Dielectric loss in sodium nitrate crystals

The dielectric loss in NaNO3 crystals was studied as a function of frequency (0.1-100 KHz) at different temperatures (106-257 degrees C). The dipolar loss was analysed. The data for the temperatures below 140 degrees C were analysed using one Debye-type loss term. At higher temperatures, two Debye terms were found to be necessary. The first Debye peak has a value of tan delta of about 0.1 and its height is practically independent of temperature. It is ascribed to Maxwell-Wagner-type interfacial polarisation. The second peak (low frequency) which appears at temperatures higher than 140 degrees C increased in height with temperature. This is interpreted as due to intrinsic dipoles formed by cation vacancies and cation interstitials.