$SnO_2$ film was prepared by spraying $SnCl_4$ solution on the hot glass substrate.
The electrical conductivity of $SnO_2$ film in a thermal treatment was investigated in air at 550 ℃ - 650 ℃ and $\frac{1}{5}$ to 1 atmosphere in oxygen partial pressure at 600 ℃.
Quasichemical equations were assumed to find the mechanism of conductivity decrease in a thermal treatment.
The relation of electrical conductivity and oxygen partial pressure was σ= const $Po_2 -\frac{1}{5.8}$
It seemed that main defect of $SnO_2$ was doubly charged oxygen vacancy.
The excitation energy for formation of doubly charged oxygen vacancy was 27 ± 0.4 kcal/mole.
The kinetic activation energy of forward reaction rate constant toward an equilibrium was 14 ± 0.3 kcal/mole.
A study of film by X-ray diffraction method and electronmicroscope by replica method showed that it was polycrystalline $SnO_2$ film.
