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Yayın Düşük Sıcaklıkta Sinterlenen Piezoelektrik Seramiklerden İçi Boş Fiberlerin Üretimi, Aygıtların Tasarlanması Ve Uygulamaları(2016) Topaloğlu, Serkan; Doğan, Aydın; Menşur Alkoy, Ebru; Alkoy, SedatBu projenin amacı; piezoelektrik d31 modunda çalışan içi boş piezoseramik fiberleri temel alan ve aşağıda sıralanan dört temel aygıt uygulaması için içi boş fiberlerin alginate jelleşmesi ile üretimi ve potansiyel uygulamalar için bu mikro tüp yapısındaki fiberlerin elektromekaniksel performansını ortaya koymaktır. Ancak içi boş seramik fiberlerin üretimi güç ve problemlidir. Proje önerisi yöntem, tasarım, bileşim, uygulama açılarından literatürde hali hazırda kullanılan ve üzerinde çalışılan yöntemlerden farklı, bütünsel bir çözüm sunmaktadır. Projenin özgün noktaları sırasıyla; içi boş fiberlerin daldırma-kaplama ve alginate jelleşmesi yöntemiyle üretilecek olması, projede kurşun zirkonat titanatın (PZT) kurşun çinko niyobat (PZN) ve kurşun nikel niyobat (PNN) gibi piezoelektrikler ile yaptığı düşük sinterleme sıcaklığına sahip katı eriyiklerin incelenecek ve kullanılacak olması, içi boş fiberlerin iç yüzeylerinin elektrotlanmasının güçlüğü nedeniyle Ag esaslı elektrot tabakasının piezoseramik fiberlerin şekillendirilmesi esnasında elde edilmesi ve seramik ile birlikte pişirilmesidir. Proje çerçevesinde geliştirilmesi planlanan bu içi boş piezoseramik fiberler uygulama olarak mikroeyleyicilerde, içi boş fiberleri kullanarak hazırlanan piezokompozit yapılarla içi dolu fiberlere kıyasla bir mertebe daha düşük elektrik alan altında çalışan ve aktif titreşim kontrolü sağlayan aktif fiber kompozit uygulamalarında, denizdeki dalga ve gelgit hareketlerinden veya havada rüzgarın yarattığı düşük frekanslı hareketlerden enerji hasatıyla elektrik enerjisinin elde edilmesinde kullanılacak, esnek içi boş piezoseramik fiberleri temel alan serbest fiber dizinlerinde kullanılmışlardırYayın Effect of La substitution on the microstructure and dielectric properties of the sol-gel derived BaZr0.2Ti0.8O3 thin films(ELSEVIER SCIENCE SA, 2016) Mahmood, Asad; Mensur-Alkoy, Ebru; Naeem, Abdul; Iqbal, Yaseen; Ullah, Asad; Alkoy, SedatA-site deficient Ba1-xLa2x/3(Zr0.2Ti0.8)O-3 (BLZT) thin films with x = 0.00, 0.004, 0.006, 0.008, 0.02, 0.06 were processed using a sol-gel technique. X-ray diffraction analysis was used to investigate phase evolution of BLZT films with temperature. Scanning electron microscopy and atomic force microscopy were used to investigate the microstructure and surface topography of the fabricated BLZT thin films. The samples with x = 0.00-0.008 showed a homogeneous grain size distribution and uniform surface morphology; however, a certain degree of agglomeration was observed for the samples with x > 0.008 which increased with increasing La content. The magnitude of root mean square for the samples with x = 0.00, 0.004, 0.006, 0.008, 0.02 and 0.06 was recorded to be 3.53 nm, 3.06 nm, 2.32 nm, 2.02 nm, 3.36 nm and 4.71 nm, respectively. Relative permittivity (epsilon(r)) was observed to decrease with increasing temperature, and increased non-linearly with an increase in La content. Dielectric dispersion was observed for all the BLZT samples and er decreased with increasing frequency. (C) 2016 Elsevier B.V. All rights reserved.Yayın The effect of substrate and processing conditions on the properties of sol-gel derived Pb(Zr,Ti)O-3 thin films(INDERSCIENCE ENTERPRISES LTD, 2012) Alkoy, Ebru Mensur; Alkoy, Sedat; Shiosaki, TadashiLead zirconate titanate Pb(Zr0.45Ti0.55)O-3 PZT thin films were prepared by sol-gel method on Pt-(111)/Ti/SiO2/Si-(100) substrates from metal organic precursor solutions. Two different types of substrates were used in this study. It was concluded that the substrates were very effective on the structural and electrical properties of the films. The difference observed in the electrical properties of the films prepared on different substrates was explained by the difference in the crystallinity, (111) dominant orientation and grain size of the substrates. The films prepared at various