ETD at Indian Institute of Science
(529 recursos)
Repository of Theses and Dissertations of Indian Institute of Science, Bangalore, India. The repository has been developed to capture, disseminate and preserve research theses of Indian Institute of Science.
Mostrando recursos 1 - 14 de 14
1.
Dynamical Approach To The Protevin-Le Chatelier Effect - Rajesh, S
Materials when subjected to deformation exhibit unstable plastic flow beyond the elastic limit. In certain range of temperature and strain rates many solid state solutions, both interstitial as well as substitutional, exhibit the phenomenon of serrated yielding which also goes by the name, the Portevin - Le Chatelier (PLC) effect. The origin of this plastic instability is due to the interaction of dislocations with solute atoms. The objective of the thesis is to provide a dynamical systems approach to the study of this plastic flow instability. The thesis work discusses, within the framework of a model, the connection between microscopic...
2.
Study Of Pulsed Laser Ablated Barium Strontium Titanate Thin Flims For Dynamic Random Access Memory Applications - Saha, Sanjib
The present study describes the growth and characterization of pulsed laser ablated Bao.sSro.sTiOs (BST) thin films. Emphasis has been laid on the study of a plausible correlation between structure and property in order to optimize the processing parameters suitably for required application. An attempt has been made to understand the basic properties such as, origin of dielectric response, charge transfer under low and high-applied electric fields across the BST capacitor and finally the dielectric breakdown process.
Chapter 1 gives a brief introduction on the application of ferroelectric thin films in microelectronic industry and its growth techniques. It also addresses the present...
3.
Semiconductor Photocatalysts For The Detoxification Of Water Pollutants - Hanumanth Rao, C
Water pollution is a major concern in vast countries such as India and other developing nations. Several methods of water purification have been practiced since many decades, Semiconductor photocatalysis is a promising technique, for photodegradation of various hazardous chemicals that are encountered in waste waters. The great significance of this technique is that, it can degrade (detoxify) various complex organic chemicals, which has not been addressed by several other methods of purification. This unique advantage made this field of research to attract many investigators particularly in latter eighties and after.
This thesis incorporates the studies on the various semiconductor photocatalysts that...
4.
In-Situ Synthesis Of A12O3_ZrO2_SiCw Ceramic Matrix Composites By Carbothermal Reduction Of Natural Silicates - Mariappan, L
This thesis outlines the work done on in-situ synthesis of Al2O3-ZrO2-SiCw ceramic composites and their property evaluation. The introductory chapter deals with the literature survey on ceramic matrix composites, properties desirable for structural applications and toughening mechanisms associated with these composites. The role of whisker toughening in ceramic matrix composites, the growth mechanisms involved in whisker growth and the conditions that favour or hamper the whisker growth are also discussed. The advantages and disadvantages of in-situ synthesis of composites as compared to physical mixing are also dealt with. The objective and scope of the work undertaken are outlined at the...
5.
Thin Films And Sub-Micron Powders Of Complex Metal Oxides Prepared By Nebulized Spray Pyrolysis And Brillouin Scattering Investigations Of Phase Transitions In Solids - Murugavel, P
The thesis consists of two parts. Part 1 deals with the preparation of thin films and sub-micron powders of complex metal oxides by nebulized spray pyrolysis (NSP) and Part 2 consists of Brillouin scattering studies of solid materials exhibiting interesting phase transitions.
The simple technique of NSP has been employed to prepare thin films of A12O3, PbTiO3, Pb(Zr0.5Ti0.5)O3 (PZT) and PbZrO3 on single crystal substrate. The films were characterized by various techniques for their composition, structure, morphology and dielectric properties. Ferroelectric (FE) films of the configuration FE/LaNiO3/SiO2/Si (FE = PbTiO3 and PZT), wherein the LaNiO3 barrier electrode was also deposited on...
6.
Transport And Noise In GaAs-Based Devices - Choudhury, Palash Roy
The objective of this work was to study the noise in semiconductors and relate the transport mechanisms in the devices with the noise from the devices. The main part of the work was to set up a system for the measurement of noise in semiconductor devices. To establish the sensitivity of the system, it was calibrated at different temperatures. Some of the results from GaAs pn-junction showed some anomaly from that available in the literature. But certain points are yet to be clarified. This requires certain developments in the measurement system.
In the case of QWIPS structures, studies on some...
7.
Chemical Characterisation Of The Surfaces And Interfaces Of Barium Titanate And Related Electronic Ceramics - Kumar, Sanjiv
This thesis deals with the investigations on the atomic composition, chemical surface states and microstructural features of barium titanate and other electronic ceramics namely barium polytitantes, calcium manganites and magnesium calcium titanate by surface analytical techniques. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and interfacial characteristics, the thesis describes the synthesis of the ceramics and the methodology of the different surface analytical techniques utilized such as backscattering spectrometry (BS), an ion beam analysis (IBA) technique, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS). The XPS investigations...
