnetic properties. Recently, a high-pressure study of Te nano-cylinders revealed compressibility effects that are different to those observed in bulk-Te. Although this study reported an elevation of phase transition pressure compared to the bulk, the authors did not investigate the structures of the high-pressure phases, and it is unclear whether the incommensurate phase found at high pressures in bulk-Te was observed or not. Indeed, it is completely unknown whether the incommensurate phases observed in a number of elements at high pressure also exist in nanoparticle samples of the same materials. The search for, and study of, such phases forms the subject of this thesis. Initial studies of commercial selenium nanoparticles (nano-Se) revealed that the incommensurate phase of bulk selenium (Se-IV) is also found in nano-Se. The transition pressures in nano-Se are slightly higher than those of bulk-Se. However, the nano-Se samples were subsequently found not to have the sizes, shapes, and properties claimed by the vendor, which was confirmed by transmission and scanning electron microscopy. Further commercial samples of nano-Se and nano-Bi were also found to be of extremely poor quality. It was clear, therefore, that a detailed study of incommensurate phases in NMs would require us to make our own samples. Bismuth nanoparticles (nano-Bi) with dimensions 51(6), 52(15), 92(13), 128(45), and 138(27) nm have been successfully synthesised by the author in collaboration with the Hybrid Nano Collods group at the University of St. Andrews. On compression, the nano-Bi samples were found to have the same order of phases Bi-I, Bi-II, Bi-III, and Bi-V and phase transitions as found in bulk-Bi, but were found to exhibit larger phase coexistence. The phase transition pressures on pressure increase were higher than those of the bulk materials, and the smaller the diameter of nano-Bi, the higher the phase-transition pressure. This behaviour is similar to, but more extreme than, that found in CdSe nanoparticles. The incommensurate Bi-III structure has been found in nano-Bi under increases in pressure. However, the di↵raction patterns from Bi-III contain additional unaccounted-for peaks, and this phase is referred to as complex Bi-III. The Debye- Scherrer rings from complex Bi-III are smooth, and do not exhibit the spottiness observed in the diffraction patterns of Bi-III obtained from bulk-Bi. This enables full Rietveld refinement of Bi-III in the nano-samples. Complex Bi-III exists from 3 GPa up to 30 GPa, compared to the stable range of only 2.7 to 7.7 GPa of Bi-III in the bulk material. While such a large range of pressure enables the structure of nano-Bi-III to be studied over a much wider pressure range than bulk-Bi-III, such studies were hampered by the existence of the unaccounted-for peaks. In order to get clean, single-phase patterns of Bi-III, samples of this phase were first prepared on pressure decrease from the higher-pressure Bi-V phase, before recompressing them. Single-phase samples of Bi-III were obtained and were found to be stable up to 14-18 GPa. However, because of phase coexistence, diffraction peaks from Bi-III were still visible at pressures as high as ~30 GPa, which is ~3 times larger than the upper limit pressure of existence of bulk-Bi-III. On pressure re-increase, nano-Bi-III has a higher bulk modulus than bulk-Bi-III. The bulk modulus was found to be size-dependent as it is higher when size decreases. Moreover, nano-Bi has a smaller value of the incommensurate wave vector, which is almost pressure independent, but is found to be particles size dependent. The incommensurate wave vector thus becomes another of the structural and physical properties of nanomaterials that is found to be sample-size dependent.
13
Terashima, Taichi. "Systematic Studies on Electronic and Magnetic Properties of Incommensurate Layer Compounds(RES)xNbS[2](RE=rare-earth metals; x=1.2,0.6)." 京都大学 (Kyoto University), 1993. http://hdl.handle.net/2433/168945.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第5437号
理博第1485号
新制||理||828(附属図書館)
UT51-93-J492
京都大学大学院理学研究科化学専攻
(主査)教授 斎藤 軍治, 教授 小菅 皓二, 教授 板東 尚周
学位規則第4条第1項該当
14
Bouchard, Alexandre. "Composés inter-halogènes sous pression: étude des transformations structurales dans le monobromure d’iode sous forme dense." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20697.
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La famille des composés halogènes et inter-halogènes représentent des solides moléculaires adoptant des phases denses communes avec des solides moléculaires diatomiques comme l’azote et l’hydrogène. Parmi les transformations structurales et électroniques induites sous haute pression et observées dans ces solides, on note, entre autres, la dissociation moléculaire et la métallisation. De plus, l’étude des phases denses de l’iode a permis récemment l’observation d’une structure cristalline possédant une modulation dite incommensurable, c’est-à-dire une modulation possédant une périodicité différente de celle de la structure cristalline, jetant ainsi une lumière nouvelle sur le processus de dissociation moléculaire dans les solides halogènes. Dans ce mémoire, on propose d’étudier les changements structuraux dans monobromure d’iode (IBr), un composé inter-halogène possédant des propriétés structurales semblables à celles de deux composés halogènes, soit l’iode (I2) et le brome (Br2) sous leur forme solide. Des expériences de diffraction des rayons X de poudres en utilisant un rayonnement synchrotron ont été réalisées à température ambiante sur l’IBr en variant la pression jusqu’aux environs de 60 GPa. La nature chimique particulière du composé IBr a nécessité la mise au point de techniques de chargement d’échantillon destinées à préserver l’intégrité chimique de la substance utilisée. On rapporte également l’observation d’une phase de l’IBr présentant une modulation incommensurable. Les phases observées dans l’IBr permettent d’établir des parallèles avec les phases denses rapportées dans I2 et Br2 par le biais d’un modèle phénoménologique décrivant la séquence structurale des solides halogènes sous forme condensée.
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Graf, Christian. "Untersuchungen zu kommensurablen und inkommensurablen Überstrukturen der Lanthanoidpolychalkogenide LnQ2–[delta] sowie deren thermochemischen und physikalischen Eigenschaften." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1225387172786-08876.
