1,720,987 research outputs found
Ab initio modeling of hydrogen pipe diffusion in palladium
Get PDFA hydrogen economy will require metals for separation, transport and/or storage. Therefore, we need to better understand the behavior of hydrogen in metals. Hydrogen in palladium is a model system, for which there exists an abundance of experimental data. Specifically, quasielastic neutron scattering (QENS) experiments, for the first time, directly measured hydrogen pipe diffusion. The diffusivities and energy barriers from ab initio simulations support these findings, but open questions remain, the most concerning of which pertains to the unusual jump distances reported from fitting the experimental data. Instead of comparing diffusivities and energy barriers from simulation with the parameters extracted from fits to the experimental data, we calculate the spherically-averaged incoherent scattering function to directly compare with experimental data. We find that the experimental fitting procedure introduces errors in the extracted diffusivities and jump distances. We also calculate the intermediate scattering function to compare our simulation results with a wider range of experimental data. From direct comparison of the intermediate scattering function, we find disagreement at small times, which is likely due to the contributions from the vibrational motion of the diffusing hydrogen atom, the host palladium atoms and resonate vibrations. This computational approach allows for validation against experiment, along with a more detailed understanding of the QENS results.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2019-12-01The student, Emily Schiavone, accepted the attached license on 2017-08-21 at 12:31.The student, Emily Schiavone, submitted this Dissertation for approval on 2017-08-21 at 12:46.This Dissertation was approved for publication on 2017-08-21 at 14:50.DSpace SAF Submission Ingestion Package generated from Vireo submission #11608 on 2018-03-13 at 10:32:18Made available in DSpace on 2018-03-13T17:28:59Z (GMT). No. of bitstreams: 3
SCHIAVONE-DISSERTATION-2017.pdf: 4590445 bytes, checksum: bf82413befc190c4ebf5379d7d139aa3 (MD5)
LICENSE.txt: 4212 bytes, checksum: 415f4859916a7abcdb9fddf0c967e9f2 (MD5)
PROQUEST_LICENSE.txt: 4558 bytes, checksum: b8ef3f5750c56ec090b250acf863038c (MD5)
Previous issue date: 2017-08-21Embargo set by: Seth Robbins for item 105423
Lift date: 2020-03-13T17:29:20Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 105423
Lift date: 2020-03-13T17:32:30Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 105423
Lift date: 2020-03-13T17:36:05Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 105423 on 2020-03-14T09:15:25Z
Atomic scale diffusion in complex systems from first principles
Get PDFTransport of point defects controls a variety of materials process such as precipitation, segregation of solutes to grain boundaries and surfaces, and macroscopic properties such as corrosion resistance and ionic conductivity. Therefore, a quantitative prediction of atomic scale transport is crucial to development of new alloys. First principles calculations coupled with advanced diffusion models can accurately predict atomic scale transport mechanisms of point defects in solids. In this work, we examine transport of six solutes - Sn, Cr, Fe, Be, Al and Ni in HCP Zr, and the transport of oxygen vacancies in LaGaO.
Zirconium alloys are used as nuclear fuel cladding materials for light water power reactors and understanding point defect diffusion in Zr will provide a step forward for developing oxidation tolerant alloys. We accurately model the vacancy metastable states observed in HCP Zr and for the first time examine the effect of these states on solute transport. Our results show that Sn and Al diffuse via vacancy mediated mechanism while Cr, Fe, Be and Ni diffuse via the interstitial mechanism at equilibrium. The drag ratios of Cr, Fe, Be and Ni are positive which suggests that non-equilibrium vacancy fluxes could drag these solutes. By combining interstitial and vacancy mediated diffusivities, we demonstrate that supersaturated vacancy concentrations slow down the interstitial diffusion while accelerating the vacancy mediated diffusion.
