Structural study of liquid lithium niobate by neutron diffraction role of the Li atom in the clustering near solidification

The structure of liquid LiNbO3 has been investigated by neutron diffraction using samples with different isotopic composition of lithium. The intensit y scattered by these samples has been measured for momentum transfers 0.4 A ngstrom (-1) < Q < 17.1 Angstrom (-1) and temperatures 1600 K> T> 1500 K, w hich include the undercooling domain. From an analysis of the correlation f unctions G(ij)(r) of the atomic pairs Li-Li, Li-Nb, Li-O and their structur al evolutions, given by Delta G(i-j) (r) = G(i-j) (r)1500-G(i-j) (r)(1550) made with reference to the crystalline LiNbO3 ferroelectric structure, was possible to confirm a local ordering similar to that of the crystal. The pr esence of clusters (groupings of NbO3 octahedra) is confirmed. Both regular and irregular NbO6 octahedra are observed in the liquid near solidificatio n. With its high mobility in the melt, the Li atom plays an important role in the clustering: the Li-O and Li-Nb bonds make possible the staking of fo ur octahedra groups into clusters of eight octahedra or more. The Li-Li bon ds join these groups. The diameter of the clusters is a least 22 Angstrom i n the undercooling regime.