Nonlinear optical studies of structural defects in perovskite dielectric and ferroelectric oxides for energy storage applications
Başlık çevirisi mevcut değil.
- Tez No: 598170
- Danışmanlar: PROF. NICHOLAS MADAMOPOULOS
- Tez Türü: Doktora
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2018
- Dil: İngilizce
- Üniversite: The City University of New York
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 131
Özet
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Özet (Çeviri)
Perovskite-type oxides have been recognized as promising candidates for energy storage applications due to their unique dielectric and material properties. In order to improve the performance of ceramic capacitors based titanites, it is essential to understand the voltage-induced dielectric breakdown and electrical energy storage limitations. In this thesis, we utilize optical second harmonic generation (SHG) and time-resolved pump-probe spectroscopy to investigate: 1-) structural defects due to migration of oxygen ions and vacancies near the interfaces of degraded Fe-doped SrTiO3 single crystals, 2-) the distribution of nanoscale structural distortions due to oxygen vacancy migration in electrodegraded Fe:STO single crystals, and 3-) the mixed tetragonal and rhombohedral phases in the ferroelectric Zr-doped BaTiO3 (BZT) film which exhibits outstanding energy recycling density and efficiency. First, the structural distortions across the anode and cathode interfaces of degraded reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals were detected by our optical SHG polarimetry. We revealed that the formation of structural inhomogeneity in both crystals is due to the local interaction of Fe4+ - oxygen ions and Fe3+ - oxygen vacancies near the degraded anode and cathode interfaces, respectively. The results are associated with the formation of centrosymmetric Fe4+:Ti4+-O6 octahedral structures and non-centrosymmetric Jahn-Teller distortions in the reduced and the oxidized anode, respectively. The structural distortions, Fe4+ concentration changes, and oxygen vacancy accumulation across the probe regions were further verified by confocal Raman spectroscopy. Second, the distribution of nanoscale structural defects in electrodegraded Fe-doped SrTiO3 (Fe:STO) single crystals is directly revealed by ultrafast photoacoustic waves. We utilized time-resolved reflectance spectra to nondestructively characterize local structural distortions near the degraded anode and cathode interfaces in both the reduced and oxidized crystals. We show that an accumulation of oxygen vacancies resulted in significant structural deformations near the degraded cathode interface of the reduced crystal. The defect distribution shows a strong dependence on oxygen vacancy concentration and diffusion within the crystals. Third, the heterophase polydomain structures in ferroelectric BZT films were investigated using optical SHG and time-resolved pump-probe spectroscopy. We analyzed the spatial distribution of SHG intensities and GHz acoustic phonon oscillations. A rhombohedral symmetry is revealed to grow with increasing film thickness as tetragonal domains relax away from the film-substrate interface. The presence of phase segregated tetragonal and rhombohedral structures is further confirmed through TEM and XRD measurements. The high energy performance of the films is explained by ultra-adaptive nanodomains which can effectively accommodate the competing elastic and electrical stress fields during charge-discharge cycles.
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