Lithium oxide loss of lithium niobate nanocrystals during high-energy ball-milling

Congruent lithium niobate (LiNbO3) prepared by sintering was ground under wet conditions in a planetary mill in order to produce nanocrystals. By using gradually lower sizes of the balls in the mill, the final particle size of the crystals could be reduced to about 12-15 nm. The particle size achieved as well as the lithium oxide (Li2O) loss of the lithium niobate particles were followed as a function of the grinding time. Lithium oxide was found to be released throughout the entire milling procedure, even in the case when the particle size no longer changed upon the grinding with a particular ball size. About 12% and 20% Li2O loss was detected upon grinding with 3 mm and 0.5 mm balls, respectively. X-ray diffractometry revealed the formation of a lithium-deficient phase, LiNb3O8, the presence of which was confirmed by means of Raman spectroscopy. The LiNb3O8:LiNbO3 volume ratio achieved for 70 nm particle size as calculated from both the diffractograms and the lithium oxide loss determined by coulometric titration was assessed to be 0.39 (+/- 0.03). Correlation was revealed between the composition change of the nanopowder and the total surface area of the particle assembly calculated from dynamic light scattering measurements.