In recent years, LaGaO has attracted considerable interest for applications in solid oxide fuel due to high oxygen ion mobilities but the atomic scale diffusion mechanism of oxygen vacancies is not well understood. We examine the atomic scale migration of oxygen vacancies in LaGaO and study the effect of strain on the diffusivities. We find that O vacancy diffusion is nearly isotropic in undoped LaGaO and strains up to 2\% can accelerate the diffusivity by two orders of magnitude which could help reduce operating temperatures of the fuel cells. Strong attractive Sr-vacancy and vacancy-vacancy interactions lead to formation of superbasins which trap the vacancy at lower concentrations. However, at sufficiently high concentrations, these superbasins could overlap and lead to fast diffusion via percolation.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-12-01The student, Abhinav Jain, accepted the attached license on 2019-08-14 at 21:02.The student, Abhinav Jain, submitted this Dissertation for approval on 2019-08-14 at 22:04.This Dissertation was approved for publication on 2019-08-19 at 14:03.DSpace SAF Submission Ingestion Package generated from Vireo submission #14424 on 2020-02-28 at 17:20:00Made available in DSpace on 2020-03-02T22:10:20Z (GMT). No. of bitstreams: 4
JAIN-DISSERTATION-2019.pdf: 13438877 bytes, checksum: c1e9186767f578e40febd4e71442e792 (MD5)
Thesis.zip: 18643811 bytes, checksum: 17e93147a74ff976d48f08f4be535d58 (MD5)
LICENSE.txt: 4209 bytes, checksum: 563ea7d222beea77e221f2dfe1d5c82c (MD5)
PROQUEST_LICENSE.txt: 4555 bytes, checksum: 02194063ab0f428e943373f5d552abd4 (MD5)
Previous issue date: 2019-08-19Embargo set by: Seth Robbins for item 113847
Lift date: 2022-03-02T22:10:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113847
Lift date: 2022-03-02T22:11:40Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113847
Lift date: 2022-03-02T22:12:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113847
Lift date: 2022-03-02T22:15:21Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113847
Lift date: 2022-03-02T22:18:25Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 113847 on 2022-03-03T10:15:19Z
Solute transport in magnesium and their uncertainty quantification using density functional theory and green function approach
Get PDFPredictive control of alloy processing requires an accurate knowledge of the thermodynamic and the kinetic information of the system for microstructure simulation. Phenomena such as solute segregation or growth of precipitates occur regularly during alloy processing which involves transport or diffusion of solutes. We investigate interstitial and vacancy-mediated solute transport in the hexagonal close-packed Mg. We utilize density functional theory calculations to determine the energies of interstitials and solute-vacancy configurations, which inform our diffusion model. The diffusion of light elemental solutes B, C, N, and O is investigated by determining their stable interstitial sites and the interpenetrating network formed by these sites. We employ the elastodiffusion tensor to determine the effect of strains on diffusion and find that B, C, and N diffusivity increases with volumetric crystal expansion, while O diffusivity decreases. The vacancy-mediated solute diffusion requires the jump network of vacancy near and away from the solute but the existing diffusion models oversimplify this jump network, severely affecting the accuracy of the transport coefficients. We identify all the symmetry-unique vacancy jumps in the Mg lattice and use our Green function approach to generate the transport database for 61 solutes. Our predictions of solute diffusion coefficients agree well with the available experimental measurements. We also study drag ratios which quantify the drag of solutes by vacancies, and the ring network topologies elucidate their mechanisms. We develop a Bayesian framework to quantify uncertainties in transport coefficients and use it to study uncertainties in transport coefficients due to approximate treatment of electronic exchange and correlation in DFT computed energies.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-08-01The student, Ravi Agarwal, accepted the attached license on 2018-05-15 at 14:43.The student, Ravi Agarwal, submitted this Dissertation for approval on 2018-05-15 at 14:50.This Dissertation was approved for publication on 2018-05-16 at 09:39.DSpace SAF Submission Ingestion Package generated from Vireo submission #12574 on 2018-09-27 at 11:15:41Made available in DSpace on 2018-09-27T16:28:01Z (GMT). No. of bitstreams: 2
