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    Electrical Properties and Impedance Spectroscopy of Lithium Modified Potassium Sodium Niobate Ceramics
    (TAYLOR & FRANCIS LTD, 2013) Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Alkoy, Sedat
    Lead-free potassium sodium niobate (KNN) ceramics were prepared with lithium and tantalum modification. Structural properties were investigated. Impedance spectroscopy was used as a tool to analyze electrical behavior of ceramics as a function of frequency from 100Hz to 10MHz at a temperature range from 573K to 798K. Neither Li nor Li + Ta modification caused any secondary grain boundary phase, however both of them caused a densification of the ceramic. Increasing the lithium addition was found to decrease the impedance, while the Li + Ta addition drastically increased it. Finally, a temperature induced relaxation process was observed in the samples with the relaxation frequency shifting with temperature.
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    Electrical Properties and Impedance Spectroscopy of Pure and Copper-Oxide-Added Potassium Sodium Niobate Ceramics
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012) Alkoy, Ebru Mensur; Berksoy-Yavuz, Ayse
    Pure and 1 mol% CuO-added lead-free potassium sodium niobate K0.5Na0.5NbO3 (KNN) ceramics were prepared by the conventional solid-state calcination method. Copper oxide was mainly used as a sintering aid in the KNN structure. Microstructural analyses clearly showed that the CuO formed a secondary phase at the grain boundaries. Impedance spectroscopy was used as a tool to analyze the electrical behavior of KNN ceramics as a function of frequency from 100 Hz to 10 MHz at various temperatures. The impedance studies proved that CuO led to the formation of a secondary grain boundary phase, as well as creation of highly mobile point defects. The relaxation time of copper-added samples was less than that of pure KNN. This shorter time indicated a higher space charge mobility for CuO-added samples. The thermal activation energy for relaxation of charge carriers (E-g) was calculated as 0.73 eV for CuO-added samples.
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    Growth of NBT template particles through topochemical microcrystal conversion and their structural characterization
    (WILEY, 2017) Dursun, Sinan; Mensur-Alkoy, Ebru; Sabuncu, Abdulsamet; Berksoy-Yavuz, Ayse; Gulgun, Mehmet Ali; Alkoy, Sedat
    In this study, uniform rectangular plate-like perovskite Na0.5Bi0.5TiO3 templates were obtained by molten salt synthesis method in three steps. Perovskite plate-like Na0.5Bi0.5TiO3 templates were synthesized from bismuth-layered Na0.5Bi4.5Ti4O15 by topochemical microcrystal conversion method at the third and final step. The most important point was that the plate-like morphology remained as desired, but templates were obtained in cubic perovskite structure. The Na2CO3 excess in the third step was the main controlling parameter. The crystalline orientation of the particles was investigated by electron backscatter diffraction analysis. The results indicated that the particles are single crystalline in nature. In the case of the 90mol% excess of the stoichiometric Na2CO3 ratio, the NBT platelets had highly regular, rectangular prismatic morphology and single-crystal nature. The structure was also confirmed through high-resolution transmission electron microscope and selected area electron diffraction analysis.
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    Macro and Microstructural Engineering of Piezoelectric Ceramics
    (TAYLOR & FRANCIS LTD, 2013) Alkoy, Sedat; Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Dursun, Sinan; Olukkent, Recep; Ozeren, Yagiz
    Dimension, shape and materials' properties are the most basic characteristics of a piezoelectric ceramic transducer determining the device performance. In our studies better electromechanical performance was obtained from piezoelectric ceramic itself by creating designs based on built-in amplification mechanisms obtained through the shape and geometry of the transducer, i.e. the macroscale engineering. Piezoceramics in thin hollow shell and fiber forms were fabricated by slip casting and alginate gelation. Additionally, improving materials properties along preferred directions can be achieved through the fabrication of crystallographically textured piezoceramics, i.e. Microscale Engineering. Alginate gelation and templated grain growth was used to produce them.
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    Processing and Properties of Textured Potassium Sodium Niobate [K,Na]NbO3 Ceramic Ribbons by Alginate Gelation Method
    (WILEY-BLACKWELL, 2014) Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Alkoy, Sedat
    Random and < 001 > textured potassium sodium niobate - [K,Na]NbO3 (KNN) ceramics with 1 mole% CuO sintering aid were fabricated in ribbon form through a combination of novel alginate gelation process and templated grain growth methods using platelike sodium niobate - NaNbO3 (NN) template particles. The platelike NN template particles were prepared by a two-step molten salt synthesis method. Ribbons were drawn from alginate-based slurries without or with 10 wt% NN template particles using 50mm long slit nozzle with a rectangular orifice of 10mmx1mm. Development of crystallographic texture as a result of varying sintering time and temperature was evaluated through the calculation of the degree of orientation as measured by the Lotgering factor (integral((001))) and an integral((001)) of 0.81 was achieved. The electrical properties of textured ribbons were evaluated with polarization and strain versus electric field measurements.