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Im Rahmen dieser Arbeit wurden thermodynamische Modellationen, Synthesen und Strukturuntersuchungen zu Lanthanoidpolysulfiden und den selenärmeren Lanthanoid-polyseleniden durchgeführt. Bereits bekannte thermodynamische Daten der Lanthanoidpolysulfide, welche durch Gesamtdruckmessungen ermittelt wurden, konnten genutzt werden, um neue Synthesewege zur Darstellung der Lanthanoidpolysulfide thermodynamisch zu modellieren. Im Rahmen dieser Modellierungen wurde für Praseodym exemplarisch gezeigt, dass ein chemischer Gasphasentransport der Polysulfide unter Zugabe von Br2(l) und unter der Ausbildung des Transportmittels SBr2(g) möglich ist. Des Weiteren konnte die Synthese der Verbindungen LnS1.9 (Ln = La – Nd, Gd) unter Verwendung von HgS als Sulfiddonor durchgeführt und anhand der entwickelten elektrochemischen Spannungsreihe anorganischer sulfidischer Festkörper sowie weiterführender thermodynamischer Rechnungen rationalisiert werden. Die durch thermodynamische Rechnungen optimierten Synthesen lieferten Kristalle guter bis hervorragender Qualität, welche durch anschließende Röntgen¬beugungsexperimente charakterisiert wurden. Anhand dieser Daten konnten die Kristallstrukturen einer Vielzahl von Lanthanoidpolychalkogeniden LnQ2–δ (Ln = La – Ho, Y; Q = S, Se; 0 £ £ 0.15) gelöst und verfeinert werden. Die Strukturtypen, welche im Rahmen dieser Arbeit für die Lanthanoidpolychalkogenide gefunden wurden, sind der CeSe2-Typ, der CeSe1.9-Typ, eine niedersymmetrische Form des GdSe1.875-Typs und eine inkommensurabel modulierte Variante des PrSe1.85-Typs. Da es sich bei allen beschriebenen Verbindungen um Überstrukturen des ZrSSi-Typs handelt, wurden zur Veranschaulichung dieser Tatsache Bärnighausen-Stammbäume für die gefundenen Strukturtypen aufgestellt. Anhand dieser Stammbäume wurde illustriert, wie sich die Atomlagen der niedersymmetrischen Überstrukturen aus denen des hochsymmetrischen Aristotyps ableiten lassen.
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Lind, Hanna. "Modulations in Intermetallic Families of Compounds." Doctoral thesis, Stockholm : Dept. of Inorganic Chemistry, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-312.
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Bellec, Ewen. "Study of charge density wave materials under current by X-ray diffraction." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS437/document.
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Ce manuscrit a pour sujet principal la diffraction par rayons X des matériaux ondes de densité de charges (ODC). Nous avons étudié le cristal quasi-1D NbSe3 ainsi que le quasi-2D TbTe3. Plusieurs grands instruments ont été utilisés pour cette étude, le synchrotron ESRF de Grenoble sur la ligne ID01 ainsi que le laser à électron libre LCLS à Stanford. Premièrement, grâce à la cohérence du faisceau X à LCLS, nous avons pu observer une perte de cohérence transverse dans NbSe3 lors de l’application d’un courant électrique au-dessus d’un certain seuil ainsi qu’une compression longitudinale de l’ODC. Ensuite, à l’ESRF, nous avons utilisé un faisceau X focalisé au micromètre par une Fresnel zone plate pour scanner l’ODC localement par diffraction sur NbSe3 puis ensuite sur TbTe3. Lorsqu’un courant est appliqué sur l’échantillon, nous avons observé une déformation transverse indiquant que l’ODC est bloquée au niveau de la surface de l’échantillon dans NbSe3. Dans le cas de TbTe3, l’ODC tourne sous courant présentant un cycle d’hystérésis lorsque le courant passe continument de positif à négatif. Nous avons aussi pu constater dans plusieurs régions, toujours pour TbTe3, la création de défauts d’irradiation localisés induisant une compression-dilatation de l’ODC. Dans une dernière partie théorique, nous montrons comment la théorie du transport électrique de l’ODC par un train de solitons portants chacun une charge ainsi que la prise en compte du blocage de l’ODC sur la surface de l’échantillon que nous avons vu expérimentalement permet de comprendre plusieurs mesures de résistivité en fonction des dimensions de l’échantillon trouvées dans la littérature. Nous présentons ensuite plusieurs idées pour expliquer du blocage de l’ODC sur les surfaces au niveau microscopique et proposons l’hypothèse d’une ODC commensurable en surface (et incommensurable dans le volume)The main subject of this manuscript is the X-ray diffraction of charge density wave (CDW) materials. We studied the quasi-1D NbSe3 crystal and the quasi-2D TbTe3. Several large instruments facilities were used for this study, the ESRF synchrotron in Grenoble on the ID01 line and the LCLS free electron laser in Stanford. First, thanks to the coherence of the X-beam at LCLS, we were able to observe a loss of transverse coherence in NbSe3 when applying an electrical current above a certain threshold as well as a longitudinal compression of the CDW. Then, at the ESRF, we used an X-ray beam focused on the micrometer scale by a Fresnel zone plate to scan the CDW locally by diffraction on NbSe3 and on TbTe3. When a current is applied to the sample, we observed a transverse deformation indicating that the CDW is pinned on the sample surface in NbSe3. In the case of TbTe3, the CDW rotates under current showing a hysteresis cycle when one is continuously changing from positive to negative current. We have also observed in several regions, in TbTe3, the creation of localized irradiation defects inducing a compression-dilation of the CDW. In a last theoretical part, we show how the theory of electric transport in the CDW state by a train of charged solitons, as well as taking into account the CDW pinning on the surface of the sample that we have seen experimentally, allows us to understand several resistivity measurements, found in the literature, made on samples with different dimensions. Finally, we present several ideas for an explanation of the CDW pinning at the surfaces on a microscopic level and propose the hypothesis of a commensurate CDW on the surface (and incommensurate in volume)
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Barré, Sylvie. "ETUDE DE LA PHASE INCOMMENSURABLE DE Ba2NaNb5O15 PAR MICROSCOPIE ELECTRONIQUE : influence des defauts sur la transition." Toulouse 3, 1987. http://www.theses.fr/1987TOU30244.
