Influence of Oxidized Magnetite Surface on Electrons Transport

Dielectric spectroscopy is a powerful tool in determining the electrical properties of the different inorganic materials. Recently, many studies were focused on the dielectric properties and charge carriers transport in ferrites. The influence of the oxides doping on the dielectric permittivity and other factors, such as dielectric losses, were studied in the details [1,2]. Generally, in the magnetite nanoparticles, three different processes can occur, depending on the temperature and frequency range. The first one, observed for ultrahigh frequencies, is related to the vibration of ions in the crystal structure and defects polarization. Two others are related to the charge carriers' generation and their movement. The transition between electrons movement in the crystal structure and in their hopping by the grain boundaries can be determined on the basis of the analysis of the imaginary part of electric modulus [3]. According to that, dielectric spectroscopy can be used to determine electrons’ behavior in function of temperature, frequency, and also the chemical composition and grain boundaries “purity”.
In the performed studies, it was stated, that the introduction of different organic molecules can change the charge carriers transport by the grain boundaries, especially by stabilization of Fe2+ or Fe3+ ions in the synthesis process. The passivation of the highly reactive surface of Fe3O4 NPs and the formation of the Fe2O3 layer can be observed by both mössbauer spectroscopy and dielectric spectroscopy, especially by analysis of the imaginary part of the electric modulus. The electron transport on grain boundaries is due to the hopping process between iron ions, therefore, the performed analysis confirmed the influence of Fe2O3 on the electrical conductivity. Moreover, the comprehensive analysis of magnetite samples with different content of the oxidized layer allowed to determine the electrical conduction model in Fe3O4@Fe2O3 core-shell nanoparticles.

References
[1] A. Radoń, Ł. Hawełek, D. Łukowiec, J. Kubacki, P. Włodarczyk, Dielectric and electromagnetic interference shielding properties of high entropy (Zn,Fe,Ni,Mg,Cd)Fe2O4 ferrite, Sci. Rep. (2019). doi:10.1038/s41598-019-56586-6.
[2] R. Ahmad, I. Hussain Gul, M. Zarrar, H. Anwar, M.B. Khan Niazi, A. Khan, Improved electrical properties of cadmium substituted cobalt ferrites nano-particles for microwave application, J. Magn. Magn. Mater. 405 (2016) 28–35. doi:10.1016/j.jmmm.2015.12.019.
[3] A. Radoń, D. Łukowiec, M. Kremzer, J. Mikuła, P. Włodarczyk, Electrical conduction mechanism and dielectric properties of spherical shaped Fe3O4 nanoparticles synthesized by co-precipitation method, Materials (Basel). (2018). doi:10.3390/ma11050735.