Structural studies and melting of bismuth nanocrystals in reduced bismuth germanate and bismuth silicate glasses

Bismuth nanoclusters embedded in germanate glass matrices and surface layer of bismuth grains have been obtained by thermal treatment in hydrogen atmosphere of Bi0.33Ge0.67O1.84 and Bi0.57Si0.43O1.72 glass. The composite Bi-glasses were investigated by differential scanning calorimetry, X-ray diffraction and atomic force microscopy methods. A depression of the melting point of Bi from 544 to 387 K was found for nanosized bismuth particles embedded in glass and to 502 K when these are on the surface. It is shown that melting and solidification of bismuth nanocrystals induce a large change in surface conductivity of reduced glasses. A simple two-layer model of reduced glasses explains the evolution of surface layer and electrical properties of the materials during the reduction process.