The effects of solvents on the formation of sol–gel-derived Bi12SiO20 thin films

The sol–gel method was used to synthesize Bi12SiO20 thin films. Two synthesis routes with two different solvents, i.e., 2-ethoxyethanol and acetic acid, were used and compared. Thin films were deposited onto Pt/TiO2/SiO2/Si substrates by spin-coating at 3000 rpm and annealed at 700 °C for 1 h. A different coordination of the bismuth ion was observed in the sols prepared with acetic acid (AcOH), and as a result, stable sols were formed with a shorter gelation time tG = 84 h (c = 0.76 M), when compared with the sols prepared from 2-ethoxyethanol (EtoEtOH) tG = 580 h (c = 0.76 M). The microstructures of the Bi12SiO20 thin films prepared from sols using EtoEtOH were homogeneous and dense. On the other hand, a porous microstructure was observed for the Bi12SiO20 thin films deposited from the sol in which AcOH was used as the solvent.