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Apres une presentation des proprietes generales des systemes incommensurables, rappel des problemes particuliers poses par la phase incommensurable de ba::(2)nanb::(5)o::(15). Etude experimentale par microscopie electronique, entre la temperature ambiante et 350c. Le comportement observe peut etre explique en considerant que vers 230c, la phase incommensurable est constituee d'un melange de deux phases metastables. En utilisant l'effet de memoire, ces phases ont pu etre stabilisees et les auteurs ont ainsi obtenu des precisions sur leurs structures. Cet effet de memoire est interprete par la presence de defauts qui interagissent avec la modulation modifiant les stabilites relatives des deux phases. Etude de ce dernier point en creant des defauts par irradiation par des electrons (2 mev)
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Mogeon, François. "Propriétés statiques et comportement irréversible de la phase incommensurable du quartz." Grenoble 1, 1988. http://www.theses.fr/1988GRE10132.
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Mesure de la variation, en fonction de la temperature, des grandeurs caracteristiques de la phase incommensurable: dilatation, module et direction du vecteur d'onde de modulation. Interpretation dans le cadre d'une theorie phenomenologique. La resolution de la methode a permis l'observation directe d'une phase mono q en l'absence de contraintes exterieures. Une correlation entre la variation du vecteur d'onde de modulation et celle de la birefringence en fonction de la temperature a ete etablie par diffraction de rayons gamma couplee avec mesure de birefringence
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Storeck, Gero [Verfasser], Claus [Akademischer Betreuer] Ropers, Claus [Gutachter] Ropers, and Stefan [Gutachter] Mathias. "Non-equilibrium structural Dynamics of incommensurate Charge-Density Waves : Diffractive Probing with a micron-scale ultrafast Electron Gun / Gero Storeck ; Gutachter: Claus Ropers, Stefan Mathias ; Betreuer: Claus Ropers." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1213096286/34.
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Behrendt, Karsten. "Der Einfluss von Defekten auf das Schaltverhalten ferroelektrisch modulierter Substanzen." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0028-873E-C.
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Smith, Jeannette Ward. "Being incommensurable/incommensurable beings ghosts in Elizabeth Bowen /." unrestricted, 2006. http://etd.gsu.edu/theses/available/etd-04282006-181909/.
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Thesis (M.A.)--Georgia State University, 2006.Title from title screen. Marilynn Richtarik, committee chair; Calvin Thomas, Margaret Mills Harper, committee members. Electronic text (84 p.) : digital, PDF file. Description based on contents viewed Apr. 17, 2007. Includes bibliographical references (p. 75-84).
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Smith, Jeannette Ward. "Being Incommensurable/Incommensurable Beings: Ghosts in Elizabeth Bowen’s Short Stories." Digital Archive @ GSU, 2006. http://digitalarchive.gsu.edu/english_theses/11.
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I investigate the ghosts in Elizabeth Bowen’s short stories, “Green Holly” and “The Happy Autumn Fields.” By blending psychoanalytic feminism and social feminism, I argue that these female ghosts are the incommensurable feminine—a feminine that exceeds the bounds of phallocentric logic and cannot be defined by her social or symbolic manifestations. An analysis of Bowen’s ghosts as actual ghosts is uncharted territory. Previous Bowen critics postulate that Bowen’s ghosts are imaginary figments or metaphors. These critics make Bowen’s stories “truthful” representations of the world, but, as such, Bowen’s ghosts become representations of the world’s phallocentric order. In contrast, I argue that these stories adopt a mestiza consciousness. Gloria Anzaldùa postulates that through a subaltern perspective developed outside of western logic, the mestiza reclaims the supernatural that exists outside of the masculine, symbolic order. The female ghosts are the feminine that Luce Irigaray explains, “remain[s] elsewhere” (76) as they live incommensurably in an alternate supernatural realm, disrupting phallic logic.
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Fagot-Revurat, Yannick. "Étude par résonance magnétique nucléaire en champ magnétique intense du composé Spin-Peierls CuGeO3." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10003.
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Cette these est consacree a l'etude par rmn du diagramme de phase sous champ magnetique du compose spin-peierls cugeo#3 compose de : - la phase magnetique uniforme caracterisee par des correlations antiferromagnetiques uni-dimensionnelles (u, t > t#s#p = 14. 2 kelvin) - la phase dimerisee caracterisee par une dimerisation structurale et un etat fondamental singulet non-magnetique (d, t < t#s#p, h < h#c = 12. 5 t) - la phase haut champ caracterisee par une modulation incommensurable de la position des atomes et de l'aimantation locale (i, t < t#c = 10 k et h > h#c). L'analyse du taux de relaxation spin-reseau (1/t#1) souligne dans la phase u la faible contribution des fluctuations antiferromagnetiques a l'approche de la transition indiquant que le modele de la chaine de heisenberg de spins s = 1/2 n'est pas suffisant pour decrire les proprietes magnetiques dans ce compose contrairement a la plupart des composes spin-peierls organiques. La decroissance exponentielle de 1/t#1 observee dans la phase d met en evidence la suppression de ces fluctuations due a l'ouverture du gap de spin-peierls (#o = 24 k si h = 0). La dependance en champ de 1/t#1 ainsi que l'elargissement des spectres rmn sous champ magnetique pour t << t#s#p montre la reduction lineaire du gap par le champ magnetique du au caractere triplet (s = 1) des excitations magnetiques caracteristiques des liquides de spins en general (chaine dimerisee, echelles de spins, chaine de haldane etc. . . ). Cet elargissement observe dans la phase d met a nouveau en evidence l'importance des interactions indirectes spin-spin (nucleaires) comme sonde de la susceptibilite antiferromagnetique statique non-locale (a q = ) dans les systemes 1d. Les formes de raie rmn dans la phase incommensurable font la preuve d'une aimantation locale modulee spatialement de periode incommensurable. Celle-ci se concentre dans des parois de domaines (solitons) separant des regions non-magnetiques proche de h#c et devient sinusoidale sous fort champ magnetique (h > 26. 5 t).
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Akkermans, Éric. "Propagation d'ondes dans les milieux désordonnés." Grenoble 1, 1986. http://www.theses.fr/1986GRE10050.
