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Gebze, Turkey

Mensur-Alkoy E.,Maltepe University | Berksoy-Yavuz A.,Gebze Institute of Technology | Alkoy S.,Gebze Institute of Technology | Alkoy S.,ENS Piezodevices Ltd.
Journal of the American Ceramic Society | Year: 2014

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 50 mm long slit nozzle with a rectangular orifice of 10 mm x 1 mm. 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 (f(001)) and an f(001) of 0.81 was achieved. The electrical properties of textured ribbons were evaluated with polarization and strain versus electric field measurements. © 2014 The American Ceramic Society. Source

Dursun S.,Kocaeli University | Mensur-Alkoy E.,Maltepe University | Alkoy S.,Kocaeli University | Alkoy S.,ENS Piezodevices Ltd.
Journal of the European Ceramic Society | Year: 2016

Sr0.61Ba0.39Nb2O6 (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 10wt% 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. © 2016 Elsevier Ltd. Source

Ozeren Y.,Gebze Institute of Technology | Mensur-Alkoy E.,Maltepe University | Alkoy S.,Gebze Institute of Technology | Alkoy S.,ENS Piezodevices Ltd.
Advanced Powder Technology | Year: 2014

Sodium 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-Na8Nb6O19·13H2O particles with rod-like morphology were synthesized at 120 °C. Particles with needle-like morphology and Na2(Nb2O6)(H2O) phase started to form at temperatures of 130 °C and above. Synthesis at 150 °C yields particles with totally needle-like morphology and consisting entirely of the Na2(Nb2O6)(H2O) phase. Sodium niobate-NaNbO3 particles with cubic morphology were synthesized at temperatures of 160 °C and above. Rod-like and needle-like morphology was retained even after annealing at 400 °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. © 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. Source

Mensur-Alkoy E.,Maltepe University | Kaya M.Y.,Gebze Technical University | Avdan D.,Gebze Technical University | Alkoy S.,Gebze Technical University | Alkoy S.,ENS Piezodevices Ltd.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2016

In this paper, dense (x)PZN-(1-x)PZT ceramics were prepared at sintering temperatures as low as 950 °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 °C for pure PZN, the Curie temperature was measured as 300 °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 \text{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. © 2016 IEEE. Source

Alkoy S.,Gebze Institute of Technology | Alkoy S.,ENS Piezodevices Ltd. | Mensur-Alkoy E.,Maltepe University | Berksoy-Yavuz A.,Gebze Institute of Technology | And 4 more authors.
Ferroelectrics | Year: 2013

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. © 2013 Copyright Taylor and Francis Group, LLC. Source

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