OPTICAL AND ELECTROCHEMICAL CHARACTERISTICS OF NIOBIUM OXIDE-FILMS PREPARED BY SOL-GEL PROCESS AND MAGNETRON SPUTTERING - A COMPARISON

Electrochromic niobia (Nb2O5) coatings were prepared by the sol-gel-sp in-coating and d.c. magnetron sputtering techniques. Parameters were i nvestigated fbr the process fabrication of sol-gel spin coated Nb2O5 f ilms exhibiting high coloration efficiency comparable with that d.c. m agnetron sputtered niobia films. X-ray diffraction studies (XRD) showe d that the sol-gel deposited and magnetron sputtered films heat treate d at temperatures below:450 degrees C were amorphous, whereas those he at treated at higher temperatures were slightly crystalline. X-ray pho toelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb2O5. The refractive index and electrochromic colorati on were found to depend on the preparation technique. Both films showe d low absorption and high transparency in the visible range. We found that the n, k values of the sol-gel deposited films to be lower than f or the sputtered films. The n and k values were n=1.82 and k=3x10(-3), and n=2.28 and k=4x10(-3) at 530 nm for sol-gel deposited and sputter ed films, respectively. The electrochemical behavior and structural ch anges were investigated in 1 M LiClO4/propylene carbonate solution. Us ing the electrochemical measurements and X-ray photoelectron spectrosc opy, the probable electrode reaction with the lithiation and delithiat ion is Nb2O5+x Li++x e(-) <-> LixNb2O5. Cyclic voltametric (CV) measur ements showed that both Nb2O5 films exhibits electrochemical reversibi lity beyond. 1200 cycles without change in performance. ''In situ'' op tical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < lambda < 2100 nm but remain unchang ed in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measureme nts showed that spin coated films were essentially electrochromically equivalent to those prepared by d.c. magnetron sputter deposition.