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Les phenomenes etudies font intervenir la phase de l'onde et la dimensionalite de l'espace de propagation. Dans le cas des systemes uni et bidimensionnels, les ondes subissant des collisions multiples elastiques interferent fortement et conduisent a des modes propres exponentiellement localises. Leur structure est etudiee sur la base d'un modele particulier de potentiel incommensurable. Le transport des phonons et des electrons dans les systemes unidimensionnels desordonnes a ete plus generalement caracterise
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Höglin, Viktor. "Structure-Magnetic Relationships in the Fe-Mn-P-Si System for Energy Applications." Doctoral thesis, Uppsala universitet, Oorganisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-234516.
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Demands for new, energy-efficient appliances have greatly increased in response to our growing need for a more environmentally friendly society. Magnetic refrigeration is a technique that utilizes the magnetocaloric effect, with possible energy savings of up to 30% compared to commercial gas compression refrigerators. A material appropriate for commercial magnetocaloric devices should be both cheap and non-toxic; it should also exhibit a first-order magnetic transitions close to room temperature. The magnetic properties of Fe2P-related materials can be relevant in this context, since their magnetic properties can be finely tuned through the substitution of Fe by Mn and P by Si, As, Ge or B to meet the general requirements for a magnetocaloric device. An in-depth study has therefore here been made of the structural and magnetic properties of the (Fe,Mn)2(P,Si)-system. The phase diagram of the FeMnP1-xSix-system has been carefully re-examined. It is found to contain two single-phase regions: an orthorhombic Co2P-type structure (x < 0.15) and a hexagonal Fe2P-type structure (0.24 ≤ x < 0.50). Selected compounds within the Fe2P-type region of the phase diagram have been shown to exhibit potential for use in magnetic refrigeration applications. Neutron powder diffraction has here been used to determine the magnetic structures of selected crystalline compositions within the FeMnP1-xSix-system to gain a better understanding of its magnetic properties. The Fe2P-type region is mainly ferromagnetic, but an incommensurate antiferromagnetic structure has also been identified close to the Co2P/Fe2P-type phase border for x ≈ 0.25. The so-called ''virgin effect'' in the Fe2P-type region of the FeMn(P,Si) phase diagram is found to be accompanied by an irreversible structural phase transition induced by magnetostriction. This new phase is found to be preserved during successive cooling-heating cycles. Furthermore, the magnetic properties of the substituted Fe2P-type structure changes significantly for metal:non-metal ratios away from 2:1. Such deviations could well explain the apparently conflicting structure-property relationships described in earlier literature for the FeMnP1-xSix-system.
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Pezeril, Michel. "Etude par R. P. E. Des transitions de phase paraélectrique-incommensurable et incommensurable-commensurable dans Rb2ZnCl4." Le Mans, 1990. http://www.theses.fr/1990LEMA1016.
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Snoeck, Etienne. "Phases incommensurables de la berlinite et du quartz imagees par microscopie electronique." Toulouse 3, 1986. http://www.theses.fr/1986TOU30067.
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La transition apparait vers 840 k de la transition hexagonale-rhomboedrique. Mise en evidence d'une structure triplement modulee dont les vecteurs d'onde varient en fonction de la temperature de la presence de domaines d'orientation etr de defauts propres a la phase modulee
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Arapan, Sergiu. "Understanding Physical Reality via Virtual Experiments." Doctoral thesis, Uppsala universitet, Institutionen för fysik och materialvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9314.
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In this thesis I have studied some problems of condensed matter at high pressures and temperatures by means of numerical simulations based on Density Functional Theory (DFT). The stability of MgCO3 and CaCO3 carbonates at the Earth's mantle conditions may play an important role in the global carbon cycle through the subduction of the oceanic crust. By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transformation is characterized by the change of the sp-hybridization state of carbon atom and indicates a change to a new crystal-chemical regime. By performing ab initio Molecular Dynamics simulations we show the new phase to be stable at 250 GPa and 1000K. Thus, the formation of sp3 hybridized bonds in carbonates can explain the stability of MaCO3 and CaCO3 at pressures corresponding to the Earth's lower mantle conditions. We have also calculated phase transition sequence in CaCO3, SrCO3 and BaCO3, and have found that, despite the fact that these carbonates are isostructural and undergo the same type of aragonite to post-aragonite transition, their phase transformation sequences are different at high pressures. The continuous improvement of the high-pressure technique led to the discovery of new composite structures at high pressures and complex phases of many elements in the periodic table have been determined as composite host-guest incommensurate structures. We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells and exploiting the fact that the total energy of the system is a function of structural parameters. By applying this method to the Sc-II phase, we have determined the incommensurate ratio, lattice parameters and Wyckoff positions of Sc-II in excellent agreement with the available experimental data. Moreover, we predict the occurrence of an incommensurate high-pressure phase in Ca from first-principle calculations within this approach. The implementation of DFT in modern electronic structure calculation methods proved to be very successful in predicting the physical properties of a solid at low temperature. One can rigorously describe the thermodynamics of a crystal via the collective excitation of the ionic lattice, and the ab initio calculations give an accurate phonon spectra in the quasi-harmonic approximation. Recently an elegant method to calculate phonon spectra at finite temperature in a self-consistent way by using first principles methods has been developed. Within the framework of self-consistent ab initio lattice dynamics approach (SCAILD) it is possible to reproduce the observed stable phonon spectra of high-temperature bcc phase of Ti, Zr and Hf with a good accuracy. We show that this method gives also a good description of the thermodynamics of hcp and bcc phases of Ti, Zr and Hf at high temperatures, and we provide a procedure for the correct estimation of the hcp to bcc phase transition temperature.
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Ronneteg, Sabina. "Chemical Tuning of the Magnetic Interactions in Layer Structures." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5973.
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Woods, Colin. "Investigations into the interfacial interaction of graphene with hexagonal boron nitride." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/investigations-into-the-interfacial-interaction-of-graphene-with-hexagonal-boron-nitride(de99f43b-790f-4a32-b696-060ed700a5bd).html.