temperatures from 650 degrees C down to 450 degrees C have all displayed full (111) orientation. The remnant polarisation of the PZT film fabricated at 650 degrees C was 42 mu C/cm(2) whereas remnant polarisation of the film annealed at 450 degrees C was > 15 mu C/cm(2) which was still high enough for practical applications.Yayın Electrical Properties and Impedance Spectroscopy of Lithium Modified Potassium Sodium Niobate Ceramics(TAYLOR & FRANCIS LTD, 2013) Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Alkoy, SedatLead-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.Yayın Electrical Properties and Impedance Spectroscopy of Modified Potassium Sodium Niobate Ceramics(IEEE, 2012) Alkoy, Ebru Mensur; Yavuz, Ayse Berksoy; Avdan, Duygu; Alkoy, SedatLead-free potassium sodium niobate (KNN) ceramics were prepared with lithium modification. Copper oxide was also added as sintering aid. Impedance spectroscopy was used as a tool to analyze electrical behavior of ceramics as a function of frequency from 100 Hz to 10 MHz at various temperatures.Yayın Fabrication of textured lead-free strontium barium niobate (SBN61) bulk ceramics and their electrical properties(ELSEVIER SCI LTD, 2016) Dursun, Sinan; Mensur-Alkoy, Ebru; Alkoy, SedatSr0.61Ba0.39Nb2O6 (SBN61) ceramic fibers with a high [001] texture were fabricated by a combination of alginate gelation method and templated grain growth process using acicular Ba2NaNb5O15 (BNN) template particles. The rod-like BNN template particles were prepared by molten salt synthesis method with salt/powder ratio of 2 giving the highest aspect ratio. Fibers were drawn from alginate based slurries without or with 10 wt% BNN template particles. Increasing sintering temperature and time were found to increase the texture. Textured SBN61 bulk ceramics with dimensions in cm scale were fabricated by wet packing a limited number of grain oriented green fibers and sintering the green bulk to obtain a dense, textured bulk ceramic through templated grain growth. A maximum texture fraction, f, of 0.91 was obtained, as measured by Lotgering factor. Increased remnant polarization and electromechanical properties were obtained as a result of this preferred grain orientation. (C) 2016 Elsevier Ltd. All rights reserved.Yayın 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, SedatIn 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.Yayın Kristalografik Dokuya Sahip Üstün Özellikli Piezoseramiklerin Ultrasonik Motor Uygulamaları(2016) Dursun, Sinan; Menşur Alkoy, Ebru; Yılmaz, Hüseyin; Alkoy, SedatLiteratürde dokulu piezoseramiklerin üzerine birçok özgün çalışma bulunmasına rağmen dokulu seramiklerin aygıt uygulaması literatürde ve uygulamada çok büyük eksiklik olarak göze çarpmaktadır. Bunun temel nedeni dokulu seramiklerin üretim yöntemlerinin yarattığı sınırlamalar nedeniyle bu seramiklerin ancak ince kesitlerde üretilebiliyor olmasıdır. Dolayısıyla ince kesitli seramiklerin kullanılabileceği özel uygulamalar dokulu seramiklerin kullanıma girmesine olanak verebilir. Doku kazandırılmış seramiklerin tek kristalleri ile yarışabilecek düzeyde özellik gösterdiği ve üretimi çok daha ucuz olduğundan dokulu seramikler ile üretilen ultrasonik motorların bilime, teknolojiye ve ekonomiye çok büyük faydalar sağlayacağı düşünülmektedir. Bu projede de, uluslararası bilimsel literatürdeki yukarıda belirtilen eksiklikler temel alınarak sırasıyla; i) Kübik ve altıgen prizma geometrisinde stator?e sahip ultrasonik motorlar sonlu elemanlar analizi ile tasarlanmış ve sert karakterdeki ticari PZT4 piezoseramikler ile tasarım doğrulanmıştır, ii) Ultrasonik motor uygulamasına uygun özelliklerde PMN-PZT esaslı bir piezoelektrik seramik bileşimi geliştirilmiştir, iii) Bu bileşimin dokulu olarak elde edilmesi için gerekli BaTiO3 esaslı tek kristal şablon parçacıklar 3 aşamalı bir ergiyik tuz yöntemiyle sentezlenmiştir, iv) Şablonlu tane büyütme ve şerit döküm yöntemleri ile PMN-PZT piezoelektrik seramik bileşimi dokulu olarak üretilmiştir, v) Elde edilen dokulu seramikler, optimize edilen USM tasarımında kullanılarak yeni nesil bir USM