Microstructure of multicomponent borosilicate glasses containing MoO3

Molybdenum oxide (MoO3) is known to be only slightly soluble in borate and borosilicate glasses inducing liquid phase separation in supercooled melts during cooling. The goal of this study is to verify the tendency to immiscibility and crystallization in multicomponent compositions of the system SiO2-B2O3-Na2O-ZnO-Nd2O3-MoO3, in which the content of MoO3 varies from 15 to 80 wt%. The local structural arrangements were studied by IR spectroscopy and isolated MoO4, BO3 and SiO4 units were identified. Microheterogeneous structures with complex morphologies were identified by SEM. They have been obtained during cooling of the melts at different stages of non-equilibrium phase separation. It was established that depending on the experimental conditions the processes of crystallization and immiscibility occur simultaneously or sequentially. The reasons for immiscibility are discussed on the basis of crystallo-chemical, thermodynamic and kinetic considerations.