AGARWAL-DISSERTATION-2018.pdf: 9908792 bytes, checksum: abc94cd0715a48f696de629ad18ad945 (MD5)
LICENSE.txt: 4209 bytes, checksum: 3e595d019776148c80b8abc296d1a01d (MD5)
Previous issue date: 2018-05-16Embargo set by: Seth Robbins for item 107737
Lift date: 2020-09-27T16:28:07Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107737
Lift date: 2020-09-27T16:30:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107737
Lift date: 2020-09-27T16:31:43Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107737
Lift date: 2020-09-27T16:34:29Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107737 on 2020-09-28T09:15:07Z
Investigation of the mechanical properties and phase stability of Ti-transition metal alloys using first-principle calculations
Get PDFThe ternary Ti-X-B (X=Mo/V/Fe/Nb) alloy system has three distinct material classes depending on the fraction of monoboride phase in the Ti-matrix, which makes them useful for broad applications such as aerospace and biomedical fields. Based on the design principle of searching for Ti-monoboride ceramic phases with higher Young’s modulus, higher Pugh’s ratio, and lower stacking fault energies compared to TiB, we compute the mechanical properties of monoborides with different compositions (X11−xX2x)B using density functional theory. Among all (X10.5X20.5)B, we find that mixed (Ti0.5Mo0.5)B and mixed (Ti0.5V0.5)B as promising candidates for metallic boride compositions for Ti-based alloys and bulk ceramics. Among these two ternary mixed monoborides, we focus on β-stabilizer Mo and study toughness of BCC phase Ti-Mo alloys to understand the effect of solutes on the plastic deformation. We calculate elastic constants, stacking fault energies and dislocation core geometries of non-dilute BCC Ti-Mo random alloys. Studies of dislocation core structures have relied on a variety of coupling techniques to manage the far-field strain fields; one very successful approach for pure materials has been the flexible boundary condition (FBC) method based on the lattice Green function. However, applying FBC to compute the dislocation core structures in systems with multiple components adds more complexity due to the initial atomic forces in the far-field where the atomic positions are not updated within the FBC framework. We describe a methodology to compute the screw dislocation core geometry of non-dilute BCC TiMo random alloy efficiently by combining first-principles calculations with an optimized Ti-Mo Gaussian Approximation Potential (GAP) specifically designed for use with flexible boundary conditions. We illustrate our algorithm to determine the sizes of LGF buffer and relaxation buffer in dislocation geometry using our Ti-Mo GAP model. We also use the GAP model for relaxation of the initial dislocation geometry and computing the force constants for the dislocation of BCC Ti0.5Mo0.5 random alloy to construct the lattice Green function. The relaxed dislocation screw core structure of the BCC Ti-Mo random alloy are discussed. Finally, we demonstrate the DFT database to build our Ti-Mo GAP model and show the validation and predictions for energy, force, elastic constant, and force constants of Ti-Mo alloys.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-12-01The student, Hyojung Kim, accepted the attached license on 2019-08-15 at 22:03.The student, Hyojung Kim, submitted this Dissertation for approval on 2019-08-15 at 22:20.This Dissertation was approved for publication on 2019-08-16 at 14:39.DSpace SAF Submission Ingestion Package generated from Vireo submission #14426 on 2020-02-28 at 17:20:05Made available in DSpace on 2020-03-02T22:10:20Z (GMT). No. of bitstreams: 2
KIM-DISSERTATION-2019.pdf: 15930406 bytes, checksum: 612c4c23cd8aa254038cba58fc1b5680 (MD5)
LICENSE.txt: 4208 bytes, checksum: b94c401504a2f558924af0ef64abe99d (MD5)
Previous issue date: 2019-08-16Embargo set by: Seth Robbins for item 113848
