CLUSTERING IN THE LINBO3 MELT

Structural analysis of the LiNbO3 melt has been carried out by means of the small angle scattering of X-rays using the synchrotron radiation and the high temperature diffraction using X-ray and neutron radiations. The usual methods were used to analyze the intensity data. A local order was defined. The radius of gyration, the interparticle distance, and form and size of the scattering particles were obtained. The clustering phenomenon is described using the diffraction results and the data of viscosity and density previously published. Formation and evolution of the particles are followed from 1673 to 1513 K including the undercooling domain. Microclusters are correctly represented by chains of two, three or four NbO6 octahedra and blocks constituted by two layers of four corner-shared niobium oxide moles tightened by a lithium atom. Macroclusters, formed by regrouping of microclusters, appear from 1550 K onwards; this fact would explain the very rapid increase of the viscosity. The physical parameters determined in this work from different methods are in good agreement with each other and also with the results obtained from the viscosity and density measurement.