8.
Charge-Transfer Associated Photoluminescence Of Rare-Earths Doped Oxide Phosphors - Nag, Abanti
Luminescent materials can be found in a broad range of everyday applications. While in the seventies and eighties, the field of luminescent materials seemed to be fairly well covered, research in nineties has been revitalized both in industry and academia. Improvements over the last three decades have led to phosphor materials that operate close to their physical limits. It cannot be expected that properties such as quantum yield and spectral energy distribution will be significantly improved or that distinctly better materials will be found in the near future. Recently, there is a considerable research activity in the field of luminescent...
9.
Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications - Jayanthi, S
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by...
10.
Multilayers And Artificial Superlattices Of Lead Magnesium Niobate-Lead Titanate Based Relaxors - Ranjith, R
The present research work mainly focuses on fabrication of compositionally modulated multilayers of (l−x) Pb(Mgi/3N2/3)O3 - x PbTiO3 (PMNPT) through multi target pulsed laser ablation technique. Heterostructures like compositionally varying multilayers; multilayers with graded interface and a ferroelectric [PbTiO3 (PT)] and relaxor (PMN) superlattices of different periodicities were fabricated. Role of artificially enhanced chemical heterogeneity and strain on enhancement of physical property was studied. Dimensional dependent ferroelectric and antiferroelectric type of polarization behavior was observed in the case of both compositionally varying multilayers and the superlattice structures fabricated. The dimensional dependence of various ferroelectric interactions like long-range, short-range and interfacial...
11.
Nonlinear Electrical And Magnetotransport Properties Of ZnO/Perovskite Manganite Ceramic Composites - Vijayanandhini, K
This thesis deals with the investigations on the nonlinear electrical and manganetotransport properties of polycrystalline multi-phase ceramic composites of Zno/pervoskite manganite. Multifunctional properties are studied such as the enhanced low-field magnetoresistance(LFMR). magnetically tuneable low-voltage nonlinear current-voltage (I-V) characteristics with larger nonlinearity coefficients suitable for semiconducting and magnetoelectric devices. A brief introduction on the structure-property correlations, electronic and magnetic structures, nonlinear electrical conduction, phase separation, grain size and grain boundary effects on transport properties of manganites are presented. The nonlinear current-voltage characteristics of ZnO based varistors are also summarized. The thesis describes the synthesis of the ceramics and the methodology of...
12.
Development Of Materials For High Emission Density Electron Emitters For Microwave Tube Applications - Ravi, Meduri
Microwave tubes are the choice of a wide range of high power and millimeter wave applications in radar, electronic warfare and communication systems. Advances in these devices are due to device innovation, improved modeling, and development of advanced materials. In a microwave tube, electron emitter is the source of electron beam and it is one of the vital components
determining the life & performance of the device. High power, high frequency
microwave tubes require electron emitters with high emission density. The
present thesis aims at developing the materials for high emission density electron
emitters. It is aimed to improve the emission density of thermionic...
13.
Investigations Of Mechanical And Thermoelectric Properties Of Group (VIB) Transition Metal Disilicides - Dasgupta, Titas
Transition Metal (TM) silicides are potential materials for different high temperature applications due to their high melting points and chemical stability at elevated temperatures. In the present work, the possible use of Gr (VIB) disilicides: MoSi2 and CrSi2 for high temperature structural application and thermopower generation respectively are investigated. Literature reports on MoSi2 indicate this material to have excellent mechanical and thermal behaviors at temperatures greater than 1273 K. The major problems limiting its use are the low temperature brittleness and oxidation at intermediate temperatures and form the scope of this work. Also, CrSi2 is reported to be a narrow...
14.
Thin Films Of A Carbonaceous Copper Oxide, Li Doped Cobalt Oxide And Li At Nanometric Dimension : Synthesis Through CVD, Solgel And Electromagnetic Irradiation And Characterisation - Das, Mahua
Thin film nanostructures may be defined as assemblies, arrays, or randomly distributed nanoparticles, nanowires, or nanotubes, which together form a layer of materials supported on a substrate surface. Because such nanostructures are supported on a substrate surface, their potential applications cover a wide area in optical, magnetic, electrochemical, electromagnetic, and optoelectronic devices.
The focus of the present thesis is the development of methodologies to grow certain thin film nanostructures of some transition metal oxides (TMOs), including copper oxides and LixCoO2, through CVD, sol-gel, and electromagnetic radiation-mediated approaches. The work towards this objective can be divided into three parts: first, the...
1.
