Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 5Citation - Scopus: 6Formation of Monolithic Srtio3-Tio2 Ceramic Heterostructures by Reactive Hydrothermal Sintering(Elsevier, 2023) Karacasulu, Levent; Kartal, Uğur; İçin, Öykü; Bortolotti, Mauro; Biesuz, Mattia; Ahmetoğlu, Çekdar VakıfIn a one-pot approach, monolithic SrTiO3-TiO2 ceramic heterostructures were obtained using the reactive hydrothermal liquid phase densification (rHLPD). Structural, morphological, and photocatalytic properties of the obtained ceramics were analyzed. The relative density of the formed components reached about 80% with reaction time, temperature, and NaOH concentration variation. It was observed via Rietveld refinement that there was no XRD detectable phase other than TiO2 and SrTiO3 in the final structure. The monolithic SrTiO3-TiO2 ceramics obtained by hydrothermal reaction at 120 °C for 24 h in 1 M NaOH concentration showed a dielectric constant being around 500, and the dielectric loss was below 0.25 at frequencies higher than 10 kHz. The SrTiO3-TiO2 heterostructured monoliths having only 20 vol% total porosity and low specific surface area, demonstrated ∼60% efficiency (in 5 h) in degrading Methylene Blue photo-catalytically. © 2023 Elsevier LtdArticle Citation - WoS: 7Citation - Scopus: 7Hydrothermal Synthesis of Potassium–sodium Niobate Powders(Wiley, 2022) Pişkin, Cerem; Karacasulu, Levent; Ischia, Gloria; Bortolotti, Mauro; Ahmetoğlu, Çekdar VakıfPotassium–sodium niobates (KxNa1−xNbO3, 0 < x < 1, KNN) were hydrothermally synthesized under varying alkaline ratios (K+/Na+), total hydroxide concentration, reaction temperature, and time. Compositional surveys were developed by using Rietveld analyses derived quantitative volume fractions. The data demonstrated that phase pure KNN synthesis can be achieved by reacting the niobium source with the hydroxide solution having 6 M total hydroxide concentration, cation ratio (K+/Na+) of above 6 at temperatures ≥200°C for 24 h. Dissolution–precipitation events through intermediate products including hexaniobates were postulated as a plausible formation mechanism. It was shown also that the single-phase KNN approaching the morphotropic phase boundary (MPB) could be obtained by further incorporation of sodium ions into the crystal via post-annealing at 800°C/2 h, following the hydrothermal synthesis.Article Citation - WoS: 19Citation - Scopus: 21Synthesis and Additive Manufacturing of Calcium Silicate Hydrate Scaffolds(Elsevier, 2021) Oğur, Ezgi; Botti, Renata; Bortolotti, Mauro; Colombo, Paolo; Ahmetoğlu, Çekdar VakıfA Calcium silicate hydrate (CSH) powder containing above 60 wt% xonotlite (remaining being tobermorite, scawtite and calcite) were produced from lime and ordinary recycled soda-lime glass via simple hydrothermal synthesis route. The thermogravimetric analysis demonstrated only similar to 20%weight loss up to 800 degrees C (at about the transformation temperature of CSHs to wollastonite), reaching a plateau in the 800-1200 degrees C temperature range. The synthesized CSH powder was employed for the fabrication of both green and heat-treated scaffolds by additive manufacturing (AM), possessing a high porosity (>80 vol%) and limited strength (similar to 0.9 MPa). (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Article Citation - WoS: 8Citation - Scopus: 12Synthesis of Potassium-Sodium Niobate (Knn) From Nbo2(Elsevier, 2021) Piskin, Cerem; Karacasulu, Levent; Bortolotti, Mauro; Vakifahmetoglu, CekdarKxNa1-xNbO3 (0 < x < 1) were synthesized via hydrothermal method using niobium dioxide (NbO2) as the niobium source instead of the most common one, Nb2O5. Potassium-rich KxNa1-xNbO3 (x > 0.5) was obtained from 8 M total hydroxide concentration after 6 h of reaction at 200 degrees C. Rietveld refinement of the XRD data revealed that all samples exhibited the secondary NaNbO3 phase. However, the lowest amount (3.74 vol%) was obtained for 24 h of reaction under 10 M alkaline solution. After 3 h of reaction, dodecahedra shaped hexaniobate phase (KxNa8-xNb6O19.nH(2)O) was observed. Those structures were, subsequently, replaced by similar to 3 mu m cube shaped KNN crystals, obtained under 10 M reaction in 24 h time period.Article Citation - WoS: 14Citation - Scopus: 17Electrical Characteristics of Low Temperature Densified Barium Titanate(Elsevier, 2020) Karacasulu, Levent; Tokkan, Melike; Bortolotti, Mauro; Ischia, Gloria; Adem, Umut; Ahmetoğlu, Çekdar VakıfA low temperature densification technique, i.e. reactive hydrothermal liquid-phase densification (rHLPD) was followed to obtain highly dense BaTiO3 components at temperatures <= 240 degrees C. The formed ceramics were characterized concerning not only the structural features but also the electrical properties. The increase of both reaction time and temperature resulted in enhanced densification of BaTiO3 components reaching about 90% of theoretical density. The presence of the tetragonal BaTiO3 was demonstrated by both XRD and TEM analysis. Despite the low reaction temperatures, the samples showed promising dielectric, ferroelectric and piezoelectric functionality without additional annealing. A broad dielectric peak was observed around 135 degrees C at the Curie temperature; saturated hysteresis loops and corresponding butterfly-shaped strain-electric field loops were obtained. BaTiO3 sample subjected to hydrothermal reaction at 240 degrees C for 72 h yielded a piezoelectric coefficient of 84 pC/N.