If a system consists of unit with nearly freely moving charges but energy barriers between the units, so-called macro-dipoles are formed, which can result in high effective permittivity.

Dear banhegyi, 

What if I want to obtain relative low effective permittivity with carbon? is there any possibility? Like enhance the barriers between carbon particles to decrease the micro conductivity.

M. ESSONE MEZEME, S. EL BOUAZZAOUI, M. E. ACHOUR, C. BROSSEAU, Dear Hong, See my paper

"Uncovering the intrinsic permittivity of the carbonaceous phase in carbon black filled polymers from broadband dielectric relaxation", J.Appl.Phys., 109, 2011, 074107(1)-074107(11).

Dear Hong Wen, if you want low permittvity you should use low loss fillers, such as silica, or even use foams.

Dear Dr.Brosseau,

Thank you very much for your help, I will check if I can find this paper locally.

Dear Banhegyi,

Thank you for your advise, but my interest has been focus on carbonaceous materials.

Grimes, C. A., Mungle, C., Kouzoudis, D., Fang, S., & Eklund, P. C. (2000). The 500 MHz to 5.50 GHz complex permittivity spectra of single-wall carbon nanotube-loaded polymer composites. Chemical Physics Letters, 319(5-6), 460-464.