Mo5+ ions as EPR structural probes in molybdenum phosphate glasses

Glasses of P2O5-Li2MoO4-Li2O system with constant Li2MoO4 molar contents (10%), containing different amounts of the alkaline oxide (Li2O) ranging from 0 to 30 mol%, have been studied by electron paramagnetic resonance (EPR) spectroscopy. It is found that less than 1% of molybdenum ions are reduced to Mo5+, this percentage decreasing with the Li2O content. The components of g- and A-tensors are determined by computer simulations and related to structural properties using molecular orbital method. The distorted octahedral environment of Mo5+ sites is confirmed and minimal Mo-Mo distance is evaluated from the EPR linewidth as similar to 0.38 nm. At Li2O contents greater than or equal to 20 mol%, the coordination polyhedra of Mo5+ become better ordered though more distorted. The Mo-O bond covalency increases with increasing Li2O content. (C) 1998 Elsevier Science B.V.