Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Lead-Free Ferroelectric Ceramics for Energy Storage and Electrocaloric Cooling Applications(01. Izmir Institute of Technology, 2022) Karakaya, Merve; Karakaya, Merve; Adem, Umut; Adem, UmutThis thesis study consists of five main chapters that include an introduction about the principles and applications of ferroelectrics and four chapters on different lead-free ferroelectric ceramic systems developed for the energy storage and electrocaloric cooling applications. In the first chapter, the principles of ferroelectricity and dielectric, piezoelectric and pyroelectric properties of ferroelectrics are introduced followed by the applications considered in this thesis: Electrocaloric cooling and capacitive energy storage. In the second chapter, the effects of bismuth lithium titanate incorporation into sodium bismuth titanate-barium titanate systems on the energy storage properties have been discussed. In addition, it has been calculated that these compositions have improved energy storage properties close to the high values obtained in the literature. In the third chapter, the effect of two different manganese precursors on the probability of defect dipole formation, ferroelectric aging and resulting manganese valences of ceramics were investigated by manganese doping on barium strontium titanate base ceramics. In addition, their electrocaloric properties were investigated by indirect method. In the fourth chapter, electrocaloric properties of barium titanate - sodium bismuth titanate systems has been investigated. The increase in tetragonality by sodium bismuth titanate incorporation has been verified by Rietveld refinement and those compositions were shown to be suitable for electrocaloric applications. In the fifth chapter, a sodium bismuth titanate - potasium bismuth titanate composition which is in morphotropic phase boundary, was synthesized by templated grain growth method, and the effect of orientation on the electrocaloric effect was investigated by direct and indirect measurements.Doctoral Thesis Improvement of It-Sofc by Tailoring the Microstructure of Lscf Cathode and Gdc Electrolyte(Izmir Institute of Technology, 2019) Sındıraç, Can; Akkurt, Sedat; Büyükaksoy, AligülThe high operating temperature of solid oxide fuel cells (SOFC) brings about some restrictions like the high cost of fuel cell, long start-up time, thermal stress, and decreasing lifetime. Thus, lowering the operating temperature is vital for improvement of SOFC. However, reducing the operating temperature leads to some negative effects on solid oxide fuel cell performance by increasing the electrolyte and electrode resistances. This dissertation focuses on tailoring the cathode and/or electrolyte layers to obtain improved electrochemical performances. For this purpose, some strategies are proposed. These are (i) thin film cathode nanocomposite cathode layer formation, (ii) infiltration of porous GDC by LSCF/LSCF+GDC, (iii) infiltration of porous GDC by GDC solution to improve densification at lower temperature and finally (iv) electrochemical characterization of GDC densified by infiltration.