Low frequency dielectric losses in thin films of NaCl and NaBr

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Abstract
Measurements of permittivity and loss tangent in the frequency range 0.01 to 1000 c/s have been made on thin polycrystalline films of sodium chloride and sodium bromide. Two regions of dielectric dispersion have been found to exist, having loss tangent maxima typically near 1 c/s and 0.003 c/s at room temperature. The activation energies associated with these peaks are respectively 0.9±0.2, 0.95±0.1 for NaCl, and 0.7±0.1, 1.0±0.1 for NaBr. Permittivity values exceed 104 at high temperatures and low frequencies. It is proposed that the results may be interpreted in terms of two interfacial polarization mechanisms, which involve the blocking of cation vacancies, firstly at intercrystalline boundaries, and secondly at the electrodes, the latter process predominating at sufficiently low frequencies.

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