Growth rate effect on the dielectric properties of FeNbO4 fibres processed by the laser floating zone technique

Abstract

Fe-based materials exhibiting high dielectric constants have been attracting great attention due to their potential for application in electronic devices. In this work, iron niobate (FeNbO4) fibres were produced by the Laser Floating Zone technique, applying three different growth speeds: 5, 10 and 25 mm/h. The XRD patterns showed the presence of two phases, being the FeNbO4 the major one in all the samples. The effect of the growth speed is well perceptible in the morphology of the fibres. The dielectric measurements revealed that all samples have at least one dielectric relaxation phenomenon that is thermally activated, with the activation energy, estimated through the Arrhenius law, presenting values between 0.057 and 0.072 eV. The Nyquist plots showed the presence of a single semicircle for each temperature, that could be modelled by an equivalent electrical circuit consisting of an offset resistance in series with a parallel combination of a grain resistance and a grain constant phase element. The grain resistance increased with the increasing growth speed, from 574 to 64497 Ω, with the constant phase element showing the opposite trend, decreasing from 0.40 to 0.17 nF.