An Anomalous Dissipation Factor Maximum in Sapphire

Abstract

The temperature and frequency dependencies of the dielectric properties of sapphire were determined by guarded measurements within the ranges −160° to 400°C and 102 to 104 cps. A broad dissipation factor maximum, exhibiting apparently anomalous behavior, was observed. Although the frequency at which the maximum occurred was exponentially temperature-dependent, activation energy values calculated on the basis of a dipolar relaxation model varied reversibly between 0.2 and 0.5 eV as a function of vacuum heat treatment at 400°C and of exposure to dry hydrogen, dry oxygen, or moist air. The dissipation factor behavior which would result from two alternative mechanisms, interfacial polarization and resonance, is discussed briefly on the basis of the possible existence of variable conductivity surface layers and the possible presence of hydrogen in the vicinity of dislocations.