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: 8Citation - Scopus: 8Fast-Firing of Potassium Sodium Niobate (knn)(Elsevier B.V., 2024) Karacasulu,L.; Karakaya,M.; Adem,U.; Sglavo,V.M.; Biesuz,M.; Vakifahmetoglu,C.Potassium sodium niobate (KNN) is one of the most promising Pb-free piezo-ceramics. In the present work, KNN was produced by fast-firing with different cooling strategies, i.e., fast and slow cooling. Dielectric, ferroelectric, and piezoelectric properties of fast-fired pellets were determined and compared with those of conventional-sintered products. Although the samples produced by fast-firing had higher density than those obtained by conventional sintering, fast-cooled samples following fast firing show relatively low electrical properties. When fast-firing was combined with slow cooling, the electrical properties, especially piezoelectric d33 values, were improved. The material subjected to fast-firing at 1120 °C using slow cooling gave the highest relative density (about 95 %) with fine grains microstructure and a d33 of 112 pC/N whereas that produced by conventional sintering resulted in d33 of 80 pC/N with a relative density of 88 % for the same dwell time (30 min). © 2024 The AuthorsArticle Citation - WoS: 9Citation - Scopus: 9Cold Sintering Assisted Two-Step Sintering of Potassium Sodium Niobate (knn) Ceramics(Elsevier, 2023) Karacasulu, Levent; Ahmetoğlu, Çekdar VakıfPotassium sodium niobate (KNN) ceramics were densified using a multiple-stage sintering process in which initially applied cold sintering process (CSP) was followed by the solid-state sintering between 1100 and 1120 °C. Comparative assessments demonstrated that multi-step sintered samples yielded better properties than conventionally sintering ones. The highest relative density (94.7%) and the best electrical properties were obtained from the sample subjected to cold sintering at 120 °C/1 h using 5 wt% deionized water subsequently heat-treated at 1120 °C/2 h, resulting in a monolithic KNN ceramic having a piezoelectric coefficient of 120 pC/N. © 2023 Elsevier B.V.Article 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.