Microwave dielectric properties of sodium ferrite

摘要

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 1,100℃. X-ray was used to characterise the structure and scanning electron microscopy to observe the morphology. For treatment temperatures below 800℃, NaFeO_2 phase was observed, showing long grains with needle habit. For higher temperatures, Na_3Fe_5O_9 crystal phase was present, with granular and bigger grains than the other crystal phase also present, Fe_2O_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_3Fe_5O_9 phase.