Lift date: 2022-03-02T22:10:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113848
Lift date: 2022-03-02T22:11:40Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113848
Lift date: 2022-03-02T22:12:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113848
Lift date: 2022-03-02T22:15:21Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113848
Lift date: 2022-03-02T22:18:25Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 113848 on 2022-03-03T10:15:25Z
Database optimization algorithm for empirical potentials
Get PDFThe development for accurate and efficient empirical potential models requires years of efforts and is highly intuitional. This study provides an automated, quantitative algorithm to find the optimal empirical potential model for a pre-determined testing set of desired structure properties. We employ Bayesian sampling technique to estimate the errors for the structural property functions in the testing set. We provide the first analytical derivations of how modifications in the fitting database affect the testing set errors. A new binary modified embedded-atom method functional form is developed for Ti-O interactions where O is in the dilute limit. The optimal Ti-O potential are tested against a variety of structure properties to verify the transferability of the potential. We propose and optimize two types of objective functions which measures the transferability in the testing set. One aims to minimize the relative errors of different fitting databases for the testing set, and the other uses the logistic function in classification regression analysis to categorize the prediction errors in the testing set into good and bad ones. We develop a parallelized genetic algorithm to efficiently evaluate the objective function and perform global search for the optimal empirical potential model.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-05-01The student, Pinchao Zhang, accepted the attached license on 2016-02-29 at 19:44.The student, Pinchao Zhang, submitted this Dissertation for approval on 2016-02-29 at 19:47.This Dissertation was approved for publication on 2016-03-01 at 13:19.DSpace SAF Submission Ingestion Package generated from Vireo submission #9048 on 2016-07-07 at 13:48:10Made available in DSpace on 2016-07-07T20:26:45Z (GMT). No. of bitstreams: 3
ZHANG-DISSERTATION-2016.pdf: 8672930 bytes, checksum: f606583c286acd49a335b50bcdd1689c (MD5)
LICENSE.txt: 4210 bytes, checksum: f792fabdaec75c00c7113b40c07b7321 (MD5)
PROQUEST_LICENSE.txt: 4556 bytes, checksum: e4b8302d27802bf5d5c2f2e2f8e93057 (MD5)
Previous issue date: 2016-03-01Embargo set by: Seth Robbins for item 93066
Lift date: 2018-07-07T20:28:14Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 93066
Lift date: 2018-07-07T20:35:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 93066 on 2018-07-08T09:15:36Z
Proton-coupled electron transfer reactions in bio-inspired catalysis
Get PDFNature often serves as a seminal source of inspiration for the design of catalysts, which is likely due to the efficiency of many biological systems. Bio-inspired design is especially applicable in many energy conversion processes, such as artificial photosynthesis, and in the development of alternative renewable energy technologies. Often proton-coupled electron transfer (PCET) is central to the interconversion of energy. Consequently, understanding the role of PCET in the mechanisms of bio-inspired catalysts can aid in the design of next generation catalysts and the elucidation of guiding design principles. In nature, hydrogenases are the most active catalysts for hydrogen production, with rates and overpotentials comparable to leading, synthetic Pt catalysts while utilizing earth abundant metal centers in their active sites. Density functional theory calculations, in conjunction with complementary experiments, were conducted to understand the underlying physical principles of hydrogenase-based models. Our collective studies on hydrogenase-based models have revealed two emerging themes: (1) one metal center is acid-base active while the adjacent metal center is redox active, and (2) the importance of considering thermodynamically less stable but active intermediates.
