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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 Electric Field-Induced Strain Behavior in Lithium- and Copper-Added Potassium Sodium Niobate Piezoceramics and 1-3 Piezocomposites(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011) Alkoy, Ebru Mensur; Berksoy, Ayse; Tekdas, A. SerkanPotassium sodium niobate (KNN)-based lead-free materials were prepared and their field-induced strain behaviors were investigated. Ceramic lead-free piezoelectric materials were prepared in bulk and fiber forms with 1 mol% CuO-added potassium sodium niobate K(0.5)Na(0.5)NbO(3) and x = 7 mol% lithium-modified (K(0.5-x/2) Na(0.5-x/2)Li(x))NbO(3) compositions. Fibers were drawn using a novel alginate gelation technique. Piezocomposites were prepared from these fibers with 1-3 connectivity and an epoxy matrix. A fully recoverable electrostrain of up to approximately 0.11% was observed in the CuO-added sample, whereas the Li-modified sample yielded up to 0.10% at 50 kV/cm electric field. A strain value of up to approximately 0.03% at 50 kV/cm electric field was obtained for piezocomposites prepared from lithium-modified fibers. The high-field converse piezoelectric coefficient was calculated from the strain-electric field (x-E) graph for all samples. Strain characteristics of the bulk and piezocomposite samples were analyzed based on the variation of strain with respect to square of the polarization (x-P(2)) to determine the electrostrictive contribution to the strain.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 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, AysePure 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.Yayın Electrical Properties of 1-3 Piezocomposites with Potassium Sodium Niobate Fibers(TAYLOR & FRANCIS LTD, 2011) Alkoy, Ebru Mensur; Tekdas, A. Serkan; Berksoy, AyseLead-free 1 mole% CuO-added potassium sodium niobate K0.5Na0.5NbO3 (KNN) fibers were drawn using a novel alginate gelation technique. Piezocomposites with 1-3 connectivity were prepared with an epoxy matrix with various fiber volume fractions (V-f). The dielectric constant of the piezocomposites were found to increase from 67 to 190 with the addition of CuO into KNN and increasing Vf in the 1-3 piezocomposite. A fully recoverable electrostrain of 0.023% for the piezocomposites with V-f = 0.63 under an electric field of 4 kV/mm. A very high electrostrictive Q(33) coefficient of 162x10(-3) m(4)/C-2 was obtained from piezocomposites.Yayın Field-induced recoverable strain behavior of CuO-added K0.5Na0.5NbO3 ceramics and 1-3 fiber/epoxy piezocomposites(AMER INST PHYSICS, 2010) Alkoy, Ebru MensurLead-free, dense, 1 mol % CuO-added potassium sodium niobate K0.5Na0.5NbO3 (KNN) fibers were successfully drawn using a novel alginate gelation technique. Piezocomposites with 1-3 connectivity were prepared with an epoxy matrix with various fiber volume fractions (V-f). Electrical properties of the piezocomposites were investigated and compared with bulk KNN ceramics of the same composition. The dielectric constant of the piezocomposites were found to increase from 67 to 191 with the addition of CuO into KNN and increasing V-f in the piezocomposite. A constricted, antiferroelectriclike double hysteresis polarization versus electric field (P-E) loop was observed in bulk KNN. A large and fully recoverable electrostrain of 0.07% was measured for bulk KNN and 0.03% for the piezocomposites under an electric field of 50 kV/cm, respectively. The double hysteresis P-E loop and the recoverable nature of the electrostrain was due to the Cu'''(Nb)-V-O(center dot center dot) defect dipoles creating an internal field that restores the original domain pattern when the field is removed. A very high electrostrictive Q(33) coefficient of 35.6 X 10(-3) m(4)/C-2 and an even higher Q(33) of 162 X 10(-3) m(4)/C-2 was obtained for bulk KNN and piezocomposites, respectively. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3503845]Yayın Microstructural features and electrical properties of copper oxide added potassium sodium niobate ceramics(ELSEVIER SCI LTD, 2010) Alkoy, Ebru Mensur; Papila, MelihIn this study, effects of 0.5, 1.0 and 1.5 mole% CuO addition on the properties of potassium sodium niobate (K0.5Na0.5)NbO3-KNN ceramics were investigated. Pure KNN and CuO-added KNN pellet samples were sintered at 1100 and 1090 degrees C for 4 h, respectively. Phase analysis showed that all samples crystallized in pure orthorhombic perovskite phase. Addition of 1.0 and 1.5 mole% CuO caused grain growth, densification and formation of a liquid phase at the grain boundaries. Curie temperature has shifted from 480 to 435 degrees C with increasing CuO ratio. The most remarkable characteristic of the hysteresis loops were the constricted nature of the 0.5 mole% CuO-added KNN's curve and the antiferroelectric-like appearance of the 1.5 mole% CuO-added KNN's curve. Piezeoelectric properties of d(33) = 120 pC/N, k(p) = 0.27 and Q(m) = 772 were obtained from the 1.5 mole% CuO-added KNN. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.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.
