Thermal properties and structure of zinc–manganese metaphosphate glasses

The thermal properties and some physical characteristics of the metaphosphate glassy system xMnO–(50−x)ZnO–50P2O5 were studied. Homogeneous glasses were obtained in the whole concentration range between Zn(PO3)2 and Mn(PO3)2. The metaphosphate structure of the glasses was confirmed by Raman spectroscopy. The manganese was found to have a high-spin d5-configuration in the glassy network, i.e., Mn(II), and the presence of a small amount of Mn(III) explained the purple color of the glasses, as confirmed by electron absorption spectroscopy. Thermoanalytical properties were studied by differential scanning calorimetry, thermomechanical analysis and differential thermal analysis. The phase diagram of the zinc–manganese metaphosphate system was proposed based on thermal analysis results and X-ray diffraction analysis of crystalline phases obtained after crystallization of undercooled melt. An eutectic composition was found close to 8 mol% MnO, while compositions with MnO content over 15 mol% form substitutional solid solutions. Some other properties as compositional dependence of glass transition temperature, thermal expansion coefficient and density were discussed on the basis of proposed phase diagram.