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Thesis
Here you will find information about the PhD, MSc and BSc thesis to come out of the Piezodevices Research Group. We’ve had many wonderful lab members be involved in a variety of different projects since we first started back in 2002, and are proud to showcase their hard work with the list of PhD, MSc thesis below.
PhD Thesis
Here you will find information about the PhD thesis which are completed by the Piezo Devices Research Group' Doctorate Students. There are 4 PhD theses completed.
NAMIK KEMAL GÖZÜAÇIK, 2023
Investigation of antiferroelectric ceramics for high energy density capacitor and electrocaloric applications
Lanthanum doped lead zirconate titanate (PLZT) ceramics with superior properties are very popular for piezoelectric and electro-optical applications and are widely used in smart sensors and optical processing devices. Antiferroelectric ceramic materials such as PLZT and lanthanum doped lead zirconate stannate titanate (PLZST), which also exhibit electric field-induced phase transition and composition-controllable electrical properties, are widely used in high-power energy storage device applications and cooling devices. Due to their high piezoelectric and ferroelectric properties, bismuth sodium titanate (BNT)-based piezoelectric ceramics have been investigated as an alternative to lead-based piezoelectric ceramics. Bismuth sodium titanate-bismuth potassium titanate-barium titanate (BNT-BKT-BT) ternary ceramic system stands out more in energy storage applications due to its high piezoelectricity, depolarization/Curie temperature and low remnant polarization compared to other BNT-based ceramics such as BNT-BT or BNT-BKT. In this thesis, different ratios of lanthanum doped PLZT and different rare earth elements doped BNT-BKT-BT (BNKBT) ceramics were fabricated by solid-state reaction method, and investigated for high energy density capacitor and electrocaloric applications by carrying out structural and electrical characterizations. In PLZT ceramics, the relaxor ferroelectric character became dominant with 8 mol% La doping. Rare earth element doping has been quite successful in increasing the releasable energy density (Wre) for high energy density capacitor applications in BNKBT ceramics. Five times higher Wre was obtained in 1 mol% Nd doped ceramic, when compared to undoped ceramic. The highest electric field-induced strain levels were measured as 0.58% and 0.35% at 65 kV/cm for 0.5 mol% Gd and 1 mol% Ce doped BNKBT ceramics, respectively. The highest releasable energy densities were calculated as 0.64 J/cm3 and 0.54 J/cm3 at 65 kV/cm for 1 mol% Nd and 1 mol% Ce doped BNKBT ceramics, respectively. The highest electrocaloric temperature change (ΔTmax) was calculated as 1.15 K at 60 kV/cm for 8 mol% La doped PLZT ceramic.
AYŞE BERKSOY YAVUZ, 2018
Fabrication, characterization and energy harvesting application of crystalografic textured [Pb(Mg1/3Nb2/3)O3]- [PbTiO3] ceramics
In recent years, energy harvesting devices have become a popular field of research especially in wireless sensor networks, wearable products, military or civilian mobile and wireless electronic devices (with high power input at low frequencies). Recent developments in wireless sensors and micro-electro-mechanical systems (MEMS) indicate that energy harvesters can become an alternative to traditional batteries. Since piezoelectric materials convert mechanical energy into electrical signals, they gain importance for powering the wireless sensor systems (RF-ID) when they are integrated into energy harvesters. In recent years, ceramics fabricated with a crystallographic texture by preferentially orienting the grains in certain orientations, have attracted attention due to their superior properties that can compete with single crystals and commercial lead zirconate titanate (Pb(Zr,Ti)O3 -PZT) without requiring an expensive infrastructure . In addition, using templated grain growth and tape casting methods, textured ceramics with millimeter thickness can be successfully produced. In this thesis; 0,675Pb(Mg1/3Nb2/3)O3-0,325PbTiO3 (referred to as PMN-PT) piezoceramics, which was a lead-based solid solution with improved electrical properties, will be fabricated in thin plate form, and then energy harvesting designs was be realized.
