The Layered Capacitor Method for Dielectric Bridge Measurements. Data Analysis and Interpretation of Fluoride Doped ICE.

Abstract

Dielectric relaxation in ice is due to dipole reorientation and ionic diffusion. Close-coupling complicates the interpretation, especially in samples doped with proton-supplying impurities. We report on a bridge technique using ice samples sandwiched between layers of polytetrafluoroethylene (Teflon®) . An equivalent-circuit model and a nonlinear fitting algorithm have been developed for analysis of the data. A small number of discrete relaxation ranges is assumed, each characterized by a single relaxation time. Linear volume parameters can be derived from these measurements provided that the blocking layer capacitance is small compared to the series, space-charge polarization capacitance. Nonlinear conductance effects were negligible. Next, the data are used to explore the ability of the method to resolve multiple spectra. In principle, the inversion does not yield unique spectral parameters for multiple spectra. Moreover, it was found that the equivalent-circuit model has a built-in source of non-uniqueness which amplifies fitting uncertainties when ice volume parameters are ederived from ?effective? parameters of the layered capacitor. This shortcoming should be capable of improvement by further work. In conclusion, the use of linear blocking layers allowed a semiquantitative interpretation even in cases where strong overlap of relaxation processes was encountered.