Nature also often relies on mediators to couple electrons and protons between various cycles in catalysis. A prime example of the importance of electron-proton transfer mediators is photosynthesis, where the slow water splitting reaction and the fast photoinitation of a reaction center are mediated by a Tyr-His redox pair in Photosystem II. Understanding the fundamental PCET processes in Tyr-His models is helpful for the design of photoelectrochemical water splitting cells, where water oxidation provides protons and electrons for hydrogen production via a hydrogen-evolving catalyst, such as those based on hydrogenases. To understand the kinetics of this reaction, a nonadiabatic PCET rate theory is applied to predict and interpret kinetic isotope effects for Tyr-His model systems. Importantly, theory predicted new mediators capable of two proton transfers coupled to an electron transfer, and these predictions were later validated experimentally. In addition to the Tyr-His redox mediator, Photosystem II also employs a quinone derivative to mediate the transfer of electrons and protons across the membrane. This plastoquinone cycles between the oxidized quinone state and the doubly-reduced, doubly-protonated hydroquinone state (i.e., a 2 e–/2 H+ PCET process). Our analysis of fundamental redox behaviors of over one hundred quinones using linear scaling relationships, such as Hammett correlations, revealed linear correlations between 1 e– reduction potentials, pKa values, and 2 e–/2 H+ reduction potentials with an effective Hammett constant. More importantly, key deviations resulting from hydrogen-bonding, halogenated, charged, and sterically-bulky substituents were identified and analyzed. In principle, these types of deviations can be leveraged to further develop and tune quinone-based catalysts, mediators, or devices beyond the redox properties predicted by standard linear scaling relationships.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2017-09-29 without embargo termsThe student, Mioy Huynh, accepted the attached license on 2017-07-13 at 13:41.The student, Mioy Huynh, submitted this Dissertation for approval on 2017-07-13 at 13:47.This Dissertation was approved for publication on 2017-07-13 at 17:44.DSpace SAF Submission Ingestion Package generated from Vireo submission #11455 on 2017-09-29 at 11:30:11Made available in DSpace on 2017-09-29T17:56:50Z (GMT). No. of bitstreams: 2
HUYNH-DISSERTATION-2017.pdf: 43000621 bytes, checksum: 0e63a5cd3dddb5e19a9e85f2e4fc42f6 (MD5)
LICENSE.txt: 4207 bytes, checksum: 096e40a1a475739bd4b5e1619e88ccb7 (MD5)
Previous issue date: 2017-07-1
"“Phonon"" and electron transport in glass-crystal dual materials"
Get PDFDisorder has been a long-standing driver across all sectors of materials engineering, ranging from energy and transportation, to electronics and communications, and to biomedicine and environment. Disorder engineering has focused primarily on tuning its spatial configuration and distribution to establish desirable structure-property relations. However, while band theory and phenomenological random-walk models are available in the crystalline and amorphous limits respectively, the picture for energy and charge transport in hybrid ordered-disordered materials is still incomplete. This is especially true when structural disorder possesses long-range correlation and dynamic nature. These subjects are the concern of this work. The goal is to numerically understand how different types of disorder can modify phonon and electron transport properties.
I first establish how uncorrelated structural disorder affects vibrational energy transport in low-dimensional disordered materials. The recently synthesized amorphous graphene and glassy diamond nanothreads are studied. Modal localization analysis, molecular dynamics simulations, and a generalized analytical model together demonstrate that the thermal properties of these materials exhibit both similarities and differences from disordered 3D materials. Similar to 3D, the low-dimensional systems exhibit both propagating and diffusive vibrational modes. Different from 3D, however, diffusonic contribution to thermal transport in these low-dimensional systems is shown to be negligible, which results from the intrinsically different nature of random walks in lower dimensions. Despite the lack of diffusons, the suppression of thermal conductivity due to disorder in low-dimensional systems is shown to be mild. The mild suppression originates from the presence of low-frequency vibrational modes that maintain well-defined polarizations and help preserve the thermal conductivity in the presence of disorder. This study brings the domains of low-dimensional materials and disordered materials together, and establishes appropriate theoretical approaches to characterize the vibrational energy transport at the atomic scale when disorder is present.