MUSTAFA YUNUS KAYA, 2018
Design, fabrication, characterization and applications of flextensional transducer
Transducers are devices that convert an energy form into another form of energy. Electroacoustic transducers are used in underwater acoustic applications and the most commonly used type is piezoelectric transducers. When a piezoelectric transducer needs to be operated at frequencies less than 100 kHz, it is possible that the transducer will produce a desired acoustic output power only with very high deformation. Since the maximum displacement in the piezoceramic materials is in the range of 0.1-0.2%, it is necessary to create rational designs that amplifies displacement level. Flextensional transducers is one of these designs and it consists of a piezoelectric ceramic as main drive element with a metal shell and is divided into 7 sub classes. In this thesis, novel and unique class V type flextensional transducer was developed using ATILA finite element analysis (FEA) software.
SİNAN DURSUN, 2017
Ultrasonic motor applications of crystalographically textured piezoceramics
The aim of this study is piezoelectric ceramics that produced with crystallographic textured with superior properties for use the application of an ultrasonic motor (USM) which designed by finite element analysis and to make basic measurements of the produced prototip devices. The production of ceramics were carried out with two basic approaches in order to used the ceramics in USM application which have both hard and soft piezoelectric properties. It was achieved to the selected piezoelectric ceramics have hard and soft combinatory by crystallographic orientation and an appropriate dopant addition. This thesis study was established five main sections which each of these sections include specific purpose to improvement study and results.
MSc Thesis
Here you will find information about the MSc thesis which are completed by the Piezo Devices Research Group' Master Students. There are 33 master theses completed.
Preparation of PZT and PLZT thin films on different substrates by sol-gel spin coating methods and investigation of their properties
MUSTAFA ÇAĞRI BAYIR, 2019
Piezoelectric and electrooptic materials have been used and researched for a long time. Thin film form of these materials possesses higher properties compared to its bulk form and especially lead-based systems are more preferred despite its toxicity. The aim of this study is to prepare the Lead Zirconate Titanate (PZT) and Lead Lanthanum Zirconate Titanate (PLZT) thin films with different compositions on different substrates by using sol-gel spin coating technique to determine the effect of these parameters on the material properties. In this study, PZT compositions were prepared with the specific amount of excess lead and, the films were annealed at various temperatures to obtain the pure perovskite phase.
Preparation and characterization of microstructurally engineered textured 0.9PMN-0.1PT piezoelectric ceramics
YUSUF KILIÇ, 2019
Lead-based piezoelectric materials are known with their high electrical and electromechanical properties for potential applications. Among various lead-based piezoelectric materials, (1-x)Pb(Mg1/2Nb2/3)O3–(x)PbTiO3 ceramics (abbreviated as PMN-PT) are promising materials for transducers, medical ultrasound, ultrasonic motors and actuators. In this study, 0.9PMN-0.1PT was chosen due to relaxor ferroelectric response of this composition. Piezoelectric ceramic powders were synthesized by solid-state reaction route. The final PMN-PT particle size of the powders was measured as 0.18 µm. The samples of 0.9PMN-0.1PT were prepared with two methods as dry-pressing and tape-casting. Moreover, barium titanate (BaTiO3) template particles were synthesized by molten salt synthesis method and were used to texture the 0.9PMN-0.1PT with ratio of 5%-vol. A combination of tape-casting and template grain growth was used to obtain textured PMN-PT samples. All samples were sintered at 1150oC for various durations. Microstructural and compositional analyses have been carried out using scanning electron microscope (SEM) and X-ray diffraction (XRD). Dielectric and ferroelectric properties have been investigated. Pure perovskite structure was obtained in all sintered samples. Temperature-depended measurement of dielectric constant was performed. Electric field-induced strain was measured as ~0.14% at 30 kV/cm. The Curie temperatures were measured at 1 kHz, 10 kHz and 100 kHz as 41C, 43C and 45C for dry-pressing samples and 39C, 41C and 43C for textured samples, respectively, indicating the relaxor nature of the ceramics. Remnant polarization (Pr) of non-textured sample was measured as ~2Pr =12.7 µC/cm2 at 30 kV/cm and was also measured as 6.4 µC/cm2 at 30 kV/cm for the textured sample.
