• Soreto, Sílvia

Abstract

Materials were developed for electric and magnetic energy storage devices. Powders of lithium, sodium and yttrium ferrites were prepared by solid state reaction and sol-gel. In order to optimize the synthesis parameters, the found materials were heat treated and, later, a structural, morphological, electrical and magnetic characterization was performed. In order to achieve flexible and light materials, to be applied in electronic energy storage devices, two types of composites were prepared. A polymer matrix (SIS or PLA) was used for each type and lithium ferrite particles were dispersed therein at different concentrations. The preparation of these composites had as objective to maintain the electrical properties of the ferrite and the mechanical properties of the polymer, providing a new class of materials with industrial applicability. After their preparation, they were characterized thermally, structurally and electrically in order to obtain the most suitable for storing energy. In the low frequency range, sodium and yttrium ferrites, obtained by sol-gel, were the most promising to store energy, i.e., with higher dielectric constant and lower dielectric losses. In the microwave region, samples of sodium ferrite, prepared either by solid-state reaction or by sol-gel, were very likely to be applied in electronic devices. Regarding the magnetic characterization, the sample containing lithium ferrite, obtained by solid state reaction, was the one that presented greater magnetic susceptibility and less coercivity, being interesting in the magnetic point of view. For the composites with SIS as a matrix, the surface of the lithium ferrite particles was modified, obtaining an increasing of the dielectric constant of 15%. In the PLA-based composite, the results are promising, being an assertive choice because it is a biodegradable polymer having a lower impact on the environment.

Topics

• impedance spectroscopy
• surface
• polymer
• dielectric constant
• laser emission spectroscopy
• Sodium
• composite
• Lithium
• Yttrium
• susceptibility
• coercivity