The B2O3-La2O3 binary system contains a narrow glass domain around the La2O3.3B2O3 metaborate composition. This glass domain is of interest in the field of nuclear waste containment glasses, rich in rare-earths and B2O3, and as optical materials. An extensive study of the structure and crystallization properties of these glasses has been undertaken recently1-3. In this paper, we focus on the lanthanum metaborate composition, that melts congruently at 1140°C. When undercooled, the crystallization of this melt is characterized by a heavily heterogeneous nucleation and a high activation energy for the crystal growth (~ 800 kJ.mol-1). To understand these peculiar properties, we compare the crystal and the melt structures, using a range of complementary techniques. 11B and 17O MAS NMR results do not indicate significant differences regarding the fraction of fourfold coordinated boron and the fraction of non-bridging oxygens in the crystal and in the glass, while Raman (performed on a series of binary glasses around the LaB3O6 composition) reveals a complex borate network with a great variety of superstructural units, dissimilar to that of the crystal. RE sensitive spectroscopic tools such as optical spectroscopies (Nd3+ and Eu3+ substituted for La3+) and EXAFS pointed out shorter RE3+-NBO interactions in the glass. X-ray wide angle (WAXS) and neutron scattering measurements have been carried out to produce the total structure factors and allow the building of structural models for the glass, allowing a deeper insight into the differences and relationships to the crystalline structure.

1 O. Majérus, H. Trégouët, D. Caurant, and D. Pytalev, J. Non. Cryst. Solids, vol. 425, pp. 91–102, 2015.

2 D. S. Pytalev, D. Caurant, O. Majérus, H. Trégouët, T. Charpentier, and B. N. Mavrin, J. Alloys Compd., vol. 641, pp. 43–55, 2015. 3 H. Trégouët, D. Caurant, O. Majérus, T. Charpentier, L. Cormier, and D. Pytalev, Procedia Mater. Sci., vol. 7, pp. 131–137, 2014.