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This thesis, submitted to the University of Manchester, covers a range of topics related to current research in two-dimensional materials under the title: 'Investigations into the interfacial interaction of graphene with hexagonal boron nitride.'In the last decade, two-dimensional materials have become a rich source of original research and potential applications. The main advantage lies in the ability to produce novel composite structures, so-called 'layered heterostructures', which are only a few atomic layers thick. One can utilise the unique properties of several species of crystal separately, or how they interact to realise a diverse range of uses. Two such crystals are graphene and hexagonal boron nitride. Hexagonal boron nitride has, so far, been used primarily as a substrate for graphene, allowing researchers to get the most out of graphene's impressive individual properties. However, in this thesis, the non-trivial van der Waals interaction between graphene and hexagonal boron nitride is examined. The interface potential reveals itself as a relatively large-scale, orientation-dependant superlattice, which is described in chapters 1 and 2.I In Chapter 4, the effect of this superlattice is examined by measurement of its effect upon the electrons in graphene, where its modulation leads to the creation of second and third generation Dirac points, revealing Hofstadter's Butterfly. As well as an excellent example of the physics possible with graphene, it also presents a new tool with which to create novel devices possessing tailored electronic properties. II In chapter 5, the consequential effect of the superlattice potential on the structure of graphene is studied. Results are discussed within the framework of the Frenkel-Kontorova model for a chain of atoms on a static background potential. Results are consistent with relaxation of the graphene structure leading to the formation of a commensurate ground state. This has exciting consequences for the production of heterostructures by demonstrating that alignment angle can have large effects upon the physical properties of the crystals. III In chapter 6, the van der Waals potential is shown to be responsible for the self-alignment of the two crystals. This effect is important for the fabrication of perfectly aligned devices and may lead to new applications based on nanoscale motion.
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Jacoby, Henry D. "Informing Climate Policy Given Incommensurable Benefits Estimates." MIT Joint Program on the Science and Policy of Global Change, 2004. http://hdl.handle.net/1721.1/4057.
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The determination of long-term goals for climate policy, or of near-term mitigation effort, requires a shared conception among nations of what is at stake. Unfortunately, because of different attitudes to risk, problems of valuing non-market effects, and disagreements about aggregation across rich and poor nations, no single benefit measure is possible that can provide commonly accepted basis for judgment. In response to this circumstance, a portfolio of estimates is recommended, including global variables that can be represented in probabilistic terms, regional impacts expressed in natural units, and integrated monetary valuation. Development of such a portfolio is a research task, and the needed program of work suggested.Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).
Results cited from the MIT Joint Program on the Science and Policy of Global Change were developed with the support of the US Department of Energy, Office of Biological and Environmental Research [BER] (DE-FG02-94ER61937) the US Environmental Protection Agency (X-827703-01-0), the Electric Power Research Institute, and by a consortium of industry and foundation sponsors.
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Germaneau, Eric. "Simulations d'une structure cristalline incommensurable à caractère désordonné /." [S.l.] : [s.n.], 2008. http://library.epfl.ch/theses/?nr=3877.
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Whitehall, Jonathan M. "Incommensurable times : representations of the personal and historical." Thesis, Royal College of Art, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503012.
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Boudot, Cécile. "Transitions de phase sous champ électrique dans la thiourée." Nancy 1, 1988. http://www.theses.fr/1988NAN10087.
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Étude des propriétés diélectriques de la thiourée hydrogénée par mesure de la constante diélectrique, de la polarisation, de la réponse pyroélectrique et du cycle d'hystérésis. Établissement du diagramme de phases dans le plan (E,T). Analyse théorique à partir d'une fonctionnelle d'énergie dérivée du modèle phénoménologique de Landau
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Repaux, Didier. "Transition commensurable-incommensurable pour des systèmes macroscopiques hors d'equilibre." Nice, 1987. http://www.theses.fr/1987NICE4119.
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Le travail présenté dans cette thèse a pour cadre général la formation de structures dans des systèmes hors d'équilibre. Parmi celles-ci les structures périodiques unidimensionnelles ont été récemment l'objet d'une attention particulière. Le premier chapitre est consacré à l'étude de l'apparition de telles structures sous l'influence d'une perturbation périodique spatiale extérieur. Lorsque la fréquence de la perturbation extérieure est suffisamment proche d'un multiple de la fréquence naturelle, on observe des phénomènes de résonnance. Ce problème est alors décrit par un développement de landau pour l'amplitude du mode déstabilisé. La compétition entre les deux périodicités conduit essentiellement à l'existence de structures quasi-périodiques stables. Nous présentons les deux mécanismes de base décrivant la transition d'une structure périodique vers une structure quasi-périodique : ce sont l'instabilité et la nucléation. Puis, nous présentons les deux mécanismes conduisant à l'existence de structures chaotiques représentées par une configuration aléatoire de défauts topologiquement stables. Le premier mécanisme a pour origine l'accrochage des défauts sur le réseau périodique sous-jacent. Le second mécanisme, obtenu dans le cadre de l'équation de landau, est lié à l'interaction oscillante entre défauts. Nous discutons ensuite la notion de quasi-cristaux dissipatifs unidimensionnels. Le second chapitre est consacré à l'étude de la dynamique des défauts de condimension 1. Il s'agit de défauts points dans un espace physique de dimension 1, de lignes en dimension 2, et de parois en dimension 3. Leur description ne nécessitant que la dimension d'espace transverse au défaut, une analogie avec la théorie des systèmes dynamiques permet de généraliser la notion de chaos spatial présentée sur un exemple dans le premier chapitre
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Repaux, Didier. "Transition commensurable-incommensurable pour des systèmes macroscopiques hors d'équilibre." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37609290w.
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N'Guessan, Gilbert Kouakou. "Réduction électrochimique du composé d'insertion graphite-chlorure de cobalt : étude du composé réduit graphite-cobalt." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0082.
