Dielectric Dissipation in NaCl and KCl below 4.2°K

Abstract

Dielectric loss tangents for NaCl and KCl single crystals are presented for the frequency range 40–1000 Mc/sec from 4.2° to 1.8°K. The tan δ-frequency-reciprocal temperature surface shows considerable structure with loss tangents in the range of 2–9×10−5. Debye relaxation associated with crystal defects appears to be the dominant mechanism, with individual peaks becoming resolved above the background caused by peaks at other frequencies. A NaCl sample shows a loss peak near 300 Mc/sec at 4.2°K, with its high-frequency shoulder distorted by an adjacent peak. At lower temperatures the peaks move closer and to lower frequencies. The activation energy is estimated to be 0.0011 eV and occurs at approximately one lattice site in 5×1010. The loss mechanism suggested is electron relaxation between neighboring multivalent impurities. The loss would be indistinguishable at room temperature, but is calculated to occur at 4.6 Gc/sec with a peak loss tangent of 3.2×10−7.