The second part deals with correlated but static disorder. The model system will be a hybrid ordered/disordered nanocomposite that consists of a crystalline silicon membrane decorated by regularly patterned disordered regions. Combining molecular dynamics and the Boltzmann theory, I predict a thermoelectric figure of merit ZT ≈ 0.5 at room temperature. To facilitate the Boltzmann theory, I have derived an analytical model for electron scattering with cylindrical defective regions based on partial-wave analysis. Furthermore, I find glass-crystal duality for the vibrational transport in these hybrid systems. Lattice dynamics reveals substantial hybridization between the localized and delocalized modes, which induces avoided crossings and harmonic broadening in the dispersion. Allen/Feldman theory shows that the hybridization and avoided crossings are the dominant mechanisms of the reduction. Anharmonic scattering is also enhanced in the patterned nanocomposites, further contributing to the reduction. These findings indicate that “patterned disorder” can be a viable strategy to tailor vibrational transport, and ion beam irradiation could be a promising fabrication strategy.
In the third part, I focus on the disorder that is both correlated and dynamic. Two lead iodide perovskites, XPbI3 (X=Cs, methylammonium), are the representative materials. In these perovskites, sublattice symmetrybreaking and dynamically correlated disorder affect substantially their vibrational and thermal properties. In contrast to the conventional phononic theory, analysis of spectral energy density reveals that thermal carriers exhibit more propagonic and diffusonic characteristics. Strong anharmoncity in these perovskites, two orders higher than silicon, is observed both on the inorganic framework and surprisingly for the interactions between PbI6 framework modes and localized A-site modes. Based on first-principles calculations, I ascribe the former to long-range interactions arising from resonant bonding, while the latter to A-site rattling in CsPbI3, and polar rotor scattering instead in MAPbI3. I also observe “waterfall-like” dispersions, which I show to be an emergent phenomenon due to dynamical averaging of different dispersions that belong to energetically equivalent disordered phases. This work would be of interest to the design and functionalization of a broad family of hybrid materials, including metal-organic frameworks, molecular crystals and hierarchically organized materials.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2019-02-05 without embargo termsThe student, Taishan Zhu, accepted the attached license on 2018-08-30 at 10:58.The student, Taishan Zhu, submitted this Dissertation for approval on 2018-08-30 at 11:15.This Dissertation was approved for publication on 2018-08-30 at 13:43.DSpace SAF Submission Ingestion Package generated from Vireo submission #12987 on 2019-02-05 at 11:07:44Made available in DSpace on 2019-02-06T19:32:39Z (GMT). No. of bitstreams: 3
ZHU-DISSERTATION-2018.pdf: 12097117 bytes, checksum: 6748692a73ad85823d59fe30d964955a (MD5)
LICENSE.txt: 4208 bytes, checksum: 63a5c069662f9886aef4ec3ff5b5880f (MD5)
PROQUEST_LICENSE.txt: 4554 bytes, checksum: f237243923d28f8b0ddfd2ea681560da (MD5)
Previous issue date: 2018-08-3
Multi-scale investigation of vacancy-mediated diffusion of Si in Ni near an edge dislocation
Get PDFDuring the last decade, studies have focused the development of creep-resistant alloys that can tolerate the high temperatures and high irradiation doses within nuclear reactors. One important mechanism of irradiation creep is the migration of dislocations, which arises as a direct consequence of point-defect diffusion near dislocations and is also affected by the presence of solutes. In this work, we develop a multi-scale model which is able to simulate the diffusion of point-defects and solute atoms in the dislocation strain field. We first use kinetic Monte Carlo simulations to investigate the strain effects on the transport coefficients for vacancies and Si in FCC Ni. We then use a mesoscale model, which takes the strain-dependent transport coefficient computed by self-consistent mean field calculations, to model the irradiation induced solute segregation around an edge dislocation in FCC Ni-Si alloy. At last, we extend the mesoscale model into an multi-scale approach by coupling it to a discrete model which captures the thermally activated atomic transitions and reactions in the dislocation core. We use the multi-scale approach to investigate the climb motion of an edge dislocation in FCC Ni-Si alloy, induced by irradiation and by an externally applied stress. We also quantify the effect of solute on the climb velocity.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-12-01The student, Zebo Li, accepted the attached license on 2017-09-05 at 15:03.The student, Zebo Li, submitted this Dissertation for approval on 2017-09-05 at 15:13.This Dissertation was approved for publication on 2017-09-06 at 15:32.DSpace SAF Submission Ingestion Package generated from Vireo submission #11634 on 2018-03-13 at 09:54:54Made available in DSpace on 2018-03-13T15:20:58Z (GMT). No. of bitstreams: 2
