The Evidence for Ferroelectricity on Magnetite Ceramics below the Verwey Transition

We report the temperature- and frequency-dependent dielectric spectrum of magnetite ceramic single phase samples at 77.4–300 K and 200 Hz–1 MHz. In temperature-dependent dc resistivity, the sharp transition expected in single crystals is much suppressed. At higher temperatures, the grain boundaries contribute to the relaxation process. Below 120 K, the temperature-dependent dielectric constant reveals a weak broadened peak as cooling, from our analysis this behavior may be intrinsically correlated with the charge ordering of Fe³⁺ and Fe²⁺. Under a relatively low dc bias at 77.4 K, the polarization of the magnetite ceramic decreases, while under a much stronger electrical field, the dielectric spectrum in the lower frequency region is suppressed remarkably for the excitation of carriers bounded by grain boundaries.