Pure and Pd-doped (0.4 wt.%) SnO2 samples were prepared by the screen-printing technique starting from SnO2 powder obtained with the procedures generally used for gas sensor materials. The samples were subjected to dry and wet (50% RH) air and then resistance and capacitance were measured at different frequencies; the operating temperatures of 450 and 350 degrees C, respectively, were selected for pure and Pd-doped samples, where they present the maximum sensitivity to methane. We found a correlation between the best fitting curves of the resistance and the capacitance with the imaginary and real parts of the impedance, respectively. A tentative explanation of the observed resistance and capacitance changes by the interference of the free charge distribution with the surface states is given.