Fabrication of antiferroelectric PZSnT bulk ceramics
HÜSEYİN ALPTEKİN SARI, 2019
Antiferroelectric ceramics that are being used in many areas today such as high energy density capacitors, electromechanical systems. Due to their structures, they do not preserve the permanent polarization and keep transitioning between ferroelectric and antiferroelectric states under application of electric field unlike the ferroelectric counterparts. Whenever the electric field is removed, they return back to the original state. PZSnT ceramics are widely well-known antiferroelectric ones. Generally antiferroelectric ceramics are fabricated by thin film or Sol-Gel methods. In this work, antiferroelectric PZSnT ceramics were produced by utilizing the traditional solid state calcination method via using oxide powders. After the application of the binder process to the synthesized intrinsic and extrinsic PzSnT powders, the ceramics were molded by single axis pressing and condensed for 2 hours at 1275°C
Investigation of electrical properties of Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PNN-PZT) ceramics and their device application
MEHMET GÜRKAN ÖZYAZICI,2018
Underwater SONAR (Sound Navigation And Ranging) systems, medical imaging systems etc. use piezoelectric ceramics materials. Lead Zirconate Titanate(PZT) is the most commercially used polycrystalline piezoelectric composition because of its relatively higher properties and higher Curie temperature, utilizing in a wide range of applications. In this study, the objective was to investigate relatively new polycrystalline piezoelectric materials used in some certain applications such as passive underwater listening, ultrasonic imaging. Some compositions in the literature were investigated in order to enhance the properties of the PZT ceramic. Lead Nickel Niobate (abbreviated as PNN) is one of the first known polycrystalline compositions as relaxor ferroelectric. In this study, producibility of PNN-PZT with advanced electrical properties was investigated in order to improve aforementioned device applications. However, bulk piezoceramics have low efficiency in underwater applications. As a result, piezocomposites with 1- 3 connectivity was fabricated. Ceramic fibers were fabricated by alginate gelation route. 1-3 piezocomposites were manufactured from those ceramic fibers. It was aimed to the superior electromechanical properties PNN-PZT composition for these applications, manufacturing of its fibers with alginate gelation route and fabrication of 1-3 piezocomposites from those fibers for the first time. Two different fabrication methods (Mixed Oxide Route and Columbite Precursor Route) were investigated and X-ray diffraction results, SEM images, and electrical measurements were conducted for both routes comparably. Modelling by Finite Element Method of PNN-PZT composition were also investigated in this study. Hollow spherical hydrophones were also fabricated as a final device demonstration.
Design and fabrication of a mini tonpilz transducer from piezoelectric textured ceramics
KADİR KOÇAK, 2018
In this thesis study 0.4Pb(Mg1/3Nb2/3)-0.25PbZrO3-0.35PbTiO3 (PMN PZT) composition had been synthesized, tape casting was carried out for textured ceramic production with the addition of barium titanate-BaTiO3 (BT) plate template. Barium titanate-BaTiO3 (BT) templates were oriented by the tape casting process. The tapes were dried after the casting then they were cut into ring shape with the desired dimensions. After the cutting, tapes were kept under 60 ̊C for 30 minutes, then joined together by uniaxial press and densified by isostatic press before and after the binder removal process. Same process was carried out for the randomly oriented ceramics as well. In this thesis study commercial PZT5A powder was used for comparison. After production, the ceramics that were produced with the same size were electrically characterized. The aluminium and steel blocks with the sizes determined by the finite elements method were processed with CNC. Two ceramics were used for each mini-tonpilz. Two devices were fabricated out of every composition. Finally, devices were electrically characterized after they were coated with polyurathane. Electrical characterizations were performed; before polyurathane coating, after polyurathane coating and finally underwater measurement.
