Nickel oxide (NiO_x) thin films doped with LaB₆ were deposited and fabricated by direct current magnetron sputtering technique onto ITO glass substrates with various ratio of argon and oxygen. LaB₆ target was just back the cathode and stacked on the nickel metal target on which six holes were drilled and punched to make the La³⁺ deposit on the substrate. The introduction and addition of La³⁺ are believed forming the defects, substituting the Ni²⁺ sites by the analysis of X-ray diffraction, scanning electron microscopy and atomic force microscopy. It obviously leads to the most roughness surface and large crystallite size of the thin films with the ratio of argon and oxygen at 45:5. Moreover, the electrochromic (EC) characteristics response for nonstoichiometric LaB₆–doped-NiO_x films show a strong dependence on crystallite size variations and surface morphology. Therefore, the as-deposited thin films above demonstrate the good optical contrast and excellent durability, especially the lifetime which can last more than 10000 s. The attempt of this work may be helpful for charactering the EC devices with doping NiO_x thin films. We think it will be a big step for the smart windows in energy efficient buildings.

Key words: LaB₆–doped-NiO_x films, optical contrast, electrochromic (EC) characteristics