Disruption of stoichiometry in the growth of lithium niobate crystals

In this work, the author examines the contradictions in the experimental dependences of the density of lithium niobate crystals and the speed of propagation of surface acoustic waves on chemical composition and also the dependence of crystal composition nf the composition of the lithium niobate melt obtained by different authors. The contradiction in the first case is explained by the presence in the initial niobium pentoxide of tantalum pentoxide (0.51 mol%). In the second case, it is assumed that the surface acoustic waves propagate in a disrupted crystal layer whose density is a 0.13 g/cm3 lower than the bulk density. Finally, the principal difference between the dependences of the composition of the crystal on the composition of the melt, obtained by Carruthers and Grabmeier, is explained qualitatively by the combined presence of tantalum and by a deficit of oxygen in the initial niobium pentoxide. (author)