Development of crystallgraphically textured PMN-PZT piezo-ceramics for bender type transducer applications
MUSTAFA ÜNSAL ÜNVER, 2018
The purpose of this thesis is to synthesize textured ceramics which exhibit superior properties by providing both hard and soft character properties for the selected prototype 0.40Pb(Mg1/3Nb2/3)O3-0.25PbZrO3-0.35PbTiO3 PMN-PZT composition and comparing these synthesized ceramics with commercial PZT4 for bender type transducer applications. The hard characteristic properties was obtained by doping with MnO2 to the ceramic system. The soft characteristic was obtained by gaining crystallographic texture by adding template particles to the system. The electrical and electromechanical characterization of the synthesized textured ceramics was carried out. Synthesized textured ceramics has shown properties comparable to the commercial PZT4. Finally, frequency-admittance measurements of bender type transducers made from synthesized textured ceramics and commercial PZT4 ceramics were carried out.
Structural and electrical characterization and improvement of low temperature sintering piezoelectric ceramic compositions
DUYGU AVDAN, 2017
Lead Zinc Niobate Pb(Zn1/3Nb2/3)O3-(PZN) is a piezoelectric material with low sintering temperature, however, in polycrystalline form it usually contains pyrocholore phase which negatively affects the electrical properties. Therefore PZN has been alloyed with certain amount of perovskite stabilizers; such as Lead Zirconium Titanate Pb(ZryTi1-y)O3-(PZT) to form solid solution to be formulated as wt.1%PbO added Pb[(Zn1/3Nb2/3)x(Zry Ti1-y)1-x]O3] in order to obtain a pyrocholore-free perovskite phase. In this study PZN was stabilized with PZT in the [xPbZn1/3Nb2/3-(1- x)PbZr0.48Ti0.52- O3] composition where x=0.1-0.6. PZN-PZT powders were synthesized by the solid state calcination method. Calcination temperature ranged from 825ºC to 855ºC for 4 hours in close alumina crucibles. X-ray diffraction (XRD) results were pointed out that x=0.4 ceramic powder calcined at 850ºC - 4 hours was sufficient to obtain PZN-PZT at pure perovskite phase. After calcination process, ceramic pellets were prepared with die press and densification behavior is observed during sintering at 860-950ºC for 4 hours in double alumina crucibles. Ceramics that were sintered at 950ºC - 4 hours,have the relative density of >95%, Curie temperature (Tc) of these specimens was 287ºC and piezoelectric constant (d33) was measured as 465 pC/N.
Production and electrical characterization of based on (K,Na)NbO3 1-3 piezo-composites
MUZAFFER VARDARLI, 2015
In this thesis, to ensure the manufacturability of KNN based 1-3 piezocomposite are required. In addition, it is aimed to achieve the desired electrical value for the hydrophone and transducer applications in the produced composites. Typically, studies have been made in the literature containing lead Pb(Zr,Ti)O3 composites are based on the compounds. In this thesis, environment friendly lead-free KNN/epoxy composite manufacturing technology will provide a different approach.
Fabrication of hemisphere shaped piezoelectric transducers using slip casting method and electrical characterizations
RECEP OLUKKENT, 2013
In this thesis, the fabrication, characterization and design of thin-shell hemisphere piezoelectric ceramic tranducers were carried out. Transducers were fabricated using slip casting methods and characterized through microstructural examinations and electrical measurements. In this study, two different types of powders BM500 and BM400 provided by Sensor Tech and PZT4, PZT-5A, PZT8, PZT-5H provided by Sunny Tech were used. Various solid loading slurries were prepared with the measurements of pH, viscosity and zeta potential 1,25 wt% optimum dispersent content was determined for slip with 72 wt% solid loading. Gypsum molds and slips containing 72 wt% solid were used to produce parts in the form of hemishpere. Otherwise, the slurries were prepared at different pH's and the variation in their thicknesses were observed at the same time. After drying, parts were sintered at 1260°C for 240 min under PbO rich atmosphere. Microstructural examinations of sintered parts with Scanning Electron Microscope (SEM) indicated a dense and pore-free microstructure.
