Can anyone suggest a well studied powder or bulk sample that I can use as a reference sample for a impedance spectroscopy setup that I'm putting together? I would like some material, preferably a powder, that is easy to obtain, is well studied, and exhibits some futures with temperature and/or frequency. I would prefer a powder that I could compress in to a pellet. Since I'm building the setup, I want to be sure that the problems encountered are coming from the setup itself and not from the sample.

Thanks