2003 Spring Semester
2007 Fall Semester
By Prof. M. A. Gulgun
A journey into the Nanoworld:
How thin can you separate the layers of hydroxides obtained from
controlled cement reactions? Atomically thin?
There are a number of layered structures among ceramics, like clays, calcium silicate hydrates, calcium aluminate hydrates, aluminum hydroxides, and magnesium hydroxides. They are rather soft and slippery because although the bonds in the plane of the sheets are strong the boding between the layers are rather weak like in graphite. Thus they slide easily over each other. We are actually more interested in the strong bonds in the layers. We would like to use these layers as strong reinforcement for other materials. But this requires that we can separate the layers from each other. In this process those weak bonds between the layers are best helpers. Since they are weak it is relatively easy to overcome them. Some moderate shear may do the job. In this project first we will obtain (either buy or produce) the layered structures of calcium (silicate,aluminate) hydrates which look like a flower garden made up of thin hexagonal sheets. Then we will try chemical and mechanical ways to separate them from each other such that we can use them as reinforcements.
2007 Fall Semester
By Prof. M. A. Gulgun
Crystallographic and Morphological investigation of Potassium Sodium Niobate Phases
During the synthesis of potassium sodium niobate, an important lead-free piezoelectric ceramic, many secondary phases appear in the powder batch. They all have rather distinct morphologies like cubes, pyramids, and other prismatic shapes. Their shapes closely reflect their crystallography, and we would like to characterize their crystallography and morphology. The project will entail some chemical processing, rather extensive x-ray diffraction, some electron microscopy and electron diffraction. The student should be good in wet processing in the wet labs, he or she must have some experience with x-ray diffraction and electron microscopy (at least at the SEM level).
Microwave assisted deposition of
ZnO ceramic thin films and production of ZnO nanoparticles with
Zinc oxide is an interesting wide
bandgap semiconductor (Eg= 3.37 eV) and can be doped rather
easily to become a conductor. In the insulting (no-doping) case it is a
piezoelectric ceramic. Beyond its interesting electronic properties ZnO
forms in various morphologies ranging from tripods to rings to helical
springs, to sails, to hexagonal prisms like pills, to hexagonal prisms
like pencils. The shape of the particles is strongly influences by the
pressure, temperature, and the atmosphere that ZnO particles are formed
in. Using Microwaves and a reductive-oxidative sequence we formed
various ZnO morphologies. In this project we will try to coat ZnO thin
films onto various substrate materials using ZnO, graphite, gold-island
and inert gasses. The project requires a lot of patience and good
microscopy skills. An understanding of electronic structures of ceramics
and electrical measurement techniques are advantageous.
of Epitaxial Single Crystalline Thin and Thick Yttrium Ferrite Garnet (YIG)
Ceramic Films for High Frequency Filter Applications
Tunable yttrium ferrite garnet (YIG, Y3Fe5O12) filters cover a broad band between 7 and 11 GHz, supporting a rather wide-range of microwave communications and instrumentation applications. YIG also has a high transmittance for shortwave energy. In line with the trend in miniaturization, in most of the applications, YIG is needed in the thin film form. In order to maximize the properties, single crystalline thin films are most desired. In this project, the aim is to grow epitaxial, single crystalline YIG thin films on suitable substrates. The steps include producing our won YIG powders with optimized chemistry for best properties, and with optimized physical properties. Next is choosing the substrate that will allow the best epitaxial growth. Designing and building a setup to deposit thin films on suitable substrates will be accomplished. The deposited films and produced powders will be characterized for their microwave range dielectric properties at TUBITAK MAM collaborating with Prof. Alex Vertii’s Group.
Yttrium Iron Garnet (Y3Fe5O12-YIG) is a ferrimagnetic-spin wave material which is widely used in various high speed microwave devices due to its suitable magnetic and magneto-optical properties such as high degree of faraday rotation (-3000 degrees/cm), very small linewidth in spin wave resonance, relatively low absorption and high quality factor in millimeter waveband. In our study, we will focus on producing and characterization of YIG structures for construction of a novel near field microcope. However constructing and characterization of YIG delay lines for high speed millimeter waveband tomography devices will be proposed side aim of the project.
The project will involve establishing all required technology for production and characterization of YIG structures from raw materials. Recently we were able to produce over %99,5 purity very fine YIG powders with a novel organic-complexing strategy. The proposed project will include further required steps after powder production, mainly;
Production of YIG single crystalline structures.
of bulk single crystalline with small sizes.
of YIG thin films on Gadolinium Gallium Garnet (GGG) via Liquid Phase
of launching and detection of magnetostatic waves on YIG produced
samples (The study of the dispersion characteristics) .
The construction and characterization of delay lines from YIG thin film.
Diffraction of magneto-static waves on YIG thin film surface from processed periodic structures.
Peculiar Precipitation Behavior in Yttrium Doped a-Al2O3
Yttrium was observed to enhance the creep resistance in polycrystalline alumina (a-Al2O3) by two orders of magnitude. Electron microscopy and spectroscopy studies revealed that the observed beneficial influence of yttrium is closely related to its segregation to the grain boundaries in the ceramic. Careful investigations indicated that segregation levels (GY) are increasing monotonically with grain size and /or with the total amount of the dopant in the dilute regime, following a Langmuir-MacLean type of absorption isotherm. At higher concentrations, GY shows a supersaturation behavior, which is followed by precipitation of a second phase.
Recently, we have shown that the first precipitate to form in the system is not the yttrium aluminate garnet (YAG) phase (Y3Al5O12), as predicted by the equilibrium binary phase diagram between Al2O3 and Y2O3, but is instead the yttrium aluminate perovskite (YAP) phase (YAlO3). In this project we will map out the temperature, time, and concentration ranges where these two precipitates form and transforms (if at all).