Characterization of nanostructure of naturally occurring disordered sp2 carbon by impedance spectroscopy

We analyzed main structural models of sp2 carbon with a structure similar to glassy carbon from the point of view of impedance spectroscopy in the range from hertz frequencies to 15 MHz. We used samples of natural carbon (shungites, anthraxolites) with a structure and properties close to synthetic glassy carbon. The impedance spectroscopy results were compared to high-resolution transmission electron microscopy (HRTEM) images, which revealed a complex nanoscale structure including stacks of misoriented graphene layers, multilayer ribbons, and closed fullerene-like structures. The high locality of the HREM method often does not allow identifying the predominant nano-sized structure if two or more types of structural elements are observed in one sample. Using impedance spectroscopy, we found samples with an inductive type of resistance indicating predominant extended and tortuous elements (ribbons, fibrils), as well as samples with a capacitive type of resistance with a significant predominance of nano-sized stacks of graphene layers with impurities/dielectric gaps and micropores.