β-MnO ₂/SiO ₂ core-shell nanorods: Synthesis and dielectric properties

Large-scale β-MnO ₂/SiO ₂ core-shell nanorods were synthesized by hydrolysis process. The product was characterized by XRD, EDS, SEM and TEM. The thickness of the SiO ₂ shell layer is about 3 nm∼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 SiO ₂-coated MnO ₂ 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 SiO ₂ shell layer and MnO ₂ core layer. The quantitative formula between the permittivity of β-MnO ₂/SiO ₂ core-shell nanorods and the thickness of the SiO ₂ shell is established, which can be used to tune the dielectric properties of the core-shell nanorods through controlling the thickness of the SiO ₂ shell layer.