In this study, barium strontium titanate (BST) thin films with different compositions (Ba0.9Sr0.1TiO3, Ba0.8Sr0.2TiO3, Ba0.7Sr0.3TiO3, Ba0.5Sr0.5TiO3) were produced by chemical solution deposition technique. BST solutions were prepared by dissolving barium acetate, strontium acetate and titanium isopropoxide in acetic acid and adding ethylene glycol as a chelating agent and stabilizer to this solution, at molar ratio of acetic acid/ethylene glycol, 3:1. The solution was then coated on Si and Pt//Ti/SiO2/Si substrates at 4000 rpm for 30 seconds. Crack-free films were obtained up to 600 nm thickness after 3 coating &amp / #8211 / pyrolysis cycles by using 0.4M solutions. Crystal structure of the films was determined by x-ray diffraction while morphological properties of the surface and the film-substrate interface was examined by scanning electron microscope (SEM). Dielectric constant, dielectric loss and ferroelectric parameters of the films were measured. Sintering temperature, film composition and the thickness of the films were changed in order to observe the effect of these parameters on the measured electrical properties. The dielectric constant of the films was decreased slightly in 1kHz-1 MHz range. It was seen that dielectric constant and loss of the films was comparable to chemical solution deposition derived films on literature. Maximum dielectric constant was obtained for the Ba0.7Sr0.3TiO3 composition at a sintering temperature of 800&amp / #730 / C for duration of 3 hours. Dielectric constant increased whereas dielectric loss decreased with increasing film thickness. BST films have composition dependent Curie temperature. For Ba content greater than 70 %, the material is in ferroelectric state. However, fine grain size of the films associated with chemical solution deposition and Sr doping causes the suppression of ferroelectric behaviour in BST films. Therefore, only for Ba0.9Sr0.1TiO3 composition, slim hysteresis loops with very low remanent polarization values were obtained.

ABSTRACT PREPARATION OF PLZT THIN FILMS BY CHEMICAL SOLUTION DEPOSITION AND THEIR CHARACTERIZATION Kaplan, Burkan M.S., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. Macit &Ouml / zenbaS November 2005, 125 pages In this study, La3+ was substituted into lead zirconate titanate (PZT) system by Pb1-xLax(ZryTi1-y)1-x/4O3 nominal stochiometry and it was processed via chemical solution deposition on (111)-Pt/Ti/SiO2/Si-(100) substrate.PLZT solutions were prepared by mixing two solutions, one of which was obtained by dissolving lead acetate and lanthanum acetate hydrate in 2 methoxyethanol at high temperature. This solution was then mixed with the second solution containing zirconium propoxide and titanium isopropoxide. 40ml/0.4M solution was prepared and spin coated on Pt/Ti/SiO2/Si substrates at 3000 rpm for 30 seconds. After 4 coating cycles, film thickness was reached to 600 nm. A systematic study was carried out in different regions of PLZT phase diagram tetragonal, rhombohedral and on the morphotropic phase boundry (MPB) to obtain optimized results of ferroelectric, dielectric and optical properties of the material. During the period of the work, effect of parameters on these properties such as heat treatment conditions, chemical composition of the film, microstructure and thickness of the film was investigated. The films were characterized structurally and electrically. For structural properties, X-ray diffraction technique (XRD), energy dispersive spectrometry (EDS) and Scanning Electron Microscope (SEM) were used to observe phases and surface characterization. For electrical measurements, ferroelectric tester was used to obtain dielectric constant, loss tangent and hysteresis curves. Optical transmittance of the films was also investigated by UV-VIS Spectrophotometer and optical film constants were calculated by modified envelope method. It was observed that the optimum heat treatment conditions were achieved at 7500C for 3 hours. The highest ferroelectric and dielectric properties such as remanent polarization and dielectric constant were obtained using that temperature. The dielectric constant of the films was measured in the frequency range of 1kHz-1MHz and remained almost constant in this region. The change of dielectric constant and ferroelectric hysteresis loops were obtained as a function of Zr/Ti ratio and La content. The grain size as a function of sintering temperature and La content was investigated. It was seen that as the sintering temperature was increased, the grain size of the films increased. The same tendency was also observed when the La content was increased. Fatigue behavior of PLZT thin films was also investigated by Radiant Ferroelectric Tester at 50 kHz and &plusmn / 15V. Change of remanent polarization (Pr) as a function of cumulative switching cycles (N) was drawn with the log scale of x-axis. Furthermore, leakage current characteristics of the films were also obtained by the ferroelectric tester at &amp / #61617 / 15V. It has been observed that as the La content of the film was increased, leakage current of the PLZT films decreased. Keywords: PLZT, (111)-Pt/Ti/SiO2/Si-(100) substrate, Chemical Solution Deposition.

The development of highly selective and active, long-lasting, robust, low-cost and environmentally benign catalytic materials is the greatest challenge in the area of catalysis study. In this context, core-shell structures where the active sites are embedded inside the protecting shell have attracted a lot of researchers working in the field of catalysis owing to their enhanced physical and chemical properties suppress catalyst deactivation. Also, a new active site generated at the interface between the core and shell may increases the activity and efficiency of the catalyst in catalytic reactions especially for oxide shells that exhibit redox properties such as TiO2 and CeO2. Moreover, coating oxide layer over metal nanoparticles (NPs) can be designed to provide porosity (micropore/mesopore) that gives selectivity of the various reactants by the different gas diffusion rates. In this thesis, we will discuss the concept of catalyst stabilization against metal sintering by a core-shell system. In particular we will study the mechanistic of forming core-shell particles and the key parameters that can influence the properties and morphology of the Pt metal particle core and SiO2 shell (Pt@SiO2) using the reverse micro-emulsion method. The Pt@SiO2 core-shell catalysts were investigated for low-temperature CO oxidation reaction. The study was further extended to other catalytic applications by varying the composition of the core as well as the chemical nature of the shell material. The Pt NPs were embedded within another oxide matrix such as ZrO2 and TiO2 for CO oxidation reaction. These materials were studied in details to identify the factors governing the coating of the oxide around the metal NPs. Next, a more challenging system, namely, bimetallic Ni9Pt NPs embedded in TiO2 and ZrO2 matrix were investigated for dry reforming of methane reaction at high temperatures. The challenges of designing Ni9Pt@oxide core-shell structure with TiO2 and ZrO2 and their tolerance of the structure to the conditions of dry reforming of methane will be discussed.