Ionic Thermocurrents in Dielectrics

The ionic thermoconductivity (ITC) method, consisting of the study of the thermally activated release of dielectric polarization, is studied in great detail in alkali halide crystals. The (divalent metal ion, cation vacancy) dipoles give rise to an ITC band below 0°C, whose area is proportional to the polarizing field. The activation energy for dipole orientation can be obtained with an accuracy of 0.1%, when there are no overlapping bands. It is shown that the sensitivity of the ITC in detecting small contributions to the polarization (down to 2×${10}^{15}$ dipoles per ${\mathrm{cm}}^3$) or in separating overlapping relaxation processes is greater than that of methods presently employed. The solubility of the impurities can be studied by measuring the ITC of samples subjected to annealing at a fixed temperature. Intense ITC bands appearing in KCl between 280 and 430°K are probably due to contact effects. Measurements on other substances such as quartz, calcite, and Teflon show that by means of a single ITC measurement one obtains a complete qualitative picture of the polarization in a dielectric.