Formation and its mechanism of copper metal layers at surface by annealing in reduced atmosphere in CuO–Li2O–Nb2O5–SiO2 glass

A trace amount (0.5 mol%) of CuO-doped 40Li2O–32Nb2O5–28SiO2 glass (mol%) exhibits the formation of copper metal layers at the glass surface by annealing at temperatures (530 °C) below the glass transition temperature (544 °C) in the reduced atmosphere of 7% H2–93%Ar. The coordination state of copper ions is examined from optical absorption and Fourier transform infrared (FT-IR) spectrum measurements, indicating the formation of Si–OH and Si–H bonds due to the diffusion of hydrogen into the inside of the glass and the reduction of Cu+ and Cu2+ ions. The mechanism of the formation of copper metals at the surface is proposed, in which the key points are the reduction of Cu2+ to Cu+ ions due to the hydrogen and the migration of Cu+ ions in the interior of the glass to the surface. The first finding on copper metal layers at the glass surface might have a potential for practical applications such as electrodes in glass.