Fabrication and characterization of aqueous sol-gel-derived LaFeO3 thin films

A novel all-inorganic aqueous sol-gel process has been developed to fabrica te LaFeO3 thin films by dip-coating. Stable, positively charged colloidal s ol pal-tides of hydrous lanthanum ferrite with an average particle size (Z( av)) of 7 nm were prepared and coated onto quartz plates under controlled c onditions. The sols have been characterized using photon correlation spectr oscopy (PCS) for Z(av) and size distribution. The redispersible gel was cha racterized by thermogravimetric and differential thermal analysis (TG-DTA) and also by isothermal heating followed by X-ray diffraction to identify th e reaction sequence to form LaFeO3. The sol-gel films as deposited were X-r ay amorphous on heating up to 500 degreesC, partially crystalline at 600 de greesC, fully crystalline and single phase at 650 degreesC and above. These films were continuous, polycrystalline, single phase, had uniform thicknes s in the range between 180 to 1000 nm, depending on deposition conditions, and showed about 80% optical transmittance The optical band gap varied from 2.7 to 3.3 eV as a function of the annealing temperature. The refractive i ndex increased with increase in annealing temperature from 1.55 at 500 degr eesC to 1.86 at 800 degreesC.