The role of thermal analysis in optimization of the electrochromic effect of nickel oxide thin films, prepared by the sol-gel method: Part II

Thin films and the corresponding xerogels were prepared from nickel acetate precursor using the sol-gel dip-coating technique. The differences in thermal stability of the two forms of samples were studied by dynamic and isothermal thermogravimetry. For thin films, the onset decomposition temperature of acetate groups was 230degreesC and for the xerogel 250degreesC. During thermal decomposition, the formation of nanosized nickel oxide took place. Carbonate ions, which were formed during thermal decompostion of acetate groups, remained either free or bidentately coordinated to nickel. In situ monochromatic optical transmittance changes showed that an optical stability up to the 100th cycle was already achieved for films heated for 15 min at the isothermal temperature (thermal decompositon 25%). Comparison of the results obtained for nickel sulfate (Part I) and nickel acetate precursors shows that at least two parameters, the precursor used and the degree of thermal treatment, have considerable influence on the thermal stability of the thin film and also on its electrochromic response during the cycling process. (C) 2003 Elsevier B.V. All rights reserved.