1,246 research outputs found

    Ab Initio Study of Phase Stability in Doped TiO2

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    Ab-initio density functional theory (DFT) calculations of the relative stability of anatase and rutile polymorphs of TiO2 were carried using all-electron atomic orbitals methods with local density approximation (LDA). The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F- doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F>Si>Fe>Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies

    Magnetic Properties of Hydrogenated TiFe0.9Co0.1

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    The thermodynamic properties of the TiFe0.9Co0.1?H system and its magnetic properties with various hydrogen contents were examined. The pressure-composition isotherm curves showed a plateau region, and the change in the enthalpy with monohydride formation was similar to that of TiFe. From the conventional magnetic properties examinations, TiFe0.9Co0.1 was found to show no magnetic transition down to 10 K. The magnetic susceptibility of TiFe0.9Co0.1 increased with hydrogen uptake, but no ferromagnetic behavior was observed up to the hydrogen content of TiFe0.9Co0.1H0.6 at room temperature. The change in magnetic susceptibility with hydrogen uptake could be explained qualitatively by the band structure calculatio

    Topological insulators and thermoelectric materials

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    Topological insulators (TIs) are a new quantum state of matter which have gapless surface states inside the bulk energy gap. Starting with the discovery of two dimensional TIs, the HgTe-based quantum wells, many new topological materials have been theoretically predicted and experimentally observed. Currently known TI materials can possibly be classified into two families, the HgTe family and the Bi2Se family. The signatures found in the electronic structure of a TI also cause these materials to be excellent thermoelectric materials. On the other hand, excellent thermoelectric materials can be also topologically trivial. Here we present a short introduction to topological insulators and thermoelectrics, and give examples of compound classes were both good thermoelectric properties and topological insulators can be found.Comment: Phys. Status Solidi RRL, accepte

    Doctor of Philosophy

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    dissertationThe optical spectrum of diatomic OsC has been investigated by means of resonant two-photon ionization spectroscopy. Spectra for six OsC isotopomers, 192Os12C (40.3 % natural abundance), 190Os12C (26.0 %), 189Os12C (16.0 %), 188Os12C (13.1%), 187Os12C (1.9 %), and 186Os12C (1.6 %), were recorded and rotationally analyzed. The ground state was found to be X 3Δ3, deriving from the 1δ3 3σ1 electronic configuration. Four bands were found to originate from the X 3Δ3 ground state, giving B0"=0.533 492(33) cm-1 and r0O=1.672 67(5) Å for the 192Os12C isotopomer (1σ error limits). The optical spectrum of diatomic TaC has been investigated, with transitions recorded in the range from 17 850 to 20 000 cm-1. Seven bands were rotationally resolved and analyzed to obtain ground and excited state parameters, including band origins, upper and lower state rotational constants and bond lengths, Fermi contact parameter, bF, for the ground state, and lambda doubling parameters for the excited states. The ground state of TaC was found to be X2Σ+, originating from the 1σ2 2σ2 1π4 3σ1 electronic configuration, giving B0"=0.489683(83) cm-1, r0"=1.74901(15) Å, and bF"=0.13120(36) cm-1 (1σ error limits), for 181Ta12C. Diatomic ZrFe and TiFe have been spectroscopically investigated for the first time. Band origins, excited state vibrational frequencies and anharmonicities, excited state lifetimes, the ground state vibrational interval, ΔG"1/2, rotational constants and Ω values, bond lengths and rotation-vibration constants are reported for the five most abundant isotopomers of ZrFe and seven most abundant isotopomers of TiFe. The ground states of ZrFe and TiFe are assigned as nominally sextuply-bonded 1Σ+ (Ω = 0+) states deriving from the 1σ21π42σ21δ4 electronic configurations

    In-situ neutron diffraction during reversible deuterium loading in Ti-rich and Mn-substituted Ti(Fe,Mn)0.90 alloys

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    Hydrogen is an efficient energy carrier that can be produced from renewable sources, enabling the transition towards CO2-free energy. Hydrogen can be stored for a long period in the solid-state, with suitable alloys. Ti-rich TiFe0.90 compound exhibits a mild activation process for the first hydrogenation, and Ti (Fe,Mn)0.90 substituted alloys can lead to the fine tuning of equilibrium pressure as a function of the final application. In this study, the crystal structure of TiFe(0.90-x)Mnx alloys (x = 0, 0.05 and 0.10) and their deuterides has been determined by in-situ neutron diffraction, while recording Pressure-Composition Isotherms at room temperature. The investigation aims at analysing the influence of Mn for Fe substitution in Ti-rich Ti(Fe,Mn)0.90 alloys on structural properties during reversible deuterium loading, which is still unsolved and seldom explored. After activation, samples have been transferred into custom-made stainlesssteel and aluminium alloy cells used for in-situ neutron diffraction experiments during deuterium loading at ILL and ISIS neutron facilities, respectively. The study enables remarkable understanding on hydrogen storage, basic structural knowledge, and support to the industrial application of TiFe-type alloys for integrated hydrogen tank in energy storage systems by determining the volume expansion during deuteration. Furthermore, the study demonstrates that different contents of Mn do not significantly change the volumetric expansion during phase transitions, affecting only the deuterium content for the gamma phase and the cell evolution for the beta phase. The study confirms that the deuterated structures of the gamma phase upon absorption, beta and ' phase upon desorption, correspond to S.G. Cmmm, P2221 and Pm-3m, respectively.(c) 2022 Elsevier B.V. All rights reserved

    Influence of Interstitial Impurities (H, B, C) on Grain Boundary Cohesion in B2 Ti-based Alloys

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    The investigation of hydrogen, boron and carbon sorption properties at the Σ5(310) symmetrical tilt grain boundary (GB) and (310) free surface (FS) in B2 Ti-based alloys was carried out by the plane-wave pseudopotential method within density functional theory. The most preferential positions for interstitial impurities at GB were determined. It was shown that impurities sorption energies at GB depend strongly on their local environment. The analysis of electronic properties allows us to establish the microscopic na-ture of chemical bonding of all considered impurities at GB. It was shown that H decreases more signifi-cantly the surface energies than the GB energy in contrast to B and C. This results in decreasing the Grif-fith work that indicates also the decrease of the strength of grain boundary. The segregation of H at the GB makes intergranular fracture much easier because the bonding between metal atoms, which are neigh-bors of H, is weakened. The segregation behavior of hydrogen confirms it as an embrittler for B2 Ti-based alloys. At the same time boron and carbon segregation contrast to hydrogen increase the GB cohesion. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3551

    Advanced CO2 removal process control and monitor instrumentation development

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    A progam to evaluate, design and demonstrate major advances in control and monitor instrumentation was undertaken. A carbon dioxide removal process, one whose maturity level makes it a prime candidate for early flight demonstration was investigated. The instrumentation design incorporates features which are compatible with anticipated flight requirements. Current electronics technology and projected advances are included. In addition, the program established commonality of components for all advanced life support subsystems. It was concluded from the studies and design activities conducted under this program that the next generation of instrumentation will be greatly smaller than the prior one. Not only physical size but weight, power and heat rejection requirements were reduced in the range of 80 to 85% from the former level of research and development instrumentation. Using a microprocessor based computer, a standard computer bus structure and nonvolatile memory, improved fabrication techniques and aerospace packaging this instrumentation will greatly enhance overall reliability and total system availability
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