Studies on electrochromic properties of nickel oxide thin films prepared by reactive sputtering

The non-stoichiometric nickel oxide (NiOx, x > 1) films deposited on a conducting substrate by RF magnetron sputtering have been investigated for electrochromism in alkaline solution. It was found that both Ni3+ and Ni2+ existed in NiOx films. The intercalation and deintercalation of H+ ions causes the bleaching and coloring of NiOx films. The atomic ratio of Ni and O in the NiOx films is 0.7:1 (as-deposited); 0.51:1 (bleached); 0.45:1 (colored). The maximal optical density change was found to be 0.78 at a spectral of 326 nm. With the increase of temperature of heat treatment, the electrochromic properties of NiOx films were weakened.