Microstructure and frequency sensitive electrical conductivity in Fe₃BO₆:B₂O₃ of a hybrid vitroceramic nanocomposite

Abstract

Iron oxyborate Fe3BO6, a mixed compound of iron oxide Fe2O3 and iron borate FeBO3, offers multifunctional properties for electrodes, gas sensors, drugs delivery, or biological probes. To accolade useful properties, in this paper we report frequency (f) dependence of ac electrical conductivity (σac) of Fe3BO6, which is crystallized in shapes of thin plates (40–50 nm thickness) and rectangular bars (50–100 nm thickness) from an iron borate glass 40Fe2O3–60B2O3. Residual B2O3 (10–15 wt%), which remains in a vitreous phase, forms a hybrid vitroceramic nanocomposite. This B2O3 is useful to surface modify Fe3BO6 so that it turns into a strongly correlated antiferromagnet with uncompensated surface Fe3+(3d5) spins, showing only very small magnetization of the order of a few 10−4 emu/g at room temperature. The σac‐values measured at selective frequencies 0.1–103 kHz over a temperature range 300–575 K follow an activation energy varied from 0.345 to 0.244 eV, if the plot is analyzed in nearly linear parts, in raising frequency from 10 to 103 kHz. Primarily oxygen vacancies preside over a thermal assisted condition process wherein the initial σac‐value increases effectively slowly against temperature. Otherwise, Fe3BO6 with an optical bandgap 3.1 eV is a typical insulator. At f ≥ 50 kHz, a characteristically weak peak arises in a spin‐reorientation transition near 433 K. The spin‐flops, which commence on a frequency assisted σac‐value, illustrate the effect of a coupled system of the spins and charge carriers.

Crystal and local atomic structure of MgFeBO4 , Mg0.5 Co0.5 FeBO4 and CoFeBO4 : Effects of Co substitution

“…The spectroscopic, magnetic, and electronic properties of the oxyborates remain the focus of numerous studies . Special interest is connected with the oxyborates containing transition and the rare‐earth metals.…”