Structure and Properties of Mixed Strontium−Manganese Metaphosphate Glasses

Structural, optical, and physical properties of glasses prepared by melt reduction in the mixed Sr−Mn metaphosphate system xMnO−(1 − x)SrO−P2O5, 0 ≤ x ≤ 1, have been investigated by vibrational, optical, EPR, and thermal techniques. Mn ions were found mostly in the +2 oxidation state and in sites of octahedral symmetry. Such sites are formed by neighboring Mn−oxygen polyhedra, where the covalent character of Mn−O bonding increases with cation mixing. The phosphate structure was found to consist predominantly of metaphosphate tetrahedral species (Q2) with a minority of pyrophosphate (Q1) and neutral (Q3) phosphate tetrahedra, whose relative abundance changes nonlinearly with MnO content. The symmetric stretching vibration of terminal PO2− units in Q2 species was employed to probe the influence of mixed Sr/Mn environments on phosphate structure, and the results suggested a deviation from the homogeneous distribution of metal cations. This was attributed to the coordination numbers of Sr and Mn ions (i.e., 8...