Lithium borate crystals and glasses: How similar are they? A non-resonant inelastic X-ray scattering study around the B and O K-edges

Abstract

The local environment of lithium borate glasses and their crystalline counterparts is investigated using non-resonant inelastic X-ray scattering (NRIXS) at energy losses corresponding to the B and O K-edges. Thanks to an extended series of lithium borate glasses and crystals, we have been able to finely interpret the local environments around boron and oxygen atoms in terms of coordination number, degree of polymerization of the borate network, superstructural units, and formation of non-bridging oxygens (NBOs). Even if a good local structural agreement between the glass and the crystal is found, an important structural discrepancy is found around the metaborate composition (50mol% of Li2O) rendering useless the use of the crystalline phase to describe the glassy state. In low alkali glasses, two subnetworks corresponding to a ‘Li-rich’ domain and a pure B2O3 domain containing boroxol rings have been evidenced. A spectral signature of the NBOs has also been evidenced in the π* peak of the B K-edge, making NRIXS a useful method offering a series of spectral signatures which can be used as structural probes for up-coming high-temperature or high-pressure in-situ experiments.