Cation speciation, compactness, and structure-property correlations in manganese aluminosilicate glasses

We report on the elastic properties of xMnO-Al2O3-(6-x)SiO2 manganese aluminosilicate glasses, in which pronounced exchange coupling and antiferromagnetic interaction occurs among the paramagnetic Mn2+ ions. X-ray absorption reveals a Mn-O bond length of similar to 2.1 angstrom, and a distance of similar to 3 angstrom between Mn2+ ions in sixfold coordination, further corroborated by electron paramagnetic resonance and dynamic photoluminescence spectroscopy. This indicates the presence of edge-sharing MnO6 units, in resemblance to edge-sharing MnO8 in the crystalline Spessartine garnet Mn3Al2[SiO4](3). We argue that these cluster species have a profound effect on material stiffness: the compact structure of manganese aluminosilicate glasses enables a Young's modulus in the 100 GPa range and a Poisson's ratio of about 0.3. This exceeds the compositional trend with cation field strength observed for other aluminosilicate glasses.