It was noted that, under chemical reduction at 620K in an atmosphere of methanol in a N carrier gas, this material gave up lattice O to form highly mobile vacancies. These vacancies acted as donors and were situated at about 0.4eV below the conduction band edge. The band-gap was equal to 2.7eV. Because of the possibility of removing up to 1% of the lattice O and yet maintain crystallographic stability, it was relatively easy to produce donor carrier densities of up to 1020/cm3.

W.M.Sears, S.M.McIntyre: Journal of Applied Physics, 1996, 79[10], 7703-7