{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/109514"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/109514","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Novel phase and phase transition behavior of a superionic conductor observed on the nanoscale","abstract":"This dissertation documents the work performed in the pursuit of a PhD degree in the research group of Prof. Prashant K. Jain at the University of Illinois at Urbana-Champaign. I employed in-situ transmission electron microscopy (TEM) for understanding the ionic structure, vacancy ordering, phase transitions, and ion transport in a prototypical fast-ion conductor, copper selenide. Major objectives of my work were to elucidate i) the nature of the structural phase transition by which copper selenide becomes a superionic phase and ii) the microscopic mechanisms of ionic motion in this material. My studies were performed on nanostructures of copper selenide. Chapter 1 introduces the concept of a superionic conductor and describes one particular example, copper selenide, which is the model system studied in my work. Also, I briefly discuss in-situ high-resolution TEM the primary technique I used, and the advantages and capabilities this method offered for my studies of copper selenide. Chapter 2 presents an interesting finding made in the course of my TEM studies: the observation of a novel phase of cuprous selenide in nanocrystals. This novel phase exhibits an unusually longer-range of Cu-vacancy ordering and is found from density functional theory (DFT) calculations to be a metastable phase. After thorough characterization of the different phases of copper selenide in nanocrystals under TEM, I investigated, using in-situ TEM, the phase transition behavior of copper selenide nanocrystals from their ordered state to their superionic phase, the results of which are described in Chapter 3. From the spatiotemporal kinetics interrogated by in-situ TEM, we determined the precise nucleation sites of the phase transition and establish a correlation between the dynamics of the cations and anions in the transition. Next, we studied using in-situ TEM the ionic structure and dynamics in copper selenide nanowires, which are one-dimensional structures with anisotropy unlike zero-dimensional nanocrystals. As described in Chapter 4, I observed anti-phase boundaries, a type of planar defect, in the nanowires. Investigation of the phase transition behavior near anti-phase boundaries led us to conclude that this planar defect impedes the growth of the superionic phase. Also, I observed the motion of this defect under electron beam irradiation. From the characteristics of the motion, we infer how copper ions migrate in the copper selenide lattice. Taken together, my work leveraged well-defined nanostructures and in-situ TEM to shed broadly applicable insights into the atomistic dynamics involved in a phase transition, vacancies and defects in ionic compounds, and the nature of cation transport in superionic materials.","abstract_html":"This dissertation documents the work performed in the pursuit of a PhD degree in the research group of Prof. Prashant K. Jain at the University of Illinois at Urbana-Champaign. I employed in-situ transmission electron microscopy (TEM) for understanding the ionic structure, vacancy ordering, phase transitions, and ion transport in a prototypical fast-ion conductor, copper selenide. Major objectives of my work were to elucidate i) the nature of the structural phase transition by which copper selenide becomes a superionic phase and ii) the microscopic mechanisms of ionic motion in this material. My studies were performed on nanostructures of copper selenide. Chapter 1 introduces the concept of a superionic conductor and describes one particular example, copper selenide, which is the model system studied in my work. Also, I briefly discuss in-situ high-resolution TEM the primary technique I used, and the advantages and capabilities this method offered for my studies of copper selenide. Chapter 2 presents an interesting finding made in the course of my TEM studies: the observation of a novel phase of cuprous selenide in nanocrystals. This novel phase exhibits an unusually longer-range of Cu-vacancy ordering and is found from density functional theory (DFT) calculations to be a metastable phase. After thorough characterization of the different phases of copper selenide in nanocrystals under TEM, I investigated, using in-situ TEM, the phase transition behavior of copper selenide nanocrystals from their ordered state to their superionic phase, the results of which are described in Chapter 3. From the spatiotemporal kinetics interrogated by in-situ TEM, we determined the precise nucleation sites of the phase transition and establish a correlation between the dynamics of the cations and anions in the transition. Next, we studied using in-situ TEM the ionic structure and dynamics in copper selenide nanowires, which are one-dimensional structures with anisotropy unlike zero-dimensional nanocrystals. As described in Chapter 4, I observed anti-phase boundaries, a type of planar defect, in the nanowires. Investigation of the phase transition behavior near anti-phase boundaries led us to conclude that this planar defect impedes the growth of the superionic phase. Also, I observed the motion of this defect under electron beam irradiation. From the characteristics of the motion, we infer how copper ions migrate in the copper selenide lattice. Taken together, my work leveraged well-defined nanostructures and in-situ TEM to shed broadly applicable insights into the atomistic dynamics involved in a phase transition, vacancies and defects in ionic compounds, and the nature of cation transport in superionic materials.","abstract_has_math":false,"creators":["Heo, Jaeyoung"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Materials Science & Engr","degree_department":null,"school":null,"contributors":["Jain, Prashant K","Zuo, Jian-Min","Shim, Moonsub","Chen, Qian"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2021,"date_issued":"2021-03-05T21:42:45Z","date_published":"2021-03-05T21:42:45Z","updated_at":"2026-07-22T22:24:50Z","subjects":["Chemical structure","Defects in solids","Transmission electron microscopy","fast-ion transport","nanostructure"],"languages":["en"],"rights":["Copyright 2020 Jaeyoung Heo"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/109514","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Jain, Prashant K","Zuo, Jian-Min","Shim, Moonsub","Chen, Qian"]},{"key":"dc:creator","label":"Author","values":["Heo, Jaeyoung"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2021-03-05T21:42:45Z","2023-03-05T21:43:00Z","2020-12-03","2020-12"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science & Engr"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Chemical structure","Defects in solids","Transmission electron microscopy","fast-ion transport","nanostructure"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2020 Jaeyoung Heo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/109514"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["This dissertation documents the work performed in the pursuit of a PhD degree in the research group of Prof. Prashant K. Jain at the University of Illinois at Urbana-Champaign. I employed in-situ transmission electron microscopy (TEM) for understanding the ionic structure, vacancy ordering, phase transitions, and ion transport in a prototypical fast-ion conductor, copper selenide. Major objectives of my work were to elucidate i) the nature of the structural phase transition by which copper selenide becomes a superionic phase and ii) the microscopic mechanisms of ionic motion in this material. My studies were performed on nanostructures of copper selenide. Chapter 1 introduces the concept of a superionic conductor and describes one particular example, copper selenide, which is the model system studied in my work. Also, I briefly discuss in-situ high-resolution TEM the primary technique I used, and the advantages and capabilities this method offered for my studies of copper selenide. Chapter 2 presents an interesting finding made in the course of my TEM studies: the observation of a novel phase of cuprous selenide in nanocrystals. This novel phase exhibits an unusually longer-range of Cu-vacancy ordering and is found from density functional theory (DFT) calculations to be a metastable phase. After thorough characterization of the different phases of copper selenide in nanocrystals under TEM, I investigated, using in-situ TEM, the phase transition behavior of copper selenide nanocrystals from their ordered state to their superionic phase, the results of which are described in Chapter 3. From the spatiotemporal kinetics interrogated by in-situ TEM, we determined the precise nucleation sites of the phase transition and establish a correlation between the dynamics of the cations and anions in the transition. Next, we studied using in-situ TEM the ionic structure and dynamics in copper selenide nanowires, which are one-dimensional structures with anisotropy unlike zero-dimensional nanocrystals. As described in Chapter 4, I observed anti-phase boundaries, a type of planar defect, in the nanowires. Investigation of the phase transition behavior near anti-phase boundaries led us to conclude that this planar defect impedes the growth of the superionic phase. Also, I observed the motion of this defect under electron beam irradiation. From the characteristics of the motion, we infer how copper ions migrate in the copper selenide lattice. Taken together, my work leveraged well-defined nanostructures and in-situ TEM to shed broadly applicable insights into the atomistic dynamics involved in a phase transition, vacancies and defects in ionic compounds, and the nature of cation transport in superionic materials.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-12-01","The student, Jaeyoung Heo, accepted the attached license on 2020-11-30 at 18:02.","The student, Jaeyoung Heo, submitted this Dissertation for approval on 2020-11-30 at 21:46.","This Dissertation was approved for publication on 2020-12-03 at 08:07.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15999 on 2021-03-04 at 16:20:01","Made available in DSpace on 2021-03-05T21:42:45Z (GMT). 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Jain at the University of Illinois at Urbana-Champaign. I employed in-situ transmission electron microscopy (TEM) for understanding the ionic structure, vacancy ordering, phase transitions, and ion transport in a prototypical fast-ion conductor, copper selenide. Major objectives of my work were to elucidate i) the nature of the structural phase transition by which copper selenide becomes a superionic phase and ii) the microscopic mechanisms of ionic motion in this material. My studies were performed on nanostructures of copper selenide. Chapter 1 introduces the concept of a superionic conductor and describes one particular example, copper selenide, which is the model system studied in my work. Also, I briefly discuss in-situ high-resolution TEM the primary technique I used, and the advantages and capabilities this method offered for my studies of copper selenide. Chapter 2 presents an interesting finding made in the course of my TEM studies: the observation of a novel phase of cuprous selenide in nanocrystals. This novel phase exhibits an unusually longer-range of Cu-vacancy ordering and is found from density functional theory (DFT) calculations to be a metastable phase. After thorough characterization of the different phases of copper selenide in nanocrystals under TEM, I investigated, using in-situ TEM, the phase transition behavior of copper selenide nanocrystals from their ordered state to their superionic phase, the results of which are described in Chapter 3. From the spatiotemporal kinetics interrogated by in-situ TEM, we determined the precise nucleation sites of the phase transition and establish a correlation between the dynamics of the cations and anions in the transition. Next, we studied using in-situ TEM the ionic structure and dynamics in copper selenide nanowires, which are one-dimensional structures with anisotropy unlike zero-dimensional nanocrystals. As described in Chapter 4, I observed anti-phase boundaries, a type of planar defect, in the nanowires. Investigation of the phase transition behavior near anti-phase boundaries led us to conclude that this planar defect impedes the growth of the superionic phase. Also, I observed the motion of this defect under electron beam irradiation. From the characteristics of the motion, we infer how copper ions migrate in the copper selenide lattice. Taken together, my work leveraged well-defined nanostructures and in-situ TEM to shed broadly applicable insights into the atomistic dynamics involved in a phase transition, vacancies and defects in ionic compounds, and the nature of cation transport in superionic materials.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-12-01","The student, Jaeyoung Heo, accepted the attached license on 2020-11-30 at 18:02.","The student, Jaeyoung Heo, submitted this Dissertation for approval on 2020-11-30 at 21:46.","This Dissertation was approved for publication on 2020-12-03 at 08:07.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15999 on 2021-03-04 at 16:20:01","Made available in DSpace on 2021-03-05T21:42:45Z (GMT). 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