Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Ferroelectric to Relaxor Crossover in Zr-Doped BaTiO3-Based Ceramics and Its Consequences for the Electrocaloric Effect(Royal Soc Chemistry, 2025) Akkasoglu, Oguz; Karakaya, Merve; Novak, Nikola; Fulanovic, Lovro; Adem, UmutNa0.5Bi0.5TiO3 (NBT)-substituted BaTiO3 (BT)-rich solid solutions demonstrate significant electrocaloric effects owing to the first-order nature of their ferroelectric phase transition. However, their narrow phase transition range and relatively high transition temperature limit their suitability for electrocaloric cooling applications. To address these issues, we have investigated the impact of Zr-substitution (0-5 mol%) at the B-site on the phase transition behaviour of 0.7BT-0.3NBT solid solution. Our findings indicate that Zr-substitution strongly decreases the tetragonality and the Curie temperature of the samples. All samples exhibit relaxor-like characteristics, following the Vogel-Fulcher approach. However, at low Zr doping (0-3 mol%), a spontaneous transition into the ferroelectric phase is also observed on cooling from high temperatures. At higher Zr doping (4-5 mol%), the transition into the ferroelectric phase disappears and the sample presents canonical relaxor behaviour. The samples with canonical relaxor behaviour (4-5 mol% Zr) feature wider temperature ranges where a significant electrocaloric response is sustained, which yielded a large Tspan of similar to 45 degrees C for the 4% Zr-doped sample where a Delta T value of 0.77 K was maintained.Article Citation - WoS: 2Citation - Scopus: 2Stabilization of the First-Order Phase Transition Character and Enhancement of the Electrocaloric Effect by Na<sub>0.5</Sub>bi<sub>0.5< Substitution in Batio<sub>3</Sub> Ceramics(Royal Soc Chemistry, 2024) Karakaya, Merve; Gurbuz, Irem; Fulanovic, Lovro; Adem, UmutThe electrocaloric properties of BaTiO3-based Pb-free ferroelectric materials are widely investigated. One approach to achieving a large electrocaloric response is making use of the substantial polarization change associated with the first-order phase transition at the Curie temperature. To make use of this approach, we have investigated the electrocaloric response of (1 - x)BaTiO3-xNa0.5Bi0.5TiO3 (BT-NBT) ceramics for x = 0.05, 0.10, 0.20 and 0.30. For this BT-rich part of the solid solution, it is established that increasing the NBT content increases the tetragonality of the BaTiO3. We show that this increase in tetragonality with NBT substitution helps to maintain the first-order nature of the phase transition in BaTiO3 and correspondingly a large electrocaloric response, despite the simultaneous enhancement of relaxor ferroelectric character with the NBT substitution. A significantly larger effective electrocaloric temperature change (Delta Teff) of 1.65 K was obtained for the x = 0.20 sample under 40 kV cm-1, using the direct measurement of the electrocaloric effect, which is in reasonable agreement with the indirect measurements.