Effect of Crystal Orientation on Conductivity and Electron Mobility in Single‐Crystal Alumina

Abstract
The electrical conductivity of high‐purity, single‐crystal alumina is determined parallel to and perpendicular to the c‐axis. The mean conductivity of four samples of each orientation is a factor 3.3 higher parallel to the c‐axis than perpendicular to it. The conductivity as a function of temperature is attributed to extrinsic electron conduction at temperatures from 400° to 900°C and intrinsic semiconduction at temperatures from 900° to 1300°C. In the high‐temperature regime, the slope on all eight specimens is 4.7 ± 0.1 eV. Hence, the thermal bandgap at 0 K is 9.4 ± 0.2 eV.