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Le compose d'insertion du graphite c#5cocl#2#,#1#0 est utilise en cathode d'une pile au lithium. La decharge d'une telle pile conduit a la reduction en deux etapes du chlorure de cobalt insere. Le compose ainsi reduit de formule chimique moyenne c#1#1co#0#,#6##0#,#8(co cl#2)#0#,#4##0#,#2(licl)#0#,#5 contient une phase dans laquelle le cobalt est insere en 1#e#r stade
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Bziouet, Mohamed. "Influence des défauts sur la phase incommensurable du tétraméthylammonium-tétrachlorozincate." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612342t.
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Yan, Haile. "Crystal structure, martensitic transformation crystallography, mechanical and magnetocaloric performance of Ni(Co)MnIn multifunctional alloys." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0105/document.
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Les alliages à base de Ni-Mn-In ont attiré une attention considérable en raison de leurs propriétés multifonctionnelles depuis leur découverte en 2004, telles que l’effet de mémoire de forme métamagnétique (Metamagnetic shape memory effect MMSME), l'effet magnétocalorique (MCE) et l'effet de magnétorésistance (MR). Cependant, certaines connaissances fondamentales sur ces alliages manquent toujours jusqu'à présent, telles que la structure cristalline de la martensite, les caractéristiques cristallographiques de microstructure et de transition magnétostructurale. Dans cette thèse, les caractéristiques cristallographiques, les comportements mécaniques et les propriétés magnétiques des alliages Ni-Mn-In base ont été étudiés théoriquement et expérimentalement. Tout d'abord, les structures cristallines des alliages Ni-Mn-In ont été déterminées avec précision par la méthode de Rietveld dans le cadre de la théorie du superespace. Ensuite, la microstructure de la martensite, notamment l'organisation et l'interface des variantes, ainsi que les caractéristiques cristallographiques de la transformation martensitique, telles que les relations d'orientation (OR), le chemin de déformation de la transformation et la compatibilité géométrique entre l'austénite et la martensite, ont été systématiquement étudiés. Enfin, avec cette connaissance fondamentale sur les alliages Ni-Mn-In, les comportements et les mécanismes de sélection /réarrangement des variantes de martensite sous deux types de stratégies de chargement mécanique, à savoir le chargement à l'état martensitique et le chargement durant la transition structurelle, et les effets du recuit sur l'effet MCE et les pertes d'hystérésis associées ont été explorées. Les principaux résultats sont les suivants. La martensite modulé a une structure cristalline incommensurable avec la structure cristalline 6M et le groupe de superespace I2/m(α0γ)00 qui peut être approximée par un modèle de superstructure de multiplicité 3 dans l'espace à tridimensionnel. La microstructure de martensite est en forme de plaques et auto-organisée en colonies. Chaque colonie a quatre variantes d'orientations distinctes. Le maximum de 6 colonies distinctes et 24 variantes peut être généré à l'intérieur d'un grain austénitique. Bien que jusqu'à 14 types de relations de maclage sont proposées dans le cadre des théories cristallographiques de transformation martensitique, seuls trois types de relations de maclage sont généralement observés, à savoir des macles de type I, type II et composées. Les interfaces des variantes sont définies à l'échelle mésoscopique par leur plan de maclage K1 correspondant. Cependant, à l'échelle atomique, la macle de type I a une interface cohérente, alors que celles de type-II et les macles composées ont des interfaces étagées. Les deux relations d'orientations K-S et Pitsch sont appropriés pour décrire la correspondance de réseau entre austénite et martensite dans les alliages Ni-Mn-In. Cependant, le chemin de déformation lié à la relation de Pitsch est mis en évidence pour être efficace pour la déformation de la structure. Avec le chemin de transformation déterminé, le mécanisme sous-jacent de l'organisation des variantes est révélé. À travers la transformation martensitique, en dépit de l'existence d'une relativement large couche contrainte (de l'ordre de 20 nm), le plan d'habitat est bordé par une variante de martensite simple avec l'austénite plutôt que la structure généralement observée "en sandwich", ce qui suggère une relativement bonne compatibilité géométrique entre les phases correspondantes. Pour le chargement en compression à l'état martensitique, l'arrangement des variantes est réalisé par des processus de démaclage. Il est démontré que l'état de variante unique dans certaines colonies pourrait être obtenu lorsque l'orientation de chargement est située dans la zone de Facteur de Schmid (SF) positif commune pour les trois systèmes de démaclage. [...]Ni-Mn-In based alloys have attracted considerable attention due to their multifunctional properties since its discovery in 2004, such as metamagnetic shape memory effect (MMSME), magnetocaloric effect (MCE) and magnetoresistance (MR) effect. However, some fundenmental knowledge on these alloys is still missing until now, such as crystal structure of martensite, crystallographic features of microstructure and magnetostructural transition. In this dissertation, the crystallographic features, mechanical behaviors and magnetic properties of Ni-Mn-In based alloys were studied theoretically and experimentally. First, the crystal structures of Ni-Mn-In alloys were accurately determined by Rietveld method in the frame of superspace theory (Chapter 3). Then, the microstructure of martensite (Chapter 4), such as variant organization and interface structure, and the crystallographic features of martensitic transformation, such as orientation relationship (OR), transformation strain path and geometrical compatibility between austenite and martensite, were systematically studied (Chapter 5). Finally, with this fundamental knowledge on Ni-Mn-In alloys, the behaviors and mechanisms of martensite variant rearrangement/ selection under two kinds of mechanical loading strategies, i.e. loading at martensite state and loading across the structural transition, and the effects of annealing on MCE and its related hysteresis loss were explored (Chapter 6). The main results are as follows. The modulated martensite has an incommensurate 6M crystal structure with superspace group I2/m(α0γ)00 that can be approximated by a three-fold superstructure model in the three-dimensional space. The microstructure of martensite is in plate shape and self-organized in colonies. Each colony has four distinct orientation variants. The maximum of 6 distinct colonies and 24 variants can be generated within one austenite grain. Although as many as 14 kinds of twin relations are suggested in the frame of crystallographic theories of martensitic transformation, only three types of twin relations are generally detected, i.e. type-I, type-II and compound twin. Variant interfaces are defined by their corresponding twinning plane K1 at mesoscopic scale. However, at atomic scale, the type-I twin has a coherent interface, whereas type-II and compound twins have “stepped” interfaces. Both the K-S and Pitsch ORs are appropriate to describe the lattice correspondence between austenite and martensite in Ni-Mn-In alloys. However, the strain path related to the Pitsch relation is evidenced to be the effective for the structural distortion. With the determined transformation path, the underlying mechanism of variant organization is revealed. Across the martensitic transformation, despite the existence of a relative wide stressed layer (around 20 nm), the habit plane is bordered by single martensite variant with austenite rather than the generally observed “sandwich-like” structure, implying a relative good geometrical compatibility between the corresponding phases. For compressive loading at martensite, variant arrangement is realized by the detwinning process. It is evidenced that a single variant state in some colonies can be obtained when the loading orientation is located in the common positive Schmid factor (SF) zone of the three detwinning systems. For loading across the structural transition, the prestrain is obtained by variant selection in which the number of colonies is significantly reduced and the variant organization within colony is greatly changed. The SF for transformation strain path is introduced to evaluate the possible selection of variants. Heat treatment can significantly enhance the magnetic entropy change ΔSM but simultaneously increase the magnetic hysteresis loss. For ΔSM, the chemical ordered degree should play a prominent role [...]
