Coloration–Decoloration Properties and Mechanisms of Nickel Oxide Films

Abstract It has been reported that nickel oxide is colored by ozone irradiation. Herein, the colored and bleached states of nickel oxide films were investigated using ozone and heat treatments. This phenomenon is known as reversible chromism. X-ray photoelectron spectroscopy analysis revealed that the NiOOH or Ni2O3 state was predominant in the colored sample; this state decreased (the color became lighter) as the heating temperature increased. Furthermore, ozone irradiation caused a compressive strain of more than 0.01%. Two types of reactions, fast and slow, were observed during the bleaching process, both exhibiting Arrhenius behavior.