{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/50388"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/50388","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"New modalities for strain engineering of lead-free perovskite ferroelectric thin films","abstract":"Over the last few decades, considerable attention has been given to the development of lead-based ferroelectric systems such as PbZr1-xTixO3 due to their robust high temperature ferroelectric properties, as well as the presence of the so-called morphotropic phase boundary (MPB) ̶ a temperature-independent composition-driven structural instability that results in superior dielectric and piezoelectric properties. However, increasing environmental concerns are driving efforts towards the development of lead-free ferroelectrics such as BiFeO3, BaTiO3, and others. Previous work on epitaxial BiFeO3 thin films have shown that large compressive strains can drive the formation of complex mixed-phase structures with enhanced electromechanical responses (4-5% strains). In this work, we probe the nanoscale distribution of phases present in these mixed-phase structures using a combination of epitaxial thin-film growth and characterization techniques such as x-ray diffraction and piezoresponse force microscopy. We show, for the first time, the presence of monoclinic distortions and intermediate phases (akin to conventional MPB systems) in the mixed-phase films that are crucial for enhanced electromechanical responses. We then present thickness- and temperature- dependent phase-evolution studies that indicate the presence of a strain-spinodal between the various structural polymorphs of BiFeO3 to be the origin of mixed-phase formation. Finally, we discuss limitations due to a breakdown in epitaxy that occurs in thicker films and present chemical alloying-based approaches to mitigate these challenges. Having highlighted strain relaxation with increasing film thickness as a fundamental limitation to epitaxial-strain control, we explore an alternative route involving the use of a combination of defect-engineering and epitaxial strain to stabilize enhanced deformation states in materials. For this, we present a systematic study of BaTiO3 thin films, and show that epitaxial strain can be used to control the ordering of growth-induced defects driving deterministic additional out-of-plane strains that can enhance the ferroelectric Curie temperature to values exceeding 800°C without any need to change substrates. Such a combined control of epitaxial strain and engineered defect-structures provides a new pathway to extend the limits of strain-control of materials and properties. Lastly, we investigate a new route involving the use of epitaxial strain in conjunction with controlled composition- and strain- gradients to tune the thermal stability of dielectric responses of ferroelectric thin films. We present preliminary studies that reveal enhanced relative dielectric permittivity values of ~750, that change by less than 10% over a wide temperature range from 25-350ºC in compositionally-graded epitaxial BaxSr1-xTiO3 thin films, which is promising for next-generation microwave applications.","abstract_html":"Over the last few decades, considerable attention has been given to the development of lead-based ferroelectric systems such as PbZr1-xTixO3 due to their robust high temperature ferroelectric properties, as well as the presence of the so-called morphotropic phase boundary (MPB) ̶ a temperature-independent composition-driven structural instability that results in superior dielectric and piezoelectric properties. However, increasing environmental concerns are driving efforts towards the development of lead-free ferroelectrics such as BiFeO3, BaTiO3, and others. Previous work on epitaxial BiFeO3 thin films have shown that large compressive strains can drive the formation of complex mixed-phase structures with enhanced electromechanical responses (4-5% strains). In this work, we probe the nanoscale distribution of phases present in these mixed-phase structures using a combination of epitaxial thin-film growth and characterization techniques such as x-ray diffraction and piezoresponse force microscopy. We show, for the first time, the presence of monoclinic distortions and intermediate phases (akin to conventional MPB systems) in the mixed-phase films that are crucial for enhanced electromechanical responses. We then present thickness- and temperature- dependent phase-evolution studies that indicate the presence of a strain-spinodal between the various structural polymorphs of BiFeO3 to be the origin of mixed-phase formation. Finally, we discuss limitations due to a breakdown in epitaxy that occurs in thicker films and present chemical alloying-based approaches to mitigate these challenges. Having highlighted strain relaxation with increasing film thickness as a fundamental limitation to epitaxial-strain control, we explore an alternative route involving the use of a combination of defect-engineering and epitaxial strain to stabilize enhanced deformation states in materials. For this, we present a systematic study of BaTiO3 thin films, and show that epitaxial strain can be used to control the ordering of growth-induced defects driving deterministic additional out-of-plane strains that can enhance the ferroelectric Curie temperature to values exceeding 800°C without any need to change substrates. Such a combined control of epitaxial strain and engineered defect-structures provides a new pathway to extend the limits of strain-control of materials and properties. Lastly, we investigate a new route involving the use of epitaxial strain in conjunction with controlled composition- and strain- gradients to tune the thermal stability of dielectric responses of ferroelectric thin films. We present preliminary studies that reveal enhanced relative dielectric permittivity values of ~750, that change by less than 10% over a wide temperature range from 25-350ºC in compositionally-graded epitaxial BaxSr1-xTiO3 thin films, which is promising for next-generation microwave applications.","abstract_has_math":false,"creators":["Rama Damodaran, Anoop"],"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":["Martin, Lane W.","Cahill, David G.","Zuo, Jian-Min","Cooper, S. Lance"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2014,"date_issued":"2014-09-16T17:12:28Z","date_published":"2014-09-16T17:12:28Z","updated_at":"2026-07-22T22:25:40Z","subjects":["bismuth ferrite (BiFeO3)","thin films","electromechanical responses","phase transitions","barium titanate (BaTiO3)","BaxSr1-xTiO3","Lead-free","Epitaxy","Crystal structure"],"languages":["en"],"rights":["Copyright 2014 Anoop Rama Damodaran"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/50388","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Martin, Lane W.","Cahill, David G.","Zuo, Jian-Min","Cooper, S. 