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Bourgeois, Lydie. "Etudes structurales et dynamiques d'un composite d'inclusion incommensurable sous pression hydrostatique." Rennes 1, 2002. http://www.theses.fr/2002REN10055.
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Les changements de phase et les propriétés dynamiques du nonadécane-urée ont été étudiés par différentes techniques sous pression (P < 7kbars) : calorimétrie, diffusion Raman, Brillouin, diffusion neutronique, RMN. Le diagramme de phase présente aux basses pressions, deux lignes de transition reliant des phases orthorhombiques à la phase hexagonale haute température alors qu'à haute pression (P > 4kbars) une nouvelle phase orthorhombique gardant la métrique hexagonale apparaît. A 300 K, par diffraction neutronique, le paramètre d'incommensurabilité varie sous l'effet de la pression et une déformation différente des sous-réseaux d'alcane et d'urée est constatée au dessus de 1 kbar. Les défauts de conformation des chaînes étudiés par différentes spectroscopies montrent une variation de leur concentration qui offre d'étonnantes similarités avec la périodicité du sous-réseau d'alcane. Ils expliquent en grande partie, la translation anormalement grande des alcanes le long des canaux.
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Mogeon, François. "Propriétés statiques et comportement irréversible de la phase incommensurable du quartz." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37616580w.
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Treseder, Jill. "Bridging incommensurable paradigms : a training consultant recovering the wholeness of being human." Thesis, University of Bath, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307133.
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Wootten, Devon. "Faith and the incommensurable: from Pascal to Badiou via Kierkegaard and Kuhn." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/6016.
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This dissertation examines the way the Pythagorean conception of the incommensurable structures the assertions of subjective agency in Blaise Pascal’s Pensées (1670), Søren Kierkegaard’s Concluding Unscientific Postscript (1846), and Alain Badiou’s Being and Event (1988). The Pythagoreans coined the term “incommensurable,” alogos, to describe magnitudes that cannot emerge within a specific system of signification. Across three chapters, I extend the Pythagorean understanding of the incommensurable into the areas of philosophy, religious studies, and mathematics in order to posit the fundamental instability at the core of subjective agency. Moving from Thomas S. Kuhn’s failure to define the incommensurable logically in his Structures of Scientific Revolutions, I argue that such a conception of the incommensurable must be understood as fundamentally faith-based.
Given the fact that the incommensurable cannot emerge into signification, its existence must be posited on faith. Pascal, Kierkegaard, and Badiou each move from a faith-based assertion of the incommensurable to offer a conception of subjective agency within a specific system of signification. Thus, against the work of Bonaventura Cavalieri and Evangelista Torricelli, Pascal refigures the incommensurably infinite to establish a heterodox subjective agency within Augustinian faith-by-grace; Kierkegaard manages to navigate the incommensurability of direct communication and personal faith by effacing his pseudonym Johannes Climacus; and Alain Badiou relies on the incommensurable “event” to imagine the possibility the subject’s calling into being of the new. In each of these three texts, the incommensurable functions to guarantee the possibility of subject agency within a specific system of signification.
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Jerjini, Mehdi. "Etude des propriétés magnétiques des composés TGa6 avec T : Ce, Pr, Nd, Tb, Ho, Dy et des solutions solides Ce (Ga(1-x) Al(x))2." Grenoble 1, 1987. http://www.theses.fr/1987GRE10132.
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Etude des structures magnetiques de tga::(6) et ce(ga::(1-x)al::(x))::(2). Comportement de l'ion cerium dans cega::(6). Determination par des experiences de diffusion inelastique de neutrons du schema des niveaux d'energie de champ cristallin de l'ion cerium. Effet d'une insertion d'aluminium dans les sites du gallium de cega::(2) sur le caractere de kondo du compose et sur l'hybridation
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Delamoye, Pierre. "Propriétés spectroscopiques de l'uranium tétravalent dans la phase incommensurable du tétrabromure de thorium." Paris 11, 1985. http://www.theses.fr/1985PA112341.