Synthesis of needle like NaNbO3 crystals by hydrothermal process and structural characterization
YAĞIZ ÖZEREN, 2013
In recent years, great efforts have been spent on to develop lead-free piezoelectric ceramics, which exhibits high piezoelectric and ferroelectric properties, due to the restrictions on the use of lead and other hazardous substances. One way to obtain ceramics with high piezoelectric properties to crystolographically orient them. In this study, sodium niobate (NN) powders were synthesized by hydrothermal process for the purpose of using them as template particles in textured lead free piezoelectric ceramics. Since the aim of this study is to obtain anisometric morphology, effects of temperature, OH molarity, Nb molarity and period on morphology has been investigated. Na8Nb6O19.13H2O and Na2Nb2O6.H2O phases with needle-like morphology and fiber-like morphology were obtained, respectively, between 120°C and 160°C, whereas NaNbO3 particles with cubic morphology was obtained between 160°C and 240°C. With increasing time and Na molarity, needle-like morphology was retained on but needles became larger. Precursor particles have been annealed at 400°C for 1 hour to obtain NaNbO3 particles. All of the phases and morphologies have been characterized by SEM and XRD.
Characterization of potassium sodium niobate thin films prepared by sol-gel method
YAŞAR SAYDAM, 2012
Lead-free materials are attractive due to environmental considerations. Among lead-free ferroelectrics, potassium sodium niobate [(K0.5Na0.5)NbO3 -(KNN)] is a favorable alternative to lead-based ferroelectrics, due to its comparable ferroelectric and piezoelectric properties and its high Curie temperature. Thin film ferroelectrics are very important for development of integrated devices. Ferroelectric materials are used in sensors, actuators, capacitors and memory devices. In this study, both pure and doped KNN (with CuO or Li) thin films on platin (Pt) coated silicon (Si) substrates were fabricated from alkoxide precursor solutions using sol-gel spin coating method. The films were finally annealed at 700 °C in air. During the annealing process, decomposition and phase formation behaviour of the green films were monitored by DSC/DTA and FTIR analysis. Their structural and electrical properties were investigated using XRD and SEM techniques and polarization-electric field (P-E), leakage current and fatigue measurements, respectively. Undoped KNN thin film with K:Na ratio of 0.5:0.5 showed a polarization-electric field (P-E) hysterisis loop with 2Pr value of ~40 µC/cm2. CuO doping, decreases the value of leakage current in thin films.
Fabrication and characterization of lead based and lead free piezoelectric ceramic fibers
AHMET SERKAN TEKDAŞ, 2011
Lead based piezoelectric ceramics have a wide field of application such as medical iamging, sonars, actuators, transducers and sensors due to their excelent piezoelectric properties. The most promising material to replace lead based piezoelectrics is potassium sodium niobate (KNN). The aim of this study is preparation of lead zirconate titanate (PZT) fibers by sol-gel method and KNN fibers by a new and novel alginate gelation method, fabrication of piezocomposites from the fibers and their electrical characterization.
Investigation of the electrical properties of copper oxide and lithium oxide doped potassium sodium niobate lead-free piezoelectric
AYŞE BERKSOY, 2011
Lead-based piezoelectric ceramics are widely used in sensors, actuators and transducers due to their excellent piezoelectric and ferroelectric properties. Moreover, owing to their high electric field induced strain, lead-based materials are also important for electromechanical actuator applications. However, lead based-ceramics have caused environmental problems and threatened human health. Thus, lead-free piezoelectric ceramics are being investigated intensely due to the increasing environmental awareness. Among various lead free piezoelectric materials, ceramics based on potassium sodium niobate (KNN) are one of the best candidates because of their high piezoelectric properties comparable to PZT, high Curie temperature (~420oC) and large electromechanical coupling coefficients. In this study, pure KNN, 0.5 % and 1.0 % CuO added KNN, 7 % Li doped KNN (KL) and (K0.465,Na0.465)NbO3+1.0 mole % CuO (KLC) were prepared through conventional sintering methods.
Development of texture in the lead-free ferroelectric ceramic fibers with tungsten bronze structure and electrical characterization of 1-3 composites
SİNAN DURSUN, 2011
Commercially available lead-containing 1-3 piezocomposites have a wide field of application from underwater sonar systems to medical imaging systems. The objective of this thesis is to fabricate alternative lead-free 1-3 piezocomposites that can replace the commercially available lead-containing ones. However, non of the lead-free alternative piezoelectric ceramics can directly match the properties of PZT. The doping of these compositions have also failed to provide a viable performance. Thus, the main solution to improve the properties and performance of the lead-free piezoelectric seems to be to produce them with a crystallographic texture though preferred grain orientation.
