We wish to better understand the interaction between alkali and alkaline earth modifiers within the tellurite glass network by measuring neutron correlation functions, T(r)s, for ternary tellurite glasses. The aim is to relate the interaction of multiple modifers with the glass network to the functional properties, such as Tg, density and refractive index. To achieve this we propose to study a series of sodium-barium and sodium-calcium tellurite glasses using neutron diffraction. Direct fitting of T(r)s and isostoichiometric differences, coupled with modelling, shall be used to determine the local and medium range ordering of both tellurium and modifiers.