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Cette thèse porte sur l’étude des propriétés spectroscopiques de U⁴⁺ dans ThBr₄. – les premières expériences d’absorption, d’émission (inconnue pour U⁴⁺) ainsi que des mesures de dichroïsme circulaire magnétique (DCM) effectuées à 4K sur des monocristaux de ThBr₄ : U⁴⁺ ont conduit à plusieurs résultats surprenants : largeur inhabituelle de certaines raies d’absorption, forme anormale de certaines autres, déplacement continu des longueurs d’onde des raies de fluorescence associées à l’excitation sélective des bandes d’absorption, signaux dichroïques complexes. Devant l’incompréhension apparente de ces résultats, on a cherché à vérifier si la structure cristalline de ThBr₄, qui était seulement connue à température ambiante, était bien la même à 4K. – la spectroscopie Raman a permis de mettre en évidence une transition de phase displacive à Tc = 95K. – la diffraction des rayons X et de neutrons sur poudre à basse température a confirmé l’existence d’une modification structurale qui en première approximation pouvait s’interpréter comme un triplement de maille le long de l’axe quaternaire c̅. – la diffraction de neutrons, sur monocristaux, a fait apparaître qu’entre 4K et 95K le cristal présente une structure modulée incommensurable avec un vecteur d’onde de modulation dirigé le long de l’axe c̅. Q̅s = 0. 0310 +̠ 0. 005 c̅x. – la diffusion élastique et inélastique de neutrons a permis de comprendre la dynamique de la transition de phase. La symétrie unique de site D₂d n’est pas conservée. L’interprétation complète du changement de symétrie du site de l’ion U⁴⁺ est reliée à l’introduction d’une phase locale ϕ₁. La symétrie varie continument d’une symétrie D₂d (ϕ₁ = 0) à une symétrie « extrême » D₂ (ϕ₁ = π/2). Les résultats d’excitation sélective et de DCM ont permis d’identifier systématiquement les niveaux d’énergie appartenant à U⁴⁺ en symétrie D₂d (ou D₂ extrême). Un jeu de valeurs de paramètres de champ cristallin pour les deux symétries a été proposé. En conclusion, cette étude a permis de donner une interprétation complète des propriétés optiques d’un ion placé dans une structure modulée incommensurableThis thesis is concerned with the study of the spectroscopic properties of U⁴⁺ in ThBr₄. – The complete visible and infrared absorption (emission) spectra of U⁴⁺ as doping ion in pure ThBr₄, as well as the magnetic circular dichroism (MCD) measurements have been examined. At liquid – He temperature the absorption spectra consist of broad absorption bands with two edge singularities. The apparently continuous character of fluorescence lines in selective excitation experiments, and the MCD profiles suggest the existence of a continuous distribution of U⁴⁺ sites in the host crystal. – Raman scattering results indicate the existence of a displacive phase transition at Tc = 95K. – X-ray and neutron powder diffraction data show additional lines which could be indexed approximately by a tripling of the unit cell along the c̅ axis. – Single-crystal neutron diffraction measurements indicate that below Tc, ThBr₄ has a displacively modulated structure, with a modulation wave vector q̅s given by: q̅s = 0. 0310 +̠ 0. 005 c̅x. – Inelastic neutron scattering leads us to understand the dynamics of the phase transition. The unique D₂d site symmetry for Th⁴⁺ (U⁴⁺) is not preserved. The complete interpretation of the change in the symmetry site of the U⁴⁺ ion may be described in terms of a local phase angle ϕ₁. The site symmetry varies continuously from D₂d (ϕ₁ = 0) to a limiting D₂ (ϕ₁ = π/2) symmetry. A parametric analysis of the U⁴⁺ energy levels in D₂d and limiting D₂ sites has been presented. In conclusion this study led us to give a complete interpretation of the optical properties of an ion embedded in an incommensurate structure
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Ait, Yakoub Nouara. "Etude par résonance paramagnétique électronique de la transition de phase normale incommensurable dans ThCl4." Le Mans, 1987. http://www.theses.fr/1987LEMA1024.
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Evaluation des differentes grandeurs apparaissant a la transition a partir de considerations de symetrie, et construction de l'hamiltonien de la phase incommensurable. Calcul du dephasage entre premier et second ordre. Analyse des phenomenes de relaxation dans la phase incommensurable. Mise en evidence de deux regimes de fluctuations au voisinage de la temperature de transition t::(1)
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Ait, Yakoub Nouara. "Etude par résonance paramagnétique électronique de la transition de phase normale incommensurable dans ThCl." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376021631.
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Rutzinger, Dieter. "Layered Lanthanide Coinage-Metal Diarsenides: Syntheses, Commensurately and Incommensurately Modulated Structures, Electric and Magnetic Properties." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-26728.
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The crystal structures of the LnAgAs2 and LnAuAs2 compounds were reinvestigated by single-crystal diffraction experiments. Contrary to the respective copper compounds, no stuffed variant of the HfCuSi2 type was found. For CeAuAs2, GdAuAs2 and TbAuAs2, a slight under-occupation of the gold position was determined, the other compounds crystallize in a 1:1:2 ratio. Additionally, LaCuAs2 was synthesized for the first time in a 1:1:2 ratio. Due to the fact that imaging plate diffraction systems were used instead of four-circle diffractometers, satellite reflections could be observed for most of the LnCuAs2 compounds (Ln = Ce, Nd, Sm, Gd, Tb, Ho), CeAuAs2, GdAuAs2 and TbAuAs2. Structure models of GdCuAs2, CeAuAs2, GdAuAs2 and TbAuAs2 were developed, rod and layer groups of the respective structural motives were determined and approximants were presentedDie Kristallstrukturen der LnAgAs2 und LnAuAs2 Verbindungen wurden mittels Einkristallbeugungsexperimenten neu untersucht. Im Gegensatz zu den jeweiligen Kupferverbindungen wurde keine gefüllte Variante des HfCuSi2-Typs gefunden. Im Falle von CeAuAs2, GdAuAs2 und TbAuAs2 wurde eine geringfügige Unterbesetzung der Gold-Position bestimmt, die anderen Verbindungen kristallisieren in einem 1:1:2-Verhältnis. Weiterhin wurde erstmals LaCuAs2 in diesem Verhältnis synthetisiert. Aufgrund der Verwendung von Bildplattensystemen an Stelle von Vierkreisdiffraktometern konnten Satellitenreflexe für den Großteil der LnCuAs2-Verbindungen (Ln = Ce, Nd, Sm, Gd, Tb, Ho), CeAuAs2, GdAuAs2 and TbAuAs2 beobachtet werden. Strukturmodelle von GdCuAs2, CeAuAs2, GdAuAs2 und TbAuAs2 wurden entwickelt, Stab- und Ebenengruppen der einzelnen Strukturmotive wurden bestimmt und Approximanten präsentiert
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Christides, Achille. "Spectrométrie pulsée de R.Q.N. et contribution à l'étude de la phase incommensurable de B-ThBr." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376039655.
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