  Nucleation is generally viewed as a structural fluctuation that passes a
critical size to eventually become a stable emerging new phase. However, this
concept leaves out many details, such as changes in cluster composition and
competing pathways to the new phase. In this work, both experimental and
computer modeling studies are used to understand the cluster composition and
pathways. Monte Carlo and molecular dynamics approaches are used to analyze the
thermodynamic and kinetic contributions to the nucleation landscape in barium
silicate glasses. Experimental techniques examine the resulting polycrystals
that form. Both the modeling and experimental data indicate that a silica rich
core plays a dominant role in the nucleation process.
