M.Sc. (Chemistry) / Barium titanate (BaTi03) is an important material in the electronics industry as a result of its excellent dielectric properties. It has been the subject of many studies since its initial discovery, which have focussed on a wide variety of different aspects, including its synthesis, the identification of the crystal structures of its various phases, and also attempts to determine the various factors that could explain its unusual electrical properties. Since barium titanate has been studied by this wide range of disciplines, the information regarding this material is scattered over many sources. This study contains a literature survey of some of the significant work on barium titanate, in order to collect, and order, the available data into a coherent picture of the state of knowledge pertaining to the crystal structure, syntheses and electric properties of the material. From this study, it was clear that there was a distinct lack of consistent findings with respect to the identification of the tetragonal phase crystal structure. The tetragonal phase is the requisite one since it is ferroelectric, although the cubic phase also plays a significant role when the material is in the form of a very fine powder. The exact influence of the small particle size is also shown to be the object of much debate amongst the scientific community. Another area of inquiry which has attracted much attention in the past is that of the synthesis of barium titanate. The synthesis of a pure phase of barium titanate requires an intimate mixture of components which is not obtained using the standard solid-state method of synthesis, thus resulting in researchers switching to solvent-based methods of preparation. The present study also contains a summary of several of these published methods, from which four suitable methods have been selected according to certain criteria. These Criteria are that the method should be simple, use easily available materials and have been reported as having good results in terms of their dielectric properties and structural composition. It is also important that the syntheses are easy to control, to enable the extension of the work to synthesise other perovskites, poly titanates and doped barium titanate.

Ph.D. (Physics) / Please refer to full text to view abstract

Piezoelectric materials have had widespread application since their discovery both in bulk crystal and thin film applications, but thin film piezoelectrics have unlocked key applications like acoustic filtering and energy harvesting. [1] This work investigates a small subset including energy harvesting, multifunctional nanocomposites, acoustic wave resonators, and gravimetric and infrared sensing. Electroactive polymers such as PVDF-TrFE have a unique combination of characteristics including a high dielectric constant, piezoelectricity, pyroelectricity, biocompatibility, and mechanical flexibility. [2, 3, 4, 5, 6] This unique combination gives them a wide potential application space including energy harvesting, biomedical devices, drug delivery, flexible electronics, and tactile sensing. [7] In recent years, there has been significant work investigating potential composite materials based on electroactive polymers and nanoparticles. [8] This interest has been primarily driven by the increased commercial availability, tunability, and available functionalities of nanoparticles. In this work, nanocomposites of PVDF-TrFE, barium titanate (BTO), and europium barium titanate (EBTO) are investigated. EBTO is an optically active material which can add optical functionality to these active polymer composites. [9] Acoustic wave resonators including bulk acoustic wave resonators and surface acoutstic wave resonators are widely used for front end filtering technologies, but their high quality factor, small size, and low power makes them good candidates for sensing technologies. [10, 11, 12] In this work, FBARs are applied to VOC sensing and infrared sensing sucessfully.