Karakaya, Merve
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01. Izmir Institute of Technology
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13
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11
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| Journal | Count |
|---|---|
| Journal of Materials Science: Materials in Electronics | 3 |
| Journal of the European Ceramic Society | 2 |
| Journal of Materials Chemistry C | 2 |
| Nanostructured Solar Cells | 1 |
| AIP Advances | 1 |
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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.Article Citation - WoS: 3Citation - Scopus: 2Electrocaloric Behaviour of Tape Cast and Grain Oriented Nbt-Kbt Ceramics(Elsevier Sci Ltd, 2024) Unal, Muhammet Ali; Karakaya, Merve; Irmak, Tugce; Yildirim-Ozarslan, Gokce; Avci, A. Murat; Fulanovic, Lovro; Adem, UmutWe have investigated the effects of grain orientation and tape casting process on the electrocaloric properties of 0.82Na(0.5)Bi(0.5)TiO(3)-0.18 K0.5Bi0.5TiO3 (0.82NBT-0.18KBT) ceramics at the Morphotropic Phase Boundary (MPB), using direct and indirect measurements. We observe a larger electrocaloric response for the template-free ceramics compared to 7 and 10 wt% template containing ones, suggesting that grain orientation along rhombohedral < 100 > does not improve the electrocaloric response. Indirect measurements yielded a large adiabatic temperature change of around 3 K under an electric field of 50 kV/cm, which is significantly higher than 0.9 K reached at a lower electric field of 40 kV/cm using the direct measurement.Article Citation - WoS: 3Citation - Scopus: 3Novel Injectable Calcium-Magnesium Phosphate Cement-Based Composites With Piezoelectric Properties: Advancements in Bone Regeneration Applications(Springer, 2024) Sakar, Neslihan; Albayrak, Aylin Ziylan; Karakaya, Merve; Adem, Umut; Tansel, TunayDesigning a novel injectable bone cement is an important approach to the success of bone healing in minimally invasive surgeries. As natural bone has a piezoelectric property, which is crucial in bone regeneration, this study focused on the development of a novel injectable composite bone cement with piezoelectric properties. For the composite composition, calcium and zirconium doped barium titanate (BCZT) was used for its piezoelectric property, while calcium phosphate and magnesium phosphate cement (CMPC) were preferred for its bone-like properties. In this framework, first BCZT, CMPC, and their composites were prepared, and their phase structures, particle size distributions, and piezoelectric and dielectric properties were investigated. Then, the composite bone cements were prepared by mixing CMPC with BCZT in three different ratios (20%, 30%, and 40%). Next, polysorbate 80 solution was added to the cement mixtures to prepare the injectable pastes. Finally, injectability, setting time, and compressive strength of the composites were assessed. As a result, the composite bone cement containing 30% BCZT has the potential to be used as an injectable bone cement in invasive orthopedic surgery.Article Citation - WoS: 2Citation - Scopus: 2Surface Roughness Estimation of Mbe Grown Cdte/Gaas(211)b by Ex-Situ Spectroscopic Ellipsometry(American Institute of Physics, 2016) Karakaya, Merve; Bilgilisoy, Elif; Arı, Ozan; Selamet, YusufSpectroscopic ellipsometry (SE) ranging from 1.24 eV to 5.05 eV is used to obtain the film thickness and optical properties of high index (211) CdTe films. A three-layer optical model (oxide/CdTe/GaAs) was chosen for the ex-situ ellipsometric data analysis. Surface roughness cannot be determined by the optical model if oxide is included. We show that roughness can be accurately estimated, without any optical model, by utilizing the correlation between SE data (namely the imaginary part of the dielectric function, <ϵ2 > or phase angle, ψ) and atomic force microscopy (AFM) roughness. <ϵ2 > and ψ values at 3.31 eV, which corresponds to E1 critical transition energy of CdTe band structure, are chosen for the correlation since E1 gives higher resolution than the other critical transition energies. On the other hand, due to the anisotropic characteristic of (211) oriented CdTe surfaces, SE data (<ϵ2 > and ψ) shows varieties for different azimuthal angle measurements. For this reason, in order to estimate the surface roughness by considering these correlations, it is shown that SE measurements need to be taken at the same surface azimuthal angle. Estimating surface roughness in this manner is an accurate way to eliminate cumbersome surface roughness measurement by AFM.Article Citation - WoS: 3Citation - Scopus: 3Effects of Different Precursors on the Aging