Fabrication processes of Pb(Zr,Ti)O3 ceramic fibers formed of solid cross section
EMRE TEKEL, 2011
Piezoelectric transducers are devices which transform one type of energy to another by taking advantage of the piezoelectric properties of certain crystals or other materials. They transform the pressure, a mechanical input into electrical signals and conversely electrical input into shape change or vibration, a mechanical or an acoustic output. Usually PZT ceramics can be produced in the shape of disc, plate and ring using a dry pressing and tape casting methods. However bulk ceramics have low hidrostatic sensitive and high acoustic resistance. This problem can be solved by creating ceramic-polimer composites or by fabricating ceramics in hollow shell form. High hydrostatic piezoelectric sensivity is possible with sandwich type piezo composites which have spaces inside but these type of composites have lower mechanical strenght than ceramic fiber polymer piezocomposites. In this study, Our Slurry is formed into fiber shape by being drawn off from fiber-extrusion device and than these fibers retain their form the ion exchange reaction between Na and Ca ions. The electrical characteristics of these composites are examined.It is observed that these composites have ferroelectric behaviour.
The investigation of grain orientation and texture formation by the effect of electric and magnetic field in piezoelectric ceramics
MUSTAFA YUNUS KAYA, 2010
Design, dimensions and compositions are the parameters that affect the electrical and mechanical properties of piezoelectric ceramic materials. Beside these parameters, microstructure causes measurable (distinguishable) changes on properties of piezoelectric ceramics as well. So, improving microstructure to obtain higher properties in specific directions; grain orientation and texture formation is realized by various ceramic processing techniques. In this thesis study, it's aimed to obtain grain orientation and texture formation under electrical and magnetic field during the gel casting process in piezoelectric ceramics.
Characterization of piezoelectric transducer fabricated by the slip casting method
HAKAN YANIK, 2003
Dimension, shape and materials choice are the most basic characteristics of a piezoelectric ceramic transducer determining the device performance. PZT ceramics are usually fabricated in simple shapes, such as plates, disks and rings, using conventional die pressing and tape casting techniques. However, bulk PZT has a low hydrostatic sensitivity and high acoustic impedance. These can be alleviated by using piezoelectric ceramic-polymer composites, or introducing air backing into the transducer structure by using ceramic shapes with hollow spaces. Properties and performance of piezoelectric transducers are also affected from the shape of the transducer. In this regard, using ceramic shells with thin walls or ceramic with varying wall thicness or complex shapes may enhance the device performance. In this study, piezoelectric ceramics were fabricated in the form of thin shell hollow bodies and in various shapes by slip casting technique and fabricated parts were characterized for transducer applications.
Ceramic forming by using alginate gellation process
BENGÜ YAPAR, 2003
Alginate is an unbranched linear polymer which is extracted from kelp, when ammonium and sodium salts of alginic acid is prepared in a liquid solution, it undergoes gellation in the presence of multivalent cations such as Ca (except Mg2+). The aim of this work is to produce piezoelectric ceramic fibers through extrusion of ceramic slurries and in-situ gelation utilizing the alginate content. The influence of slurry content and additives on the electrical characteristics was investigated.
Production of PZT based Pb(Zr, Ti)O3 by gel casting process
DİLEK ABANOZ, 2002
Dimensions, shape, and materials choice are the most basic characteristics of a piezoelectric ceramic transducer determining the device performance. Gel casting method has mostly been used in shaping of various technical ceramics, however, it can also be applied to produce piezoelectric ceramic transducers with complex shapes. In this study, the processing conditions for gelcasting of piezoelectric ceramics was investigated with the aim of fabricating piezoelectric ceramic transducers with complex shapes containing hollow inner spaces. The lead titanate zirconate solid solution, commercially known as PZT-4, was used in the experiments.