Low Frequency Dispersion in Ionic Crystals

Abstract

A new region of anomalous electrical response has been observed at low frequencies in ionic crystals that have been treated to introduce relatively large number of lattice defects. The crystals thus far studied include various alkali halides and silver chloride. The effect is attributed to a jumping of the positive ions to vacant lattice sites under the influence of the applied field. This jumping is observed as a relaxation process, producing a change in the dielectric constant which is small and frequently within the limits of error of measurement, and an associated peak in the dielectric loss tangent which is readily measurable. This maximum of tan δ has been studied both as a function of frequency at a fixed temperature and as a function of temperature at fixed frequency. From the magnitude of the peak and position on the frequency or temperature scales it is possible to calculate the number of lattice defects present in the sample and the activation energy for diffusion U of the positive ion in the crystal. A knowledge of U allows a separation of the activation energy for conduction, (W/2)+U, into its components, thus determining W, the activation energy for hole formation.

Investigation of the tunnel effect and dielectric parameters of α-LiIO3 crystals

“…Considering that the cell parameter of the lithium iodate crystal is а 0 = 5.48 Å [5], we obtain the dipole moment μ = е·а 0 = 8.77·10 -29 C·m, which is in agreement with [12]. Then according to Breckenridge [13], we can write …”

AC and DC superimposed AC conduction in sodium fluoride thin films

“…The present value for enthalpy obtains1 from the conductivity plot is close to that reported by Varotsos et al [9] for cation vacancy migration in NaF doped with Ca2+. Breckenridge [6] cited the value of the activation energy for vacancy pair diffusion to be 0.74 eV for quenched NaF crystals. This value is quite high for vacancy pair relaxation, and might be rather due to the cation vacancy migration.…”

“…The NaF thin film is a promising candidate for optical computing elements [l to 31 or CW laser generation devices [4, 51. The electrical conduction in a NaF crystal has been reported to be due to the presence of vacancy pairs [6], impurity complexes, and cation vacancy migration [7 to 91. However, the experimentally obtained enthalpy for the cation vacancy migration has been very much different, viz.…”

Measurements of the suitability of large rock salt formations for radio detection of high-energy neutrinos

“…Because of the simple ionic structure of the NaCl crystal, there are no first-order ionic or vibrational modes that can absorb energy in this frequency range, and any absorption or scattering that does occur is due primarily to activation of lattice defects [20]. Radio-frequency (RF) absorption in dielectrics is usually described in terms of the loss tangent.…”