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However, increasing environmental concerns are driving efforts towards the development of lead-free ferroelectrics such as BiFeO3, BaTiO3, and others. Previous work on epitaxial BiFeO3 thin films have shown that large compressive strains can drive the formation of complex mixed-phase structures with enhanced electromechanical responses (4-5% strains). In this work, we probe the nanoscale distribution of phases present in these mixed-phase structures using a combination of epitaxial thin-film growth and characterization techniques such as x-ray diffraction and piezoresponse force microscopy. We show, for the first time, the presence of monoclinic distortions and intermediate phases (akin to conventional MPB systems) in the mixed-phase films that are crucial for enhanced electromechanical responses. We then present thickness- and temperature- dependent phase-evolution studies that indicate the presence of a strain-spinodal between the various structural polymorphs of BiFeO3 to be the origin of mixed-phase formation. Finally, we discuss limitations due to a breakdown in epitaxy that occurs in thicker films and present chemical alloying-based approaches to mitigate these challenges. Having highlighted strain relaxation with increasing film thickness as a fundamental limitation to epitaxial-strain control, we explore an alternative route involving the use of a combination of defect-engineering and epitaxial strain to stabilize enhanced deformation states in materials. For this, we present a systematic study of BaTiO3 thin films, and show that epitaxial strain can be used to control the ordering of growth-induced defects driving deterministic additional out-of-plane strains that can enhance the ferroelectric Curie temperature to values exceeding 800°C without any need to change substrates. Such a combined control of epitaxial strain and engineered defect-structures provides a new pathway to extend the limits of strain-control of materials and properties. Lastly, we investigate a new route involving the use of epitaxial strain in conjunction with controlled composition- and strain- gradients to tune the thermal stability of dielectric responses of ferroelectric thin films. We present preliminary studies that reveal enhanced relative dielectric permittivity values of ~750, that change by less than 10% over a wide temperature range from 25-350ºC in compositionally-graded epitaxial BaxSr1-xTiO3 thin films, which is promising for next-generation microwave applications.","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-07-15T17:31:50Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Rama Damodaran_Anoop.pdf: 7610290 bytes, checksum: 170c6437e2866ece2f44ad038f192a64 (MD5)","Made available in DSpace on 2014-09-16T17:12:28Z (GMT). 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In this work, we probe the nanoscale distribution of phases present in these mixed-phase structures using a combination of epitaxial thin-film growth and characterization techniques such as x-ray diffraction and piezoresponse force microscopy. We show, for the first time, the presence of monoclinic distortions and intermediate phases (akin to conventional MPB systems) in the mixed-phase films that are crucial for enhanced electromechanical responses. We then present thickness- and temperature- dependent phase-evolution studies that indicate the presence of a strain-spinodal between the various structural polymorphs of BiFeO3 to be the origin of mixed-phase formation. Finally, we discuss limitations due to a breakdown in epitaxy that occurs in thicker films and present chemical alloying-based approaches to mitigate these challenges. Having highlighted strain relaxation with increasing film thickness as a fundamental limitation to epitaxial-strain control, we explore an alternative route involving the use of a combination of defect-engineering and epitaxial strain to stabilize enhanced deformation states in materials. For this, we present a systematic study of BaTiO3 thin films, and show that epitaxial strain can be used to control the ordering of growth-induced defects driving deterministic additional out-of-plane strains that can enhance the ferroelectric Curie temperature to values exceeding 800°C without any need to change substrates. Such a combined control of epitaxial strain and engineered defect-structures provides a new pathway to extend the limits of strain-control of materials and properties. Lastly, we investigate a new route involving the use of epitaxial strain in conjunction with controlled composition- and strain- gradients to tune the thermal stability of dielectric responses of ferroelectric thin films. We present preliminary studies that reveal enhanced relative dielectric permittivity values of ~750, that change by less than 10% over a wide temperature range from 25-350ºC in compositionally-graded epitaxial BaxSr1-xTiO3 thin films, which is promising for next-generation microwave applications.","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-07-15T17:31:50Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Rama Damodaran_Anoop.pdf: 7610290 bytes, checksum: 170c6437e2866ece2f44ad038f192a64 (MD5)","Made available in DSpace on 2014-09-16T17:12:28Z (GMT). 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