LI-DISSERTATION-2017.pdf: 16323645 bytes, checksum: 96db40128fed400cf5818bd6724deccf (MD5)
LICENSE.txt: 4204 bytes, checksum: c85f02dd2445690b49525140727b01b3 (MD5)
Previous issue date: 2017-09-06Embargo set by: Seth Robbins for item 105137
Lift date: 2020-03-13T15:21:19Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 105137
Lift date: 2020-03-13T15:25:40Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 105137
Lift date: 2020-03-13T15:28:52Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 105137 on 2020-03-14T09:15:19Z
Computation and application of the lattice Green function to dislocations in metals, intermetallics, and semiconductors
Get PDFDislocations are fundamental crystallographic defects that play key roles in determining material properties. The first step to understanding dislocations and being able to model them accurately is knowing their geometry. While the far-field geometry of a dislocation can be well described by anisotropic continuum elasticity theory, the elastic solution diverges close to the dislocation core. Methods such as density functional theory (DFT) are needed to accurately determine the geometry in the dislocation core; however, the long-range strain field of a dislocation is incompatible with periodic boundary conditions, making it challenging to perform DFT calculations of isolated dislocations. The flexible boundary condition (FBC) approach captures the correct long-range response of the dislocation by coupling the dislocation core to an infinite harmonic bulk through the lattice Green function (LGF). To improve the accuracy and efficiency of the FBC approach, we develop a numerical method to compute the LGF specifically for a dislocation geometry by directly accounting for its topology. This is in contrast to previous methods, where the LGF was computed for the perfect bulk as an approximation for the dislocation. The dislocation LGF computed using our method describes the response around the dislocation more accurately than the perfect bulk LGF, and relaxes dislocation core geometries efficiently when used within the FBC approach. We apply this method to compute the LGF for screw, edge, and mixed dislocations in metals, intermetallics, and semiconductors, and use them within the FBC approach coupled with DFT to accurately determine the equilibrium dislocation core structures. First, we compute the core structures of five different dislocations in BCC iron -- screw, mixed, edge, edge, and edge dislocations, and find a dependence of the local magnetic moment on the local strain. Next, we compute the relaxed core structures of the Ni screw dislocation and the \NiAl\ superdislocation, demonstrating the first fully atomistic DFT calculation of an extended dislocation core structure in an intermetallic. Finally, we compute single-period, double-period, and quadruple-period dislocation core reconstructions of the 60 Cd-core dislocation in CdTe. Through this work, we demonstrate the generality and versatility of our method to compute LGF and relax dislocation core structures in a wide range of technologically important material systems.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-08-01The student, Anne Marie Tan, accepted the attached license on 2018-05-25 at 14:03.The student, Anne Marie Tan, submitted this Dissertation for approval on 2018-05-25 at 14:11.This Dissertation was approved for publication on 2018-05-25 at 15:57.DSpace SAF Submission Ingestion Package generated from Vireo submission #12595 on 2018-09-27 at 11:15:49Made available in DSpace on 2018-09-27T16:28:03Z (GMT). No. of bitstreams: 2
TAN-DISSERTATION-2018.pdf: 14728666 bytes, checksum: 9db8bdc0f6deb7c0a4d8d6462c5a651b (MD5)
LICENSE.txt: 4211 bytes, checksum: 105c1e627cfc26dffefde13d6ee5ed8b (MD5)
Previous issue date: 2018-05-25Embargo set by: Seth Robbins for item 107743
Lift date: 2020-09-27T16:28:07Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107743
Lift date: 2020-09-27T16:30:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107743
Lift date: 2020-09-27T16:31:43Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107743
Lift date: 2020-09-27T16:34:29Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107743 on 2020-09-28T09:15:13Z
- …
