The measuring cell is situated inside a boron nitride sleeve, graphite heater and a pressure transmitting medium made of CaF 2 . Boron nitride sleeve insulates the measuring cell from a graphite contamination. The starting sample is a fine powder, pressed between 2 coaxial cylindrical electrodes made from molybdenum foil in order to prevent iron losses from a sample. Before each measurement, the RC-parameters of the cell were calibrated for open and closed circuite. G f was calibrated by measuring the resistance of NaCl-water solutions placed between coaxial electrodes at room temperature and pressure.
Impedance is a concept more general than resistance because it take the phase shift into account.
As an exemple are plotted some measurement results at different temperatures for a gabbro sample at 10 kbar. At each temperature, data curves show two parts of circles. The left part related to high frequency mesurements describes the sample bulk electrical properties. The second part is related to grain boundary or electrode electrical properties or so-called low frequency dispersion. In order to investigate electrical conductivity of regions where partial melting occurs, we examined 2 samples.