from 0 1 to 0 6 of the former per 1 of the latter the reason for the limited range of molar ratio is that as is clearly seen from the reaction formula 4in in 2 o 3 u20e1 3in 2 o the optimum molar ratio is 0 25 and that the range mentioned above is feasible from the practical point of view the indium oxide i film formed as described above on the surface of the substrate is oxidized into an indium oxide iii film in the atmosphere of a gas the inventors have made an elaborate study of the conversion of the indium oxide i film to the indium oxide iii film the oxidation in the atmosphere can occur in three ways the three possible reactions and typical calculations of free energy changes at main two point temperatures of each of the reactions are shown in table 1 below table 1______________________________________for change in free energymula kcal mol no reaction formula 298 u00b0 k 1000 u00b0 k ______________________________________ 1 in sub 2 o 2co sub 2 u2192 in sub 2 o sub 3 2co 48 6 28 6 2 in sub 2 o 2h sub 2 o u2192 in sub 2 o sub 3 2h sub 2 116 9 75 9 3 in sub 2 o o sub 2 u2192 in sub 2 o sub 3 171 5 121 9______________________________________ the changes in free energy in the reactions shown in table 1 suggest that the reactions tend to proceed invariably toward the right members of.