THEORY AND MEASUREMENT OF DIELECTRIC PROPERTIES OF ALKALI HALIDE CRYSTALS AT CRYOGENIC TEMPERATURES.
TEXAS UNIV AT AUSTIN LABS FOR ELECTRONICS AND RELATED SCIENCE RESEARCH
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The Born expression, E - alphar betarn, for the energy of interaction between two ions is used to derive a new expression for the ionic polarizability of the alkali halides. The new expression for the ionic polarizability, based upon dielectric constant measurements, gives values of the repulsive exponent n, in the Born energy relation, which agree well with values obtained from compressibility studies. The dielectric losses in a perfect crystal are examined in detail. It is assumed that there are three mechanisms which may contribute to the losses in a perfect crystal radiation damping, quantum absorption, and collision broadening. Calculations show the losses due to radiation and quantum effects to be too small to measure. A new theory of collision broadening, as applied to dielectric losses, is offered. The thermal energy of the crystal lattice produces an rms ion displacement from the equilibrium position. Experimental dielectric loss measurements in the VHF-UHF range show the actual losses to be much larger than those calculated for perfect crystals. The observed losses in NaCl and KCl are shown to be of the same nature as Debye relaxation, which are associated with crystal defects. For NaCl, a loss peak near 300 Mcsec has an activation energy of .0011 ev. and has a fractional defect density of approximately 5 x 10 to the minus 10th power.
- Electricity and Magnetism