IMPEDANCE AND DIELECTRIC-SPECTROSCOPY REVISITED - DISTINGUISHING LOCALIZED RELAXATION FROM LONG-RANGE CONDUCTIVITY

The advantages of plotting a.c. data in terms of impedance, electric m odulus and dissipation factor simultaneously are illustrated. Complex impedance is generally employed for ionic conductors because it can ea sily distinguish between bulk and grain boundary effects. However, com parison with the modulus and dissipation factor data allows easier int erpretation of the microscopic processes responsible for the measured a.c. response. In particular, the difference between localized (i.e. d ielectric relaxation) and non-localized conduction (i.e. long range co nductivity) processes within the bulk of the material may be discerned by the presence or the absence of a peak in the imaginary modulus ver sus frequency plot. Similarly, the absence or presence of a peak in th e imaginary impedance versus frequency plot can be correlated to space charge effects and non-localized conductivity. Long-range conductivit y results in nearly complete impedance semicircles but no frequency di spersion in the permittivity while localized conductivity is reflected in a frequency dependent permittivity but no measurable conductance. The degree to which these assignments may be made is related to the di electric relaxation ratio (r = epsilon(s)/epsilon infinity) and the di fferences between the time constants of the different relaxation proce sses present in the material being examined.