Doctorate in Applied and Engineering Physics  

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Thesis Proposal for the

Doctorate Program in Applied and Engineering Physics (DAEPHYS)

Starting in the Academic Year 2016/2017

Proposal 039

Title:Prospects on new high-K materials based on niobate systems
Objectives (recommended length: 2000-3000 char):
Enhancement and tailoring of dielectric properties of a material is a most challenging topic. Dielectrics with high permittivities(K) and low losses are required for various electronic circuits, namely high frequency devices and microwave applications (ex.wireless communications).
This project is centered in the prospection of new materials, of the niobate system, for those applications. Recent works of my group showed that this metal oxide system can lead to many different and interesting properties, making it a very versatile group of materials (but difficult to work with). More specifically, stoichiometry problems are one of the most common complications in niobium oxides and in many different niobates, where NbO6 octahedra are the basic units. Studies on niobium oxides focused in understanding and controlling the phase transformations, oxidations and oxygen vacancies are crucial to take advantage of the broad range of properties. These studies will be the starting point of this project, giving the scientific support for a deep study of the orthoniobate (ANbO4, A is a 3+ ion) system. The orthoniobates, exhibit multiple structural and dielectric phase transitions but their ferroelectric mechanism, which arises from these transitions, is still not understood. In some conditions can present colossal K values. The proponent expects that the creation of defects (acceptor or donor) will improve significantly its dielectric response and tune the ferroelectric properties by the careful control of those defects. The preparation of these materials by solid-state and sol-gel routes, techniques well established and controlled by the proponent, will permit to analyze the composition, particle size and shaping influences. The creation of defects by controlled treatments, the substitution of some trivalent ions and the preparation of those materials in different forms (ceramic, fiber, thin-film and as a polymer composite) will provide a novel base knowledge to understand the nature of their physical properties.
The major points of this proposal are:1-preparation of niobium based nano-structured materials;2-formation of defects;3-shaping in different forms;4-structural analysis;5-dielectric characterization;

Framework (recommended length: 500-2000 char):
the project will be developed within i3n framework.
Tasks (recommended length: 1000-3000 char):
The main questions of this project are: Is it possible, by controlling specific process parameters, maximize the dielectric properties of niobate based materials?; What is the nature of the dielectric response?; What is the influence of defects on these physical properties?
To answer those questions, niobium oxide base materials will be prepared by sol-gel. Factors as spatial charges, electrodes, surfaces and interfaces and grain boundaries can modify the dielectric behavior. To understand the effects of these factors, the material will be prepared in different forms. The ceramics will be prepared by sintering the powders cylinders in: i)electrical; ii)microwave ovens; iii)SPS process.
The preparation of these materials in the fiber form, will be made by Laser Floating Zone technique, which is a powerful tool for rapid growth of small diameter single crystals.
For potential applications, the niobium based powders will be also combined with a polymer, in order to gain advantages such as mechanical flexibility.
The properties of the samples produced will be studied in function of the preparation parameters. The structure will be analyzed by thermal analysis, X-ray diffraction, SEM-EDS, FTIR and Raman spectroscopy.
The electrical properties, in function of temperature, will be measured. Thermally stimulated discharge currents measurements will be made, allowing to characterize dipoles and space charge trapping and detrapping (parameters such as relaxation times and activation energies will be obtained). This measurement allows genuine peaks related to molecular vibrations and structural changes. The measurement parameters (applied field, heating rate and charging and discharging times) will be adjusted for the individual requirements of the material.
An impedance analyzer, will be used for permittivity and tunable (C-V) measurements at low frequencies (RF range). At high frequencies (MW range), resonant cavity and reflection probe setups will be used.
Research centre/lab or R&D unit hosting the thesis project:
i3n - physics Department, Aveiro University
University to which the thesis project will be presented:
UA - Universidade de Aveiro
DAEPHYS Scientific Domain in which the project fits:
Relation of the project to the Scientific Domains of DAEPHYS:
Nanotechnology, preparation of new materials, control of the preparation techniques and characterization techniques.
Candidate profile:
Preferential a student with Physics Engineering background.
Does this proposal involve more than one University?:
Synergies between the two Universities participating in the proposal:
DAEPHYS strongly encourages the presentation of thesis projects in co-supervision by researchers from two of the universities participating in the Program. In this field, explain the benefits resulting from the proposed co-supervision and the involvement of elements from the two universities, e.g. building critical mass teams, profiting from existing infrastructures or advanced equipments, profiting from expert technical know-how, etc. If the proposal involves only one University, write n/a.
(recommended length: 500-1000 char)
Does this proposal involve a company?:
Proposals involving a company:
DAEPHYS strongly encourages the presentation of thesis projects involving a company, preferably a high-tech company. These proposals have to: 1) be centered on a technological problem in which the partner company has been (or plan / would like to be) involved; 2) have a co-supervisor on the enterprise; 3) include part of the project to be carried out in the company.
(recommended length: 500-1000 char)



Name:Manuel PEdro Fernandes Gra├ža
Institution:I3N - Physics Department, Aveiro University
link to CV or indication of ORCID ID:


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