Mössbauer and DTA Studies of K2SO4–ZnSO4–Fe2(SO4)3 Glasses

A structural study of ternary sulfate glasses has been performed to elucidate the nature of the chemical bond and the local structure of these glasses. Mössbauer parameters (isomer shift and quadrupole splitting) show drastic decrease with an increase in the K2SO4 content. This is ascribed to the gradual change in the coordination number of iron (Fe3+) from six (Oh) to four (Td) when the K2SO4 content is higher than about 60 mol%. Lattice dynamic information obtained from low-temperature Mössbauer measurements suggests that the chemical bond between the iron and the neighboring oxygen is essentially ionic. All the Mössbauer results for the ternary sulfate glasses suggest that the Fe3+ ions are present at the vacant sites (voids) of the pseudospherical SO42− ions which are considered to be randomly packed to constitute the ionic glasses. Glass transition temperature (Tg) of these sulfate glasses, obtained from DTA measurements, also shows a gradual decrease with increasing K2SO4 content. This result is very similar to the composition dependency of the Mössbauer parameters described above, and suggests that the ionic field strength of the sulfate glasses decreases with increasing K2SO4 content. These experimental results are ascribed to the increased intermolecular bond length between the pseudospherical SO42− units.