Structural Elucidation of Lithium Borate Glasses Using XRD, FTIR, and EPR Spectroscopy.

A detailed investigation of the structural changes of lithium borate (LiB) glass 25LiO-(75 - )BO was conducted in the absence and presence of lead(II) oxide or aluminum oxide ( = 10 mol %) glass modifiers. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and electron paramagnetic resonance (EPR) spectroscopy were used to explore the structural properties of LiB glass by incorporating trace amounts of manganese(III) oxide (0.00-0.25 mol %) as a probe. Differential thermal analysis and XRD results for the glasses and their ceramics confirmed the integration of aluminum atoms into the glass framework by forming a lithium aluminum boron oxide Li(AlBO) crystalline phase. Lead atoms were located interstitially, which disordered the borate glass structure and produced a lithium tetraborate crystalline phase. Semiempirical modeling of the glass structures was conducted to estimate the fundamental vibrational modes of the glass materials using a parametric method 3 (PM3MM) with molecular mechanics corrections to elucidate the geometry of the borate (BO) groups and their possible vibrational modes. Our analysis revised the conventional representation of the tetrahedral BO units, which were not observed, to "distorted-trigonal" BO groups and associated with nonbridging oxygen (NBO) atoms. EPR spectroscopy established a link between the NBO in oxides and the well-defined peak at -factor ∼4.2 in glass materials, which had been assigned to iron(III) ions according to the literature.