Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4719

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Author: search.filters.author.Adem, UmutPublisher: search.filters.publisher.Elsevier Ltd.

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Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 13
    Citation - Scopus: 16
    Electrocaloric 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, Umut
    We 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: 33
    Citation - Scopus: 33
    Influence of Aging on Electrocaloric Effect in Li+ Doped Batio3 Ceramics
    (Elsevier Ltd., 2019) Güvenç, Çetin Meriç; Adem, Umut
    Aging 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.
  • Article
    Multiferroic Materials: Physics and Properties
    (Elsevier Ltd., 2016) Buurma, A. J. C.; Blake, G. R.; Palstra, T. T. M.; Adem, Umut
    Multiferroics are materials in which magnetism and ferroelectricity coexist. They are of fundamental interest to understand electronic behavior coupling magnetic interactions and electric dipolar order. Moreover, they are of applied interest because they allow various types of novel magnetic and electric device structures. We distinguish two important classes of multiferroic materials and discuss mechanisms and materials belonging to each class separately. In the first group of multiferroics, magnetization and polarization arise independently from each other. In the second category of multiferroics, ferroelectricity is induced by magnetic order, resulting in strong magnetoelectric coupling. We also briefly discuss multiferroic thin film heterostructures showing interfacial magnetoelectric coupling interactions with potential applications in memory devices.