Gehringer, Maximilian (2024)
Prototyping lead-free Na₀.₅Bi₀.₅TiO₃-based multilayer ceramic capacitors.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00026501
Dissertation, Erstveröffentlichung, Verlagsversion
Kurzbeschreibung (Abstract)
Multilayer ceramic capacitors (MLCCs) that can withstand high temperatures and voltages are urgently needed for upcoming high-temperature (HT) power electronics applications like renewable energies, power conversion, and electric vehicles. While environmental conditions usually do not exceed 300 °C, voltage requirements and limits for capacitors under operation are often uncertain. Thus, the stability of electrical properties in a broad range of operating conditions is required. Lead zirconate titanate (PZT)-based capacitors cannot be utilized due to the toxicity of lead and environmental concerns. Commercial lead-free BaTiO₃ (BT)-based ceramic capacitors are limited to 190 °C. Capacitor materials based on Na₀.₅Bi₀.₅TiO₃ (NBT) are promising contenders, but their complex defect chemistry has to be assessed. Especially since oxygen vacancy migration during operation is one of the most critical aspects. In MLCCs that operate under temperature and voltage stress, additional migration of the inner electrode material into the dielectric needs to be considered. This well-known issue in lead-based components with silver-palladium (Ag/Pd) electrodes can cause severe electrodegradation and lower reliability. While similar effects are expected for NBT-based MLCCs, the actual mechanism for this complex electrodegradation is investigated. Capacitors are prepared using the MLCC fabrication route, comprised of slurry preparation, tape casting, shaping processes, and thermal treatment of green bodies. This work aims to provide an integral approach to optimizing the manufacturing processes of NBT-based MLCCs co-fired with Ag/Pd electrodes. Four key influencing factors are evaluated: slurry composition, shaping processes, sintering conditions, and electrode material. Ultimately, the prepared prototype MLCCs exhibit a homogeneous microstructure with low porosity and excellent lamination of individual layers and electrodes. They feature an exceptional operational window regarding temperature (-67 to 375 °C) and voltage (up to 1.5 kV), with only a slight variation of capacitance (≤±10%). Voltage ratings do not have to be specified due to this high voltage insensitivity. The prototype MLCCs with Ag/Pd electrodes exhibit greater resilience against enhanced degradation. Moreover, a novel indentation method was conceptualized to evaluate the dielectric breakdown strength (DBS), excluding extrinsic effects and identifying areas with electric field concentrations. Here, NBT-based MLCCs are more limited by the component’s design than by the dielectric strength of the ceramic. This work demonstrates the remarkable stability of NBT-based prototype MLCCs against high temperatures and voltages, making them strong candidates for future high-temperature and power electronics applications.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2024 | ||||
Autor(en): | Gehringer, Maximilian | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Prototyping lead-free Na₀.₅Bi₀.₅TiO₃-based multilayer ceramic capacitors | ||||
Sprache: | Englisch | ||||
Referenten: | Frömling, Dr. Till ; Klein, Prof. Dr. Andreas ; Weidenkaff, Prof. Dr. Anke ; Malič, Prof. Dr. Barbara | ||||
Publikationsjahr: | 24 Januar 2024 | ||||
Ort: | Darmstadt | ||||
Kollation: | xx, 163 Seiten | ||||
Datum der mündlichen Prüfung: | 6 Dezember 2023 | ||||
DOI: | 10.26083/tuprints-00026501 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/26501 | ||||
Kurzbeschreibung (Abstract): | Multilayer ceramic capacitors (MLCCs) that can withstand high temperatures and voltages are urgently needed for upcoming high-temperature (HT) power electronics applications like renewable energies, power conversion, and electric vehicles. While environmental conditions usually do not exceed 300 °C, voltage requirements and limits for capacitors under operation are often uncertain. Thus, the stability of electrical properties in a broad range of operating conditions is required. Lead zirconate titanate (PZT)-based capacitors cannot be utilized due to the toxicity of lead and environmental concerns. Commercial lead-free BaTiO₃ (BT)-based ceramic capacitors are limited to 190 °C. Capacitor materials based on Na₀.₅Bi₀.₅TiO₃ (NBT) are promising contenders, but their complex defect chemistry has to be assessed. Especially since oxygen vacancy migration during operation is one of the most critical aspects. In MLCCs that operate under temperature and voltage stress, additional migration of the inner electrode material into the dielectric needs to be considered. This well-known issue in lead-based components with silver-palladium (Ag/Pd) electrodes can cause severe electrodegradation and lower reliability. While similar effects are expected for NBT-based MLCCs, the actual mechanism for this complex electrodegradation is investigated. Capacitors are prepared using the MLCC fabrication route, comprised of slurry preparation, tape casting, shaping processes, and thermal treatment of green bodies. This work aims to provide an integral approach to optimizing the manufacturing processes of NBT-based MLCCs co-fired with Ag/Pd electrodes. Four key influencing factors are evaluated: slurry composition, shaping processes, sintering conditions, and electrode material. Ultimately, the prepared prototype MLCCs exhibit a homogeneous microstructure with low porosity and excellent lamination of individual layers and electrodes. They feature an exceptional operational window regarding temperature (-67 to 375 °C) and voltage (up to 1.5 kV), with only a slight variation of capacitance (≤±10%). Voltage ratings do not have to be specified due to this high voltage insensitivity. The prototype MLCCs with Ag/Pd electrodes exhibit greater resilience against enhanced degradation. Moreover, a novel indentation method was conceptualized to evaluate the dielectric breakdown strength (DBS), excluding extrinsic effects and identifying areas with electric field concentrations. Here, NBT-based MLCCs are more limited by the component’s design than by the dielectric strength of the ceramic. This work demonstrates the remarkable stability of NBT-based prototype MLCCs against high temperatures and voltages, making them strong candidates for future high-temperature and power electronics applications. |
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Alternatives oder übersetztes Abstract: |
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Status: | Verlagsversion | ||||
URN: | urn:nbn:de:tuda-tuprints-265014 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 530 Physik 500 Naturwissenschaften und Mathematik > 540 Chemie 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau 600 Technik, Medizin, angewandte Wissenschaften > 621.3 Elektrotechnik, Elektronik |
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Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Nichtmetallisch-Anorganische Werkstoffe |
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TU-Projekte: | PTJ|03XP0146|HTL-NBT Nachwuchsgru | ||||
Hinterlegungsdatum: | 24 Jan 2024 14:16 | ||||
Letzte Änderung: | 25 Jan 2024 06:23 | ||||
PPN: | |||||
Referenten: | Frömling, Dr. Till ; Klein, Prof. Dr. Andreas ; Weidenkaff, Prof. Dr. Anke ; Malič, Prof. Dr. Barbara | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 6 Dezember 2023 | ||||
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