Beta-MnO2/SiO2 core-shell nanorods: synthesis and dielectric properties

Large-scale beta-MnO2/SiO2 core-shell nanorods were synthesized by hydrolysis process. The product was characterized by XRD, EDS, SEM and TEM. The thickness of the SiO2 shell layer is about 3 nm approximately 5 nm, which can be tuned by changing the amount of tetraethyl orthosilicate (TEOS) and the reaction time. The dielectric properties of the synthesized core-shell nanorods at the temperature range from 373 K to 773 K in X-band were investigated in detail and the mechanism of the dielectric response was discussed. The dielectric loss of the SiO2-coated MnO2 nanorods at 773 K was about twice than that at 373 K. The high dielectric loss is mainly attributed to the interfacial polarization and the electromagnetic impedance match between the SiO2 shell layer and MnO2 core layer. The quantitative formula between the permittivity of beta-MnO2/SiO2 core-shell nanorods and the thickness of the SiO2 shell is established, which can be used to tune the dielectric properties of the core-shell nanorods through controlling the thickness of the SiO2 shell layer.