Electrochemical gas sensor materials studied by impedance spectroscopy - Part I: Nasicon as a solid electrolyte

Impedance spectra of the solid electrolyte (Nasicon) were investigated by means of complex impedance in the frequency range 0.1 Hz-1 MHz at temperatures between 298 and 873 K. A plausible equivalent circuit consisting of resistor and constant phase element in series was proposed. Pronounced effect of electrode structure on impedance spectra has been observed. The equivalent circuit for the sample with Pt blocking electrodes in the temperature range 298 K-773 K is composed mostly of the CPE element, representing electrode-material interface (Warburg impedance). On the other hand, the Nasicon sample with porous Pt electrodes may be simulated by the circuit formed from the resistance R and the CPE element in series. At 573 K and above the CPE element is reduced to the simple Debye capacitor. The determined electrical conductivity and activation energy of conductivity are in general agreement with those for bulk of Nasicon reported in the literature.