Analysis of the ionic-thermal-current peaks with a distribution in the reorientation energy

Abstract

A computer program has been written to analyze ionic-thermal-current (ITC) peaks. The reorientation energy is assumed to have a distribution of width $\ensuremath{\sigma}$ around a mean value ${E}_{0}$. The relaxation parameters ${E}_{0}$, $\ensuremath{\sigma}$, ${\ensuremath{\tau}}_{0}$ and the number of dipoles ${N}_{D}$ are calculated by two different methods. One set is obtained after a least-squares fitting of the experimental data was performed and another set by matching a set of experimental parameters chosen with a certain criterion. The two methods are applied to analyze Sr${\mathrm{F}}_{2}$:La ITC spectra in the cases of the monoenergetic model, the Lorentzian, and the Gaussian energy distribution. The Gaussian distribution for the reorientation energy gives the most credible results, provided that the curves are efficiently cleaned. Only in this case do the two methods converge to the same set of relaxation parameters; the value of $\ensuremath{\sigma}$ is then an increasing function of the nominal concentration and not of ${N}_{D}$. The origin of the curve broadening is discussed in terms of dipole-dipole interaction, and it is shown that this effect alone is not responsible for the energy distribution. Moreover, evidence of the presence of satellite peaks on each side of the main relaxation peak is presented. These satellite peaks explain the need of analyzing only efficiently cleaned curves for obtaining reliable results.