Chemical models of molybdenum-calcium phosphate glasses

The influence of molybdenum at varying phosphate network was studied. Three series of MoO ₃ _{}CaO-P ₂O ₅ glasses starting with calcium metaphosphate and ending with chemical compositions formally corresponding to molybdenyl metaphosphate(2+), molybdenyl pyrophosphate(2+) and their equimolar mixture were prepared. Molybdenum is incorporated as molybdenyls, which to a significantly predominant extent form the divalent colorless two-oxygen diamagnetic cation Mo ^VIO ₂ ²⁺ accompanied in low concentration by colored paramagnetic Mo ^VO ₂ ⁺ . Molybdenyls are bound in the structure by four donor-acceptor bonds with non-bridging phosphate oxygens and form a distiorted tetragonal bipyramid. A chemical model of glasses describing their actual chemical compositions and compositional dependencies was created. It has been shown that the actual chemical composition of glasses is a complicated mixture of chemical compounds. The chemical model also made it possible to have an explanation of the compositional dependences of the glass transition temperature and the coefficient of the thermal expansion of glasses.