Tin lattice sites in inactive ITO are similar to those in In4Sn3O12
As the tin content increases above 10% the tin
lattice sites relax to a Sn-O bond length of 2.06 Å.
This is similar to the M1 site of In4Sn3O12.
As these sites fill tin begins to occupy the seven
coordinate M2 sites. Sn cannot donate an electron
in these sites. The loss of conductivity in highly
doped ITO is due to formation of an In4Sn3O12
network within the thin film.