Int. J. Materials Engineering Innovation, Vol. 8, No. 2, 2017 87 Copyright © 2017 Inderscience Enterprises Ltd. Microwave dielectric properties of sodium ferrite Silvia Soreto Teixeira*, Manuel Pedro Fernandes Graça and Luís Cadillon Costa I3N and Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal Email: silvia.soreto@ua.pt Email: mpfg@ua.pt Email: kady@ua.pt *Corresponding author Abstract: Ferrites cover a wide range of crystal structures and can have several applications such as high capacity batteries, electrochromic displays, waste water cleaning, low magnetisation ferrofluids, intercalation electrodes in rechargeable batteries and strong oxidising agents. Sodium ferrite exhibits interesting dielectric properties, but has not been studied in detail. In particular, at the microwave range there is very little available information about this material response. In this work, sodium ferrite, in the powder form, was obtained using the sol-gel method. The as-prepared powders, obtained by drying the gel, were pressed into cylindrical rods and heat-treated at temperatures between 400 and 1,100ºC. X-ray was used to characterise the structure and scanning electron microscopy to observe the morphology. For treatment temperatures below 800ºC, NaFeO 2 phase was observed, showing long grains with needle habit. For higher temperatures, Na 3 Fe 5 O 9 crystal phase was present, with granular and bigger grains than the other crystal phase also present, Fe 2 O 3 . The permittivity was measured at 2.7 GHz and 5 GHz and it was observed that the dielectric constant was improved with the growth of the Na 3 Fe 5 O 9 phase. Keywords: ferrites; microwaves; dielectric characterisation; resonant cavity. Reference to this paper should be made as follows: Teixeira, S.S., Graça, M.P.F. and Costa, L.C. (2017) ‘Microwave dielectric properties of sodium ferrite’, Int. J. Materials Engineering Innovation, Vol. 8, No. 2, pp.87–95. Biographical notes: Sílvia Soreto Teixeira is a PhD student in Physics Engineering at the University of Aveiro and Collaborator of the Research Laboratory I3N, recently he classified as outstanding. His topic of research interest is the physics of materials, its characterisation with the goal to be applied in electronic devices to store energy. She is a co-author in seven papers in Journals of Science Citation Index (SCI), six of them as first author and one book chapter. The research work was performed in parallel with the teaching activity in high school (since 2002) and university level (last three years). Manuel Pedro Fernandes Graça graduated in Physics Engineering. He received his Masters in Science and Materials Engineering and PhD in Physics. He worked as the Director on the Energy Department at the Prirev-Lda and since 2008, he is a researcher at the Aveiro University and member of the associated