and Electrocaloric Properties of Mn-Doped Ba0.95sr0.05tio3 Ceramics(Springer, 2023) Karakaya, Merve; Erdem, Emre; Akdoğan, Yaşar; Adem, UmutIn this study, the effects of different types of Mn precursors (MnO2 and Mn2O3) and sintering temperature on the defect dipole formation, ferroelectric aging and electrical properties were investigated by using Ba0.95Sr0.05TiO3 ceramics as the base. Both Mn precursors were substituted to the Ti-site as 1 mol% and two different sintering temperatures of 1325 and 1400 degrees C were used to study the effect of grain size. We deduced that slightly higher amounts of Mn2+ can be incorporated into the perovskite structure when MnO2 is used as the precursor, by using X-ray diffraction and electron paramagnetic resonance spectroscopy. Mn-doped samples sintered at 1325 degrees C age faster than those sintered at 1400 degrees C. Aging caused a decrease in the electrocaloric effect whereas Mn-doping increased it. This study shows that Mn precursor used for the acceptor doping affects the amount of Mn incorporated into the structure and therefore electrical properties of the resulting ceramics.Article Citation - WoS: 3Citation - Scopus: 3Growth and Characterization of Cdte Absorbers on Gaas by Mbe for High Concentration Pv Solar Cells(John Wiley and Sons Inc., 2015) Arı, Ozan; Polat, Mustafa; Karakaya, Merve; Selamet, YusufCdTe based II-VI absorbers are promising candidates for high concentration PV solar cells with an ideal band gap for AM1.5 solar radiation. In this study, we propose single crystal CdTe absorbers grown on GaAs substrates with a molecular beam epitaxy (MBE) which is a clean deposition technology. We show that high quality CdTe absorber layers can be grown with full width half maximum of X-ray diffraction rocking curves (XRD RC) as low as 227 arc-seconds with 0.5% thickness uniformity that a 2 μm layer is capable of absorbing 99% of AM1.5 solar radiation. Bandgap of the CdTe absorber is found as 1.483 eV from spetroscopic ellipsometry (SE) measurements. Also, high absorption coefficient is calculated from the results, which is ∼5 x 105cm-1 in solar radiation spectrum.Article Citation - WoS: 11Citation - Scopus: 12Characterization of Cdte Growth on Gaas Using Different Etching Techniques(Springer Verlag, 2015) Bilgilisoy, Elif; Özden, Selin; Bakali, Emine; Karakaya, Merve; Selamet, YusufCdTe buffer layers which were grown on (211)B GaAs by molecular beam epitaxy were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The optical properties and thicknesses of the samples were obtained by ex situ spectroscopic ellipsometry. The surface morphologies of the CdTe epilayers were analyzed by atomic force microscopy, scanning electron microscopy, and Nomarski microscopy before and after chemical etching. We compare the triangle- and trapezoid-shaped etch pits due to the Everson and Nakagawa etch solutions, respectively. Measured etch pit density (EPD) values of triangle etch pits were found in the 8 × 107 cm−2 to 2 × 108 cm−2 range, and trapezoid-shaped etch pits were found in the 1 × 107 cm−2 to 7 × 107 cm−2 range for samples with thicknesses <2 μm.Book Part Citation - WoS: 11Recent Progresses in Perovskite Solar Cells(Intech Europe, 2017) Demiç, Şerafettin; Özcivan, Ahmet Nuri; Can, Mustafa; Özbek, Cebrail; Karakaya, MervePerovskite solar cell (PSC) can be regarded as a continuation of dye sensitized solar cell (DSSC) in terms of the sensitization phenomena that occurred in the functioning molecules. In 2012, a breakthrough propose has been made for the sensitization of PSCs, in which a solid-state structure is offered as an equivalent sensitizer used in DSSC. The power conversion efficiency (PCE) of those solid-state cells reached about twofold of its initial value during the past several years. Immediately after, the researchers followed this propose worldwide. They have introduced an improved efficiency of as much as 20%, which was originally started from its initial value of 4%, just in 4 years. Thus, the new concept, solid perovskite molecules, has eliminated the need for the liquid electrolyte in DSSC while still carrying the advantages of organic solar cells (OSCs). Therefore, the distinctive material of PSC-the organometallic halide molecules (also known as OMH or organic-inorganic trihalides)-inclined an unexpected reputation for solar cell (SC) researches. Hence, it seems that we will witness a new age for solar conversion devices depending on the recent hopeful progresses on PSCs. The high rate of photovoltaic (PV) conversion capacity in PSC is generally expressed by the basic properties possessed by the organic-inorganic perovskite crystal, such as better optical properties and well diffused charges along huge distances during the charge transport. In addition, a low temperature processing is applicable during its production. Moreover, the perovskite layer provides a tunable band gap. Therefore, depending on better developments on designed molecules, PSC may gain extreme performances compared to the other competitors, such as OSC or DSSC devices. This chapter starts with a general discussion on the need for an affordable clean energy conversion device that is urgent for the future of humanity, due to publicly well-known global warming issue. In Section 2, basic properties of PSC are mentioned together with their structure and working principles. Section 3 continues with an overview on organometallic perovskite molecules after a brief introductory history is presented. The absorption and band gap properties are also discussed. Since most perovskite materials need a hole transporting material (HTMs) within the PSC, the kinds of HTMs that are designed for PSCs are described in Section 3. The rendering of long-term stabilization has special importance for PSCs since the instability issue remained idle in spite of those recent increased efficiency values attained by various research groups. Therefore, the stability issues are discussed in a separate part in Section 4. We finally close the chapter discussing the challenges and opportunities relying on the chapter content. We note that the recent investigations on PSCs have special importance for its large-scale realization in order to make them ready for the photovoltaic industry of the future. Hence, there are various announced meetings focusing on its mass production due to the unexpected sharp rise of the perovskite efficiency in the last 6 years. Hence, all the new cutting-edge scientific findings are also dealt with commercialization issues now, in order to attain the desired low cost fabrication, including the yield of high purity and the formation of smooth films during the continual manufacture of perovskite layers.Article Citation - WoS: 3Citation - Scopus: 2Electrocaloric Behaviour of Tape Cast and Grain Oriented Nbt-Kbt Ceramics(Elsevier Sci Ltd, 2024) Unal, Muhammet Ali; Karakaya, Merve; Irmak, Tugce; Yildirim-Ozarslan, Gokce; Avci, A. Murat; Fulanovic, Lovro; Adem, UmutWe have investigated the effects of grain orientation and tape casting process on the electrocaloric properties of 0.82Na(0.5)Bi(0.5)TiO(3)-0.18 K0.5Bi0.5TiO3 (0.82NBT-0.18KBT) ceramics at the Morphotropic Phase Boundary (MPB), using direct and indirect measurements. We observe a larger electrocaloric response for the template-free ceramics compared to 7 and 10 wt% template containing ones, suggesting that grain orientation along rhombohedral < 100 > does not improve the electrocaloric response. Indirect measurements yielded a large adiabatic temperature change of around 3 K under an electric field of 50 kV/cm, which is significantly higher than 0.9 K reached at a lower electric field of 40 kV/cm using the direct measurement.Article Citation - WoS: 11Citation - Scopus: 11Enhanced Room Temperature Energy Storage Density of Bi(li1/3ti2 Substituted Bi0.5na0.5tio3-Batio3 Ceramics(IOP Publishing, 2021) Karakaya, Merve; Adem, UmutFor high power electronics applications, relaxor ferroelectrics are promising materials due to their superior energy storage properties. In this study, we investigate the energy storage properties of novel lead free relaxor ferroelectric ceramics (1-x)(0.92Bi(0.5)Na(0.5)TiO(3)-0.08BaTiO(3))-xBi(Li1/3Ti2/3)O-3 (abbreviated as BNT-8BT-xBLT). BNT-8BT composition which is close to morphotropic phase boundary was chosen as the base due to its large maximum polarization (P-m) and higher ratio of weakly polar tetragonal phase which is expected to facilitate ergodic relaxor behavior and improve energy storage density. The substitution of BLT to the BNT-8BT strongly disrupts the correlations between the polar nanoregions and the transition from nonergodic to ergodic relaxor state occurs already at x = 0.02 BLT at room temperature. Largest energy density (W-rec) at 61 kV cm(-1) was obtained for x = 0.02 sample (0.656 J cm(-3)), followed by x = 0.03 (W-rec = 0.614 J cm(-3)) and x = 0.05 (W-rec= 0.559 J cm(-3)). The x = 0.02 sample keeps its energy storage density at high temperatures (i.e. W-rec= 0.88 J cm(-3,) eta = 97%, E-m= 65 kV cm(-1) at 125 degrees C), while larger electric field (up to 89 kV cm(-1)) could be applied to the x = 0.05 sample with the smallest grain size and energy density of 1.03 J cm(-3) was reached at room temperature. Energy storage density values of BLT substituted materials normalized per unit applied electric field are promising among BNT-based materials.