Formation and its mechanism of copper metal layers at surface by annealing in reduced atmosphere in CuO-Li(2)O-Nb(2)O(5)-SiO(2) glass

A trace amount (0.5 mol%) of CuO-doped 40Li(2)O-32Nb(2)O(5)-28SiO(2) 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% H(2)-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 Cu(2+) ions. The mechanism of the formation of copper metals at the surface is proposed, in which the key points are the reduction of Cu(2+) 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.