Impedance characterization and microwave permittivity of multi-walled carbon nanotubes/BaTiO3/epoxy composites

Polymer composite materials with mixed fillers are widely investigated due to potentially superior properties they provide compared to a composite with a single filler. In this work, the electrical properties of multi-walled carbon nanotubes (MWCNT)/BaTiO3/epoxy composites are investigated using impedance measurements, modeling with equivalent circuit model, determining of alternating current conductivity in the range 10 Hz-2 MHz, permittivity measurements at frequencies 1-67 GHz, and temperature dependencies (77-290 K) of direct current conductivity. Measurements were processed to define the influence of filler combination (carbon nanotubes and BaTiO3) on dielectric properties of the epoxy composites. Nyquist diagrams indicate that all investigated composites have extensive conductive clusters. Permittivity increases monotonically with carbon nanotubes content with a steeper increase of the real part at lower frequencies. Alternating current conductivity has been determined to increase significantly at frequencies over 1 GHz. Temperature dependencies of direct current conductivity in the range 77-293 K exhibit a maximum near 180-220 K, which is shifted to the higher temperatures with the increase of carbon nanotubes content. The observed enhanced values of complex permittivity and electrical conductivity of three-phase MWCNT/BaTiO3/epoxy composites lead to a comparatively high microwave attenuation constant, which may be tuned by the carbon nanotubes content in the composite. It suggests that these composites might be perspective shielding and absorbing materials used for microwave applications.