üretilmiştir, vi) Performans testleriyle bu USM?un muadillerinden daha üstün bir performans gösterdiği doğrulanmıştır.Yayın Macro and Microstructural Engineering of Piezoelectric Ceramics(TAYLOR & FRANCIS LTD, 2013) Alkoy, Sedat; Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Dursun, Sinan; Olukkent, Recep; Ozeren, YagizDimension, 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.Yayın Modified Lead-Free Potassium Sodium Niobate (KNN) and Their Properties(IEEE, 2012) Alkoy, Ebru Mensur; Yavuz, Ayse Berksoy; Alkoy, SedatIn this study, effects of lithium and tantalum modification on the structural and dielectric properties of potassium sodium niobate (KNN) ceramics were investigated. All ceramics were fabricated by pressureless sintering technique. Li, Li-Ta modifications were improved densification and thus dielectric properties. The dielectric properties of Li and Ta modified KNN ceramics were analyzed using AC impedance spectroscopy as a function of frequency from 100 Hz to 10 MHz in temperature range from 673 K to 798 K.Yayın 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, SedatRandom 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.Yayın Properties of [Pb(Zn1/3Nb2/3)O-3](x)-[Pb(Zr0.48Ti0.52)O-3]((1-x)) Ceramics With Low Sintering Temperature and Their 1-3 Piezocomposites(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016) Mensur-Alkoy, Ebru; Kaya, Mustafa Yunus; Avdan, Duygu; Alkoy, SedatIn this paper, dense (x)PZN-(1 - x)PZT ceramics were prepared at sintering temperatures as low as 950 degrees C with PZN ratios of x = 0.4, 0.5, and 0.6. The 0.4PZN-0.6PZT composition was found to crystallize in the perovskite phase at this sintering temperature without the presence of any other secondary phases. Higher electrical and electromechanical properties were obtained from the 0.4PZN-0.6PZT composition compared with the x = 0.5 and x = 0.6 counterparts. Dielectric constant, piezoelectric charge coefficient, electromechanical coupling coefficient, and mechanical quality factor of 0.4PZN-0.6PZT were found to be 2608, 477 pC/N, 64.4, and 65, respectively. While the Curie temperature was 140 degrees C for pure PZN, the Curie temperature was measured as 300 degrees C for x = 0.4 composition. Green PZN-PZT fibers with circular cross section were drawn using alginate gelation method from the 0.4PZN-0.6PZT composition. Dense fibers were obtained after the sintering process, and piezocomposites were prepared with 1-3 connectivity using fibers with an average diameter of 600 mu m. Composites with volume fraction of 20 vol% were investigated for passive acoustic sensor applications. Electrical properties of piezocomposites were found to be scalable and compatible with the electrical properties of the bulk composition. The dielectric constant, piezoelectric charge coefficient, and maximum strain value of the PZN-PZT 1-3 piezocomposite were measured as 345, 165 pC/N, and 0.13%, respectively.Yayın Sodium niobate particles with controlled morphology synthesized by hydrothermal method and their use as templates in KNN fibers(ELSEVIER SCIENCE BV, 2014) Ozeren, Yagiz; Mensur-Alkoy, Ebru; Alkoy, SedatSodium niobate - NN (NaNbO3) powders were synthesized by hydrothermal process to be used as template particles in the fabrication of textured lead free piezoelectric ceramics. Sodium hexaniobate-Na8Nb6O19 center dot 13H(2)O particles with rod-like morphology were synthesized at 120 degrees C. Particles with needle-like morphology and Na-2(Nb2O6)(H2O) phase started to form at temperatures of 130 degrees C and above. Synthesis at 150 degrees C yields particles with totally needle-like morphology and consisting entirely of the Na-2(Nb2O6)(H2O) phase. Sodium niobate-NaNbO3 particles with cubic morphology were synthesized at temperatures of 160 degrees C and above. Rod-like and needle-like morphology was retained even after annealing at 400 degrees C for 1 h. A preliminary study was also done to integrate these anisometric template particles in the preparation of textured potassium sodium niobate (KNN) fibers. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
