THE SHAPE OF COMPLEX IMPEDANCE ARCS FOR ALKALI ION CONDUCTING GLASSES

A method of using complex impedance plots to determine dc resistances is investigated in which the shape of the arc is assumed to be the same at all temperatures. Using a reduced impedance plot on which measurements made at several different temperatures are all plotted together, least squares calculations are used to determine the best-fitting depressed circular arc (DCA) and elliptic arc (EA). The technique is applied to a number of single alkali glasses in the system Li2O-B2O3-SiO2. It is shown that there are systematic departures from both DCA and EA but that the EA is the most accurate at very low frequency end. The EA gives extrapolated dc resistivities about 1 1/2% lower than does the DCA. However the scatter of dc resistivities from straight line Arrhenius plots was higher than this. The impedance plot for a mixed alkali glass is not well fitted by either a DCA or an EA and its anomalous shape is noted.