Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Determination of the Electrocalorinc Properties of the Ferroelectric (1-x)batio3-bi(li1/3ti2 (0?x?0.2) System(Izmir Institute of Technology, 2018) Demirtay, Tuğçe; Adem, Umut; Çiftçioğlu, MuhsinThe aim of this study is to develop electrocaloric (EC) materials for alternative eco-friendly cooling technologies. Considering the dielectric and piezoelectric properties of the (1-x)BaTiO3- xBi(Li1/3Ti2/3)O3 (0≤x≤0.2), this system was selected to study electrocaloric properties due to the presence of morphotropic phase boundary (MBP). The crystal structure of the samples that were synthesized by convential solid state reaction technique were determined by the X-Ray Diffraction experiments. The electrical properties of the ceramics were characterized by temperature-dependent dielectric measurements and the phase transition temperatures of the samples were identified. Temperature-dependent electrical polarization curves were measured for all compositions and electrocaloric temperature change values were calculated with the help of Maxwell equations. Using the dielectric measurements, a phase diagram was obtained. Strain-electric field measurements were done to complement dielectric and polarization measurements. A new antiferroelectric phase was discovered at high temperatures in the samples. As Bi(Li1/3Ti2/3)O3 content is increased, phase transition from the ferroelectric to antiferroelectric phase decreases. Since in the antiferroelectric phase the net polarization is very small, a large polarization change therefore large electrocaloric temperature change is obtained. Highest electrocaloric temperature change (ΔT=0.66 K under 22 kV/cm) is obtained for x=0.03 sample.Master Thesis Batio3 Based Ferroelectric Materials for Electrocaloric Cooling Applications(Izmir Institute of Technology, 2018) Şanlı, Keriman; Adem, Umut; Akdoğan, YaşarThe aim of this project was to produce electrocaloric materials and to determine the potential of these materials for electrocaloric cooling applications. The electrocaloric effect (ECE) of lead-free Ba0.8Sr0.2Ti1-xZrxO3 (0 ≤ x ≤ 0.10) ferroelectric ceramics was studied. The phase analysis of each ceramic composition that was synthesized by conventional solid-state reaction technique was performed by X-ray Diffraction. Dielectric measurements were done to determine the phase transition temperatures (Curie temperature, Tc) of all compositions and also construct a phase diagram. ΔT values were calculated indirectly using electrical polarization curves measured at different temperatures and Maxwell's equations. ΔT values that were obtained from different regions of the phase diagram are compared. The most suitable composition for applications was chosen considering the ΔT value, temperature range where relatively large ΔT is preserved and the Curie temperature of all ceramics. Ba0.8Sr0.2Ti0.93Zr0.07O3 ceramic located near the critical point shows the best performance with ΔT value of 0.40 K under 20 kV/cm. In comparison with the lead-free ceramics studied in the literature, Ba0.8Sr0.2Ti1-xZrxO3 system can be considered as one of the best candidates for future electrocaloric cooling technologies.