The high-temperature electrical conductivity of single-crystal alumina

The low voltage d.c. electrical conductivity of high purity annealed single-crystal alumina samples has been investigated between 800° C and 1500° C by a two-terminal method. An activation energy of 4.64 ev was obtained for the temperature range 1280° C to 1480° C. Material containing chromium as an impurity had a lower conductivity than the purer material and an activation energy of 4.26 ev. Effects likely to mask bulk-conductivity values have been examined in detail and the charge carriers identified as p-type. Crystal orientation and purity data are given. Bulk-conductivity values are ascribed to multi-valent impurity effects rather than to intrinsic behaviour as suggested by Pappis and Kingery; ionic conduction is shown to be negligible. The possibility of deriving the forbidden band-width from other data is examined.