Compositional study on the size distribution of nickel nanocrystals in borosilicate glasses

Abstract

For three borosilicate glasses of different B-to-Si ratio, annealed under reducing atmosphere, the effect of glass composition on the size distribution of nickel nanocrystals formed therein was studied. Depth-dependent crystal size distributions were analyzed using transmission electron microscopy, while the glass structure was examined by optical and X-ray absorption spectroscopy (XAS) and related to magnetic measurements using a superconducting quantum interference device (SQUID). A B-to-Si ratio of 0.092 resulted in a uniform crystal size distribution of small width, both with depth and with time, therefore exhibiting a large share of small nanocrystals close to the superparamagnetic limit. XAS and SQUID results indicate a more effective reduction of Ni ions in the glass of higher boron oxide content due to a higher Tg and a mean lower oxidation state induced via lowering of the glass basicity.