“…We consider that T m below 800 °C is too small for the intrinsic carrier conduction of Al 2 O 3 , corresponding to the other reports. 16,38) In extrinsic carrier conduction, under the naturality condition in completely ionized donors, n is expressed as exp , 46) where N d is the donor concentration, N a is the acceptor concentration, 48) To determine μ, n, and carrier type, we attempted to conduct Hall-effect measurements with a direct current magnetic field of 0.6 T using the 10 × 10 and 100 × 100 μm 2 Van der Pauw patterns. Unfortunately, the reliable data were not obtained, probably due to the high resistivity of the Al 2 O 3 samples.…”