Khachaturyan, Ruben (2019)
POLARIZATION SWITCHING KINETICS IN FERROELECTRIC CERAMICS.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
The classical Kolmogorov-Avrami-Ishibashi (KAI) model successfully describes polarization switching kinetics of single crystals. Later on, Tagantsev et al. introduced a statistical distribution of switching time (SwT) in the KAI model; the improved statistical model is known as the nucleation limited switching (NLS) model and became suitable for thin films. Based on a robust dependence of SwT on an electric field, Lupascu et al. have proposed that the nature of the SwT statistical distribution can be attributed to a corresponding distribution of local electric fields inside a material. Using this assumption, the inhomogeneous field mechanism (IFM) model was developed. Although the NLS and IFM models are able to describe experimental measurements with high accuracy they neglect several crucial physical aspects of the poling problem. A disordered granular structure in a polarized state is unavoidably accompanied by charge formation on grain boundaries (GB), therefore giving rise to additional electric fields. Charges on grain boundaries should vary depending on polarization, therefore depolarization fields should be also time dependent. The latter fact, however, is omitted in the NLS as well as in the IFM models. Another questionable assumption, included in all statistical models, is the statistical independence of switching regions, which is doubtful since the huge depolarization fields have to produce grain correlations. Statistical independence of switching events disable accounting for non-180 switching events because these events are sequential processes rather than independent. Hence an independent switching mechanism is not suitable for this process. These all make the aforementioned statistical models and the reliability of extracted parameters questionable. This work aims to shed some light on the reliability of statistical models by investigation of charge formation on grain boundaries during a poling process as well as produced depolarization fields and their evolution. Correlations of polarization and electric field components are analyzed. All studies are carried out for tetragonal, rhombohedral and orthorhombic symmetries and are in good agreement with previous theoretical results and experimental measurements. A new statistical model which involves non-180 switching events is presented and successfully applied to the recent polarization-time and strain-time measurements. A statistical distribution of electric fields is additionally studied for the case of porous ceramics as they are materials where the distribution can be controlled by modifications to the structure.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2019 | ||||
Autor(en): | Khachaturyan, Ruben | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | POLARIZATION SWITCHING KINETICS IN FERROELECTRIC CERAMICS. | ||||
Sprache: | Englisch | ||||
Referenten: | Genenko, Apl. Prof. Yuri ; Hongbin, Prof. Zhang | ||||
Publikationsjahr: | 19 März 2019 | ||||
Ort: | Darmstadt | ||||
Datum der mündlichen Prüfung: | 17 Dezember 2018 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/8572 | ||||
Kurzbeschreibung (Abstract): | The classical Kolmogorov-Avrami-Ishibashi (KAI) model successfully describes polarization switching kinetics of single crystals. Later on, Tagantsev et al. introduced a statistical distribution of switching time (SwT) in the KAI model; the improved statistical model is known as the nucleation limited switching (NLS) model and became suitable for thin films. Based on a robust dependence of SwT on an electric field, Lupascu et al. have proposed that the nature of the SwT statistical distribution can be attributed to a corresponding distribution of local electric fields inside a material. Using this assumption, the inhomogeneous field mechanism (IFM) model was developed. Although the NLS and IFM models are able to describe experimental measurements with high accuracy they neglect several crucial physical aspects of the poling problem. A disordered granular structure in a polarized state is unavoidably accompanied by charge formation on grain boundaries (GB), therefore giving rise to additional electric fields. Charges on grain boundaries should vary depending on polarization, therefore depolarization fields should be also time dependent. The latter fact, however, is omitted in the NLS as well as in the IFM models. Another questionable assumption, included in all statistical models, is the statistical independence of switching regions, which is doubtful since the huge depolarization fields have to produce grain correlations. Statistical independence of switching events disable accounting for non-180 switching events because these events are sequential processes rather than independent. Hence an independent switching mechanism is not suitable for this process. These all make the aforementioned statistical models and the reliability of extracted parameters questionable. This work aims to shed some light on the reliability of statistical models by investigation of charge formation on grain boundaries during a poling process as well as produced depolarization fields and their evolution. Correlations of polarization and electric field components are analyzed. All studies are carried out for tetragonal, rhombohedral and orthorhombic symmetries and are in good agreement with previous theoretical results and experimental measurements. A new statistical model which involves non-180 switching events is presented and successfully applied to the recent polarization-time and strain-time measurements. A statistical distribution of electric fields is additionally studied for the case of porous ceramics as they are materials where the distribution can be controlled by modifications to the structure. |
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URN: | urn:nbn:de:tuda-tuprints-85725 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 530 Physik |
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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 Materialmodellierung |
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Hinterlegungsdatum: | 07 Apr 2019 19:55 | ||||
Letzte Änderung: | 07 Apr 2019 19:55 | ||||
PPN: | |||||
Referenten: | Genenko, Apl. Prof. Yuri ; Hongbin, Prof. Zhang | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 17 Dezember 2018 | ||||
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