STRUCTURAL AND OPTICAL-PROPERTIES OF SOL-GEL DEPOSITED PROTON CONDUCTING TA2O5 FILMS

Proton conducting tantalum oxide films were deposited on ITO (Indium T in Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prep ared using Ta(OC2H5)(5) as a precursor. X-ray diffraction studies dete rmined that the sol-gel films, heat treated at temperatures below 400 degrees C, were amorphous. Films heat treated at higher temperatures w ere crystalline with the hexagonal delta-Ta2O5 structure. The solar tr ansmission values (T-s) of tantala films on glass generally range from 0.8-0.9, depending on thickness. The refractive index and the extinct ion coefficient were evaluated from transmittance characteristics in t he UV-VIS-NIR regions. The refractive index values calculated at lambd a = 550 nm increased from n = 1.78 to 1.97 with increasing heat treatm ent from 150 to 450 degrees C. The films heat treated at different tem peratures showed low absorption, with extinction coefficients of small er than k = 1 x 10(-3) in the visible range. Impedance spectroscopic i nvestigations performed on Ta2O5 films revealed that these films have a protonic conductivity of 3.2 x 10(-4) S/m. The films are suitable fo r proton conducting layers in electrochromic (EC) devices.