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: 6Citation - Scopus: 6Electrocaloric Effect of Alkali Co-Substituted Sr0.6ba0.4nb2o6 Ceramics(Elsevier Ltd., 2020) Kurnia, Arif; Emriadi; Mufti, Nandang; Zulhadjri; Adem, UmutWe have investigated the electrocaloric properties of K+ and Na+ co-substituted Sr0.6Ba0.4Nb2O6 (SBN) ceramics using the indirect method. Tetragonal tungsten bronze (K0.5Na0.5)2x(Sr0.6Ba0.4)5-xNb10O30 (KNSBN) with x = 0.24 was synthesized using dual-step sintering. Despite the low amount, K+ and Na+ co-substitution resulted in normal ferroelectric behaviour, showing no significant shift in the dielectric maximum temperature of 111 °C with increasing frequency. Maximum electrocaloric temperature change (?T) of 0.3 K was observed at an electric field of 30 kV/cm (?E) yielding the largest electrocaloric responsivity (?T/?E) among SBN based ceramics. This relatively large value is in agreement with the larger pyroelectric coefficient of KNSBN compared to SBN based ceramics. © 2020 Elsevier B.V.Article Citation - WoS: 13Citation - Scopus: 16Electrocaloric Properties of Ba0. 8sr0. 2ti1-Xzrxo3 (0? X? 0.1) System: the Balance Between the Nature of the Phase Transition and Phase Coexistence(Elsevier Ltd., 2020) Şanlı, Keriman; Adem, UmutWe investigate the electrocaloric effect of Ba0.8Sr0.2Ti1-xZrxO3 (0 ≤ x ≤ 0.1) system by comparing the electrocaloric temperature change (ΔT) of different compositions belonging to the different regions of the phase diagram. We show that as the amount of Zr increases, electrocaloric temperature change initially decreases as the phase transition gets diffuse then increases again as the composition of the samples are located closer to the critical point where different ferroelectric phases coexist. Since the critical point is reached at relatively low Zr substitution levels (i.e. around x = 0.07), the phase transition doesn't get too diffuse and thefore the compositions between x = 0 and x = 0.10 (which contains higher Zr than the critical point composition) have comparable ΔT values. Electrocaloric efficiency of these compositions (x = 0.03, 0.05 and 0.07) is around 0.20 K mm/kV at 20 kV/cm. We discuss the results in terms of the balance between the nature of the phase transition and proximity to the critical point, based on the phase diagram.Article Citation - WoS: 33Citation - Scopus: 33Influence of Aging on Electrocaloric Effect in Li+ Doped Batio3 Ceramics(Elsevier Ltd., 2019) Güvenç, Çetin Meriç; Adem, UmutAging creates significant changes in the properties of the ferroelectric materials such as dielectric and piezoelectric properties. However, the influence of aging on the electrocaloric effect (ECE) has not yet been investigated. In this work, we investigate the effect of the aging on the ECE in acceptor (Liþ) doped BaTiO3 ceramics. We observe that aging induced defect polarization (PD) reduces the saturation polarization of the doped samples until Tc ¼ 115 C. Above that temperature PD loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below TC due to aging effect results in a sharper slope change in the temperature dependence of electrical polarization in aged samples which causes an increase in the electrocaloric temperature change of Liþ doped BaTiO